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DBMS.DOC -- Changes from V3 to V5
June 1977
Copyright (C) 1976,1977
Digital Equipment Corporation, Maynard, Mass.
This software is furnished under a license for use only on a single
computer system and may be copied only with the inclusion of the above
copyright notice. This software, or any other copies thereof, may not
be provided or otherwise made available to any other person except for
use on such system and to one who agrees to these license terms.
Title to and ownership of the software shall at all times remain in
DEC.
The information in this software is subject to change without notice
and should not be construed as a commitment by Digital Equipment
Corporation.
DEC assumes no responsibility for the use or reliability of its
software on equipment which is not supplied by DEC.
DBMS5.DOC Page 2
DBMS.DOC -- Changes from V3 to V5
June 1977
1.0 SUMMARY
DBMS-V5(240) replaces DBMS-V3 and DBMS-V4.
DBMS-V5 can co-exist with, and has been tested with, version 6.02 (and
6.03) of TOPS-10, version 1B (and 2) of TOPS-20, version 11 of
COBOL/LIBOL, and version 5 of FOROTS.
Because both V3 and V4 users will be reading this document, the
changes from V3 towards V5 have been partitioned into section 2.1 and
section 2.2 (V4 changes) and into section 2.3 (V5 changes) as much as
is feasible. V5 is a compatible upgrade of V4; however existing
DBMS-V3 applications must reload their data bases in order to use
DBMS-V5. This conversion procedure, and the other installation
instructions, are discussed in section 4.0.
The primary enhancements to DBMS-V5 are the following:
1. Support of sorted sets via indexed sequential access
2. Greatly improved performance in SCHEMA and DBCS
3. The OWNER IS SYSTEM clause
4. DBINFO as a replacement for DBSDMP and DBUTIL
5. Use of ENQ/DEQ to control access to areas
6. Much more comprehensive DMCL
7. The OCCURS phrase and additional data types
V5 ONLY:
8. Simultaneous update of data bases
9. Various journaling enhancements
These and the other enhancements are discussed in section 2. Where
relevant, incompatibilities are presented in order of decreasing
importance. However the incompatibilities presented in section 5.0
are all "benign" in the sense that they are transparent to
applications that use the supported functionality of DBMS-V5 as
defined in the documentation. They are presented only in the interest
of thoroughness.
DBMS5.DOC Page 3
2.0 EXTERNAL CHANGES
SUMMARY - FUNCTIONAL DEFINITION of DBMS-V4
The primary enhancements to DBMS-10/20 are the following:
1. Support of sorted sets via indexed sequential access
2. Greatly improved performance in SCHEMA and DBCS
3. The OWNER IS SYSTEM clause
4. DBINFO as a replacement for DBSDMP and DBUTIL
5. Use of ENQ/DEQ to control access to areas
6. Much more comprehensive DMCL
7. The OCCURS phrase and additional data types
These and the other enhancements are discussed in section 2.1.
2.1 Functional Enhancements and Differences
2.1.1 The DMCL
The general form of the DMCL is: at most one RECORDS-PER-PAGE,
JOURNAL, IMAGES, INTERCEPT, and NOTE statement, in any order...
followed by one or more ASSIGN statements.
Incidental change: RPP is now a legal abbreviation for
RECORDS-PER-PAGE.
2.1.1.1 File Specification
TOPS-10
A file spec which appears in the DMCL must comform to the following
rules. Blanks, commas, and semi-colons are ignored as elsewhere. The
allowed components may appear in any order and are a device-name, a
file-name, and a project-programmer number. The form of a device-name
is an alphanumeric followed by colon (:); the form of a file-name is
simply an alphanumeric; and the form of a PPN is [<octal number>
<octal number>]. The default device is DSK:. The default PPN is the
current path. The file-name component has no default value , being
always required.
For example, DSK:FILE[1,1].
DBMS5.DOC Page 4
TOPS-20
All components except the file-name are optional. The components
which are present must conform to the following order and formatting:
"device: <directory> filename Aaccount Pprotection". The entire spec
must not exceed 100 characters. The default device is DSK:. The
default directory is the connected directory.
For example, <allmydbs>file.
2.1.1.2 JOURNAL Statement - When present, this statement specifies
the file spec that this schema's journal file will have. If it is
absent, SCHEMA simulates a JOURNAL statement in which the device is
JRN and the file name is the schema-name. The syntax of the statement
is:
JOURNAL [IS] file-spec.
2.1.1.3 IMAGES Statement - This statement serves to delineate the
granularity of journaling that will occur in an application. The
syntax of this statement is:
IMAGES [NOT] [IN ORDER] BY COMMAND.
The default is for images to be ordered by command. When images are
ordered by command, the buffers of each open area are in effect
checkpointed after execution of each DML updating-verb. This means
that "more" writing is done to the data base and to the journal--but
conversely that the data base can be backed up in increments of single
updating-verbs...in DBMEND and at run-time.
When one requests images to not be ordered by command, checkpointing
occurs only after each user-specified transaction (ie. during a call
to JETRAN). Thus "less" writing is done to the data base and to the
journal--but conversely the data base can be backed up only in
increments of user transactions...in DBMEND and as importantly at
run-time. The mechanism of per-transaction database backup, the
JBTRAN call, is presented in subsection 2.1.6.4.
(The CODASYL DBMS specification states that, when an exception occurs
during execution of a DML updating-verb, the DBCS must return the data
base to the state it was in at the beginning of the verb. However
this is somewhat expensive as implied above. Consequently, what we
are doing is allowing the programmer to decide. By specifying that
images are not ordered by command, the programmer will be saying, "It
benefits me to decrease the cost of journaling even though that
reduces the control with which I can backup my data base and even
though that reduces exception transparency with respect to the
validity of a data base".)
There are certain applications which have to backup completely if the
application aborts for any reason. Such an application should specify
that images are not ordered by command since, even if there are no
user transactions or command-ordering, DBMEND always allows total
backup via: "START<CRLF>... END<CRLF>... MERGE BEFORE".
DBMS5.DOC Page 5
2.1.1.4 INTERCEPT/NOTE Statement - These related statements allow a
user to tell DBCS the classes of exceptions for which it should type a
message and exit, or just type a message, respectively. In other
words the facility constitutes a debugging tool, exception trace, or
means of reducing the number of ERROR-STATUS checks in an
application--depending on how it is used. The syntax of these
statements is:
INTERCEPT!NOTE (SYSTEM BIND CALL UPDATE)!ALL [EXCEPTIONS].
That is, either ALL or one or more of the others may be specified.
When a designated exception occurs, the message printed is of the
form:
[STATUS/AREA/RECORD/SET=status/area-name/others if known]
If interception was specified, an EXIT 1 is then done...which means
the user can still type CONTINUE if he wishes. The
exception-partitioning implied here is described in 2.1.5.2.
2.1.1.5 ASSIGN Statement - The syntax of the this statement is now:
ASSIGN [SYSTEM AREA] area-name TO file-spec
[RECORDS-PER-PAGE [IS] integer]
[BACKUP (BEFORE AFTER) [IMAGES]]
[BUFFER [COUNT IS] integer]
[CALC [AT MOST] integer RECORDS-PER-PAGE]
FIRST PAGE [IS] integer
LAST PAGE [IS] integer
PAGE SIZE [IS] integer WORDS
[RANGE [OF] name [IS PAGE] integer [TO PAGE] integer]
[more RANGE phrases].
Except for the RANGE clause, each clause can appear at most once.
Ordering is as presented except that the RPP, BACKUP, BUFFER and CALC
optional clauses are interchangable.
The SYSTEM AREA phrase serves to support the OWNER IS SYSTEM clause
added to the SET statement, see 2.1.2.3. Its effect is to cause the
system record (if there is need for one) to be stored in this area
(along with any other record types allowed in this area). If there is
a non-null system record and no area contains this phrase, the first
area assigned will become the system area.
DBMS5.DOC Page 6
The RECORDS-PER-PAGE clause is used to specify the maximum number of
records that can be on a page of this area. (It overrides a
RECORDS-PER-PAGE statement if one is present). If this clause is
absent, a RECORDS-PER-PAGE statement must have appeared earlier--and
the value specified there will be used. In other words, a
RECORDS-PER-PAGE statement is necessary unless each area specified has
its own RECORDS-PER-PAGE clause. Whether a global or local RPP
applies to this ASSIGN statement, it must specify at least 2 and less
than 512 records per page.
The BUFFER clause is used to specify how many page-buffers this area
will have. A buffer count of 2 is the minimum allowed. If the clause
is absent, 3 buffers will be created.
The CALC clause allows one to trade off the amount of per-area
overhead associated with calc records with the average time to
access/store a calc record. In earlier versions, there was always
precisely one calc-chain per page (one list==one word of overhead).
Thus if one expected 500 calc records in an area that had 100 pages,
the average calc-chain would unavoidably have 5 records in it. But in
V4 one could specify CALC 5 RPP and thereby reduce the average
calc-chain length to 1. Conversely if there are no calc record types
in a particular area, one can now say CALC 0 RPP.
Each RANGE clause controls where in this area a particular record type
can be STOREd. If a record type can be WITHIN this area, it may have
a RANGE clause for this area. If a record type that can be STOREd in
this area has no RANGE clause for this area, each page of the area
will constitute its range. This clause has two purposes. Its obvious
purpose is to enable the administrator to cluster records based upon
record type. Its other purpose is to make calc records insensitive to
a change in the number of pages in an area. Previously the number of
pages in an area (that contained calc records) could never be
increased since that would "throw the calc algorithm off".
2.1.2 The Schema DDL
2.1.2.1 AREA PRIVACY Clause - Because V4 supports a wider set of area
usage-modes, this clause has been expanded. There is no change in the
syntax for specifying that an area's locks are all the same, but the
separate-locks syntax is now:
PRIVACY [LOCK FOR] [EXCLUSIVE!PROTECTED] RETRIEVAL!UPDATE [IS] lock
A description of the six usage-modes is in subsection 2.1.6.1.
2.1.2.2 The Data-name Entry - This statement has been expanded and
made more host-language independent. The nature of the
incompatibility so induced is described in 2.2, notes 1 and 2. The
new syntax is:
DBMS5.DOC Page 7
02 data-name picture!size!type [OCCURS integer [TIMES]].
picture-->PICTURE [IS] same-as-v3 [usage]
size--> SIZE [IS] integer [WORDS!usage]
type--> TYPE [IS] numeric!DBKEY
usage--> USAGE [IS] DISPLAY[-6]!DISPLAY-7!DISPLAY-9
numeric->FLOAT [DECIMAL!BINARY] [REAL!COMPLEX] [integer]
-->[FIXED] [DEC!BIN] [REAL!COMPLEX] [integer [integer]]
The OCCURS clause is of course used to define an array and describe
its length. (This does not affect GET and MODIFY; each will still
process entire 02-data-names: if 02 A OCCURS 3 appeared in a schema,
GET A would get the whole array and GET A(2) would be flagged as a
syntax error).
The PICTURE clause is used to describe elementary string data; the
SIZE clause is used to describe data structures; and the TYPE clause
is used to describe numeric data (and DBKEYS). Thus the USAGE phrase
can no longer be used to described numeric data. The USAGE phrase's
sole purpose now is to state what type of string data is being
allocated: respectively SIXBIT, ASCII, or EBCDIC. Note also that the
programmer now has complete control of the unit of storage allocation
in the SIZE clause: whole words as well as any of the three string
representations. The string host-language mappings are, where !x!
=smallest integer>=x:
KEYWORDS LENGTH FORTRAN COBOL
-----------------------------------------------------
DISPLAY-6 N INTEGER(!N/5!) AS IN DDL
DISPLAY-7 N INTEGER(!N/5!) AS IN DDL
DISPLAY-9 N INTEGER(!N/4!) AS IN DDL
The NUMERIC phrase in the TYPE clause allows six types of numeric
encoding; the defaults for each pair are respectively FIXED, BINARY
and REAL. The first optional integer at the end of the NUMERIC phrase
is the data-name's precision (in binary or decimal digits according to
the 2nd keyword pair). The second integer, if applicable, is its
scale factor. A scale factor indicates that the internal form of a
fixed-point number is some number of powers-of-10 different than the
external form. The default is of course 0 (ie. no difference); -1
means external is 10 times as large; 1 means external is 1/10 as
large.
If no supported host-language intrinsically supports a particular
combination of NUMERIC keywords and the chosen precision, a syntax
error will be signalled during translation of the TYPE clause. The
default precisions for FIXED BIN, FLOAT BIN, and FIXED DEC are
respectively 35,27, and 10. The legal combinations and the
host-language mappings are as follows:
DBMS5.DOC Page 8
KEYWORDS PRECISION FORTRAN COBOL
-----------------------------------------------------------
FIXED BIN REAL < 36 INTEGER COMP S9(X2)
FIXED BIN REAL 36-71 INTEGER(2) COMP S9(X3)
FLOAT BIN REAL < 28 REAL COMP-1
FLOAT BIN REAL 28-62 REAL*8 COMP S9(18)
FLOAT BIN COMPLEX < 28 COMPLEX COMP S9(18)
FIXED DEC REAL < 19 INTEGER(X1) COMP-3 S9(prec)
Note that where only one host-language supports the keyword
combination intrinsically, the other declares it as "best it can".
For example, for FIXED DEC REAL, FORDML simply allocates 4 decimal
digits/word (ie. X1=prec/4), in terms of a "reasonable" data
type--INTEGER.
The values X2 and X3 are computed according to the following mapping.
However it is suggested that one use either FIXED BIN (35=the
default)-- or FIXED BIN 71 for double precision--unless there is a
specific need to cause numeric truncation at run-time. Consistently
using full-word precision leads to COBOL generating better object
code.
BINARY PRECISION <= P maps to DECIMAL PRECISION X2/3
----------------------------------------------------
4 1
7 2
10 3
14 4
17 5
20 6
24 7
27 8
30 9
35 10
(switch to double precision)
38 11
41 12
44 13
48 14
51 15
54 16
58 17
>58 18
2.1.2.3 The SET Entry - There are several small changes to the SET
entry.
The owner of a set can now be the system. In other words, the
programmer need no longer create a dummy record type when he wishes to
have a singular set. This affects the OWNER clause, and its new
syntax is:
OWNER [IS] record-name!SYSTEM
DBMS5.DOC Page 9
The few special rules governing singular sets are:
The system area must be placed in all sub-schemas, but it need be open
only if the system record will be referenced (see 2.1.1.5 on how to
allocate area space to the system record).
No member clause in the set entry of a singular set may have a SET
SELECTION phrase. The reason for this is intuitively reasonable:
since the DBCS knows the set is singular, it can always correctly (and
quickly) locate the "proper" set occurrence.
FIND OWNER will be allowed relative to singular sets so that a FIND
NEXT loop for a singular set can be coded as it would be for any other
set. However the meaning of a succeeding GET, MODIFY, INSERT, REMOVE,
OR DELETE is of course ill-defined and will return exception xx20.
The SET entry may optionally be separated from its MEMBER entries by a
period. Multiple MEMBER entries can also be optionally separated by
periods.
When ORDER SORTED or ORDER SORTED WITHIN is specified as a set's
ORDER, the record-name of each member record is each's major sort key.
In order to speed processing and decrease the amount of data base
space required, DBMS-10/20 uses the record's type ID rather than the
record-name itself. Type ID's are assigned in increasing sequence as
each RECORD entry is processed. This has two effects. One is that
the member record types will not be sorted in alphabetic sequence
unless they appear in alphabetic sequence; and two, that the user now
has complete control and can specifically cause non-alphabetic
sequences.
Signed RANGE KEYs will be supported in V4. Also all keys to the right
of the first RANGE will be treated as RANGE KEYs. Absence or presence
of the keyword RANGE, after its first appearance, will be transparent
to the SCHEMA processor. Finally, the existing syntactic description
is somewhat vague, the actual syntax is:
key-phrase [key-phrase ...] [duplicates-phrase]
WHERE...
key-phrase --> key-type [KEY IS] data-name-1, [dn-2,...]
key-type --> ASC!DESC!ASC RANGE!DESC RANGE
duplicates-phrase -->
DUPLICATES [ARE] [FIRST!LAST!NOT] [ALLOWED]
When sort/calc keys consist of more than one data item, it is
allowable to not ALIAS all of the items. Presumably this would be of
use when one wished to alias the minor key(s) and not the major key.
In any event, these examples portray each of the possible cases:
1. ALIAS FOR DN1 IS ALIAS1
2. ALIAS FOR DN1 IS ALIAS1 ALIAS FOR DN2 IS ALIAS2
3. ALIAS FOR DN1 IS DN1 ALIAS FOR DN2 IS ALIAS2
DBMS5.DOC Page 10
2.1.2.4 Guaranteeing Source Program Consistency - Earlier versions of
SCHEMA were somewhat lax in detecting if the subtler requirements of
the DDL were being satisfied. Version 4 attempts to guarantee that no
invalid program will translate error-free. (There is of course a
CATCH-22 incompatibility in this since some existing .DDL programs
will display errors when translated with V4). The more interesting
checks are as follows:
1. Table 4-1 on p. 4-17 in the Administrator's Manual will be
enforced.
2. When SET SELECTION is thru LOCATION MODE OF OWNER, any key so
referenced must have been declared such that DUPLICATES ARE
NOT ALLOWED for the key.
3. If an ALIAS OR USING argument is not valid, an error is
reported.
4. For each RECORD entry in which there is a LOCATION MODE IS
VIA clause, there must be a corresponding SET.
5. For each RANGE clause, the corresponding WITHIN clause must
appear.
6. If a record is declared in the same set more than once, an
error is reported.
7. If a RECORD entry contains a LOCATION MODE VIA clause and is
a member of a sorted set in which (one of) the sort key(s) is
the record's dbkey, an error is reported. This is because
such a situation is a deadlock: VIA says store the record
physically near its logical neighbors, while sorted-on-dbkeys
says logically place the record on the basis of where it is
physically.
2.1.3 The Sub-schema DDL
Conceptually there has been only one change to the sub-schema DDL;
any text (eg. 03 data-name...) that the programmer wishes to
associate with an 02-data-name will be so associated in the sub-schema
DDL. The reasons for making this change are twofold: to isolate
COBOL dependencies in sub-schemas intended for use by COBOL
applications and to allow a programmer to associate FORTRAN
information with an 02-data-name.
2.1.3.1 General Text-specifying Rules - Text is specified on a line
basis; the presence or absence of a terminating period is irrelevant.
The line(s) following a sub-schema DATA entry will be treated as text
unless its first word is COPY, 02, 01, or SET. If one wishes to have
a line of text that starts with one of these symbols, the line must be
prefixed by a plus (+). (Note that the means of explicitly entering
null text is a line consisting of +<CRLF>.)
DBMS5.DOC Page 11
Since it is likely that a data-name will have the same usage in
different sub-schemas, there must be a way to associate a data-name
with the same text in more than one sub-schema. The mechanism for
doing this explicitly is described in 2.1.3.3, but the default
mechanism is as follows. Let data-name-1 be associated with text-a in
the (i)th sub-schema in the program, and let the next sub-schema in
which data-name-1 is declared be the (j)th. Then text-a will again be
associated with data-name-1 unless text-b is actually present with
data-name-1(j)--in which case text-b will become the default for
data-name-1 in later sub-schemas.
2.1.3.2 The COPY OTHERS Statement - This statement is used to place
the "remaining" DATA entries of a RECORD entry in a sub-schema. For
example, if REC1's DATA entries were A1, A2, A3, A4 and A5, saying:
01 REC1.
would be equivalent to:
01 REC1.
02 A2.
02 A4.
COPY OTHERS.
However the usual usage of COPY OTHERS would be something analogous
to:
01 REC1.
02 A2.
THIS IS ARBITRARY TEXT
02 A4.
SO IS THIS
COPY OTHERS.
2.1.3.3 The COPY TEXT Statement - To associate data-name-1(j) with
the text associated with data-name-1 in an earlier sub-schema, one may
type the following, rather than the actual text:
COPY sub-schema-name [TEXT].
Example:
RECORD NAME IS R1
:
:
02 D1 SIZE 4 WORDS.
02 D2 TYPE FLOAT BIN.
02 D3 PIC X(5) OCCURS 4.
:
:
SUBSCHEMA NAME IS SS1.
:
:
DBMS5.DOC Page 12
01 R1.
02 D1.
03 DD1 PIC X(12).
03 DD2 PIC S9(18) USAGE COMP.
COPY OTHERS.
:
:
SUBSCHEMA NAME IS SS2.
:
:
01 R1.
:
:
SUBSCHEMA NAME IS SS3.
01 R1.
02 D1.
EQUIVALENCE (D1(1),D6BIT), (D1(3),DPINT)
02 D2.
:
:
SUBSCHEMA NAME IS SS4.
01 R1.
02 D1.
COPY SS1.
COPY OTHERS.
Sub-schemas SS1, SS2, and SS4 lead to exactly the same record
description being placed in the COBOL host program. Sub-schema SS3
places INTEGER D1(4) AND REAL D2, as well as the EQUIVALENCE
statement, in the FORTRAN host program.
2.1.4 The SCHEMA Program Interface
The V4 command line processor utilizes SCAN and WILD. The general
form of the command line is as follows:
[file-spec=] file-spec [switches]
If all or part of the output file spec is absent, the missing parts
are derived from the input file spec. The default extension for input
files is .DDL. Any extension in the output file spec is ignored. The
extension of the output file is always forced to .SCH.
In V4 there is just one class of switch, the /CREATE switch. It
controls whether the .DBS files are (re)created or left as they are:
1. If no switch is present, a .DBS file is created only if it
does not exist already.
2. If /CREATE is present, the .DBS files are always created.
3. If /NOCREATE is present, the .DBS files are never created.
DBMS5.DOC Page 13
There has been a slight change of philosophy in how areas are
addressed. Areas generally have the property that they stay put:
once they contain live data their name and directory seldom change.
Consequently when SCHEMA initializes an area, the area is associated
to its directory of creation permanently. In other words, if during
the running of SCHEMA AREA1 is ASSIGNed to FILE1, it is also ASSIGNed
to the directory which constituted the current directory path.
As noted earlier, the error detecting capability of SCHEMA has been
expanded. Additionally the error messages are now in standard form
(ie. preceded by ?DDLxxx or %DDLxxx). Lastly an error message is
accompanied by the first (and last) line of the offending source
statement, if applicable.
Important: the distinction between warnings (%) and errors (?) is
functional as well as descriptive. If the error count is greater than
0, the .SCH file (and .DBS files) will not be (re)created. If the
warning count is greater than 0 and the error count is 0, processing
will not be curtailed.
2.1.5 Exception Handling
2.1.5.1 The ERROR Special Registers - Each time a DML verb is
executed, ERROR-STATUS and ERROR-COUNT are set to well-defined values.
If no exception occurred, ERROR-STATUS equals the null-string (ie. it
is a 0-word) and ERROR-COUNT equals 0. The other three ERROR special
registers have the same value as before the verb was executed.
If an exception did occur, ERROR-STATUS equals " xxyy" and ERROR-COUNT
equals 1, where "xx" is a statement code (see 2.1.5.2) and "yy" is an
exception code (see 2.1.5.4).
ERROR-AREA will always equal the last area actually referenced.
Except for OPEN and CLOSE, ERROR-RECORD will be blanks only if the
exception occurred while DBCS was still processing the verb's argument
list. Otherwise it will be the object record's type unless the verb
"traverses" the data base. A qualified DELETE recursively traverses
the data base, FIND NEXT with a non-null record-name traverses the
data base, and FIND OWNER traverses the data base. In these cases,
ERROR-RECORD will be the record type of the last record operated upon.
ERROR-SET will be blanks unless at least one set operation has been
started at the time of the exception. Each of the following
constitutes a set operation: FIND NEXT/PRIOR/OWNER OF SET, each
auto-insert during a STORE, each actual insert during an INSERT, each
remove in a REMOVE and each auto-remove in a DELETE, and each
resorting of a set occurrence during a MODIFY.
DBMS5.DOC Page 14
2.1.5.2 Classes of Exceptions - There are several classes of
exceptions explicitly defined. ALL is of course all the valid
statement-code/exception-code combinations, SYSTEM is all the
exceptions with a code greater than or equal to 55. The SYSTEM
exceptions are discussed in some detail in the next subsection,
Failsofting. The other defined classes are partitions of the
statement-codes, which are:
STATEMENT CODE
----------------------------
HOST 00
CLOSE 01
DELETE 02
FIND 03
UNUSED 04
GET 05
UNUSED 06
INSERT 07
MODIFY 08
OPEN 09
UNUSED 10
REMOVE 11
STORE 12
RESERVED 13
RESERVED 14
BIND 15
CALL 16
The HOST statement-code is associated with the IF predicates and the
MOVE STATUS command. The BIND statement-code is associated with the
SBIND, BIND, EBIND, and SETUSE entry points. Also note that
exceptions 31 thru 36 can only be generated during binding. The CALL
statement-code is associated with all of the DBCS entry points that
are explicitly called (ie. the journaling entry points Jxxxxx and
SETDB and UNSET). The UPDATE class of exceptions refers to any
exception that happens during execution of DELETE, INSERT, MODIFY,
REMOVE or STORE.
2.1.5.3 Failsofting - V4 of DBCS attempts to guarantee two things as
regards the execution of a run-unit.
First it operates on the assumption that a critical application may
want to maintain complete control and never be returned to monitor
level against its will. DBCS serves this goal by associating an
exception code with all the exceptional conditions that it detects--it
never does an EXIT that the user did not request (the INTERCEPT
facility is a means of requesting EXITs). This rule is broken
precisely once: to place a value in ERROR-STATUS, DBCS must have been
associated with a sub-schema--consequently if the first call to DBCS
is at other than SBIND, it types the ?DBSSNI message and exits.
Secondly it attempts to guarantee that no one accesses a data base
while it or DBCS is in an undefined state.
DBMS5.DOC Page 15
One aspect of this control is the area-status-record (ASR), which is
created the first time an area is OPENed (and always has a dbkey equal
to first-page/1). When an area is OPENed for update, DBCS decrements
by 1 FH.STAT in the ASR to indicate that the area is in a state of
flux. FH.STAT is not incremented by 1 until the programmer closes the
area. If the run-unit aborts for any reason, DBMEND must be used to
revalidate the area (and reset FH.STAT to 0) before it can be OPENed
for normal usage again.
The other major aspect of control is DBCS's status word (one for each
sub-schema INVOKEd). The two user-relevant flags are the
system-in-undefined-state (SUS) flag and cannot-backup-updates (CBUU)
flag. CBUU is turned on in the following circumstances: during
exceptions 61 and 63, during OPEN if the journal device is MTA, during
the OPENing of an area for update when BEFORE IMAGES are not
requested, and in conjunction with the SUS flag if an exception occurs
during binding or while an exception is being processed (this also
causes typing of the ?DBSXWX message). The SUS flag gets turned on
for only one other reason, when an exception occurs after an updating
verb has altered one or more data base pages.
The effect of the SUS flag is as follows. If one tries to enter DBCS
while the SUS flag is set (at other than JBTRAN or a sub-schema
changing entry point), DBCS will return immediately with ERROR-STATUS
set to " xx62". However, if CBUU is not set, there is one of two ways
in which the SUS flag may get turned off.
If images are ordered by command, DBCS will automatically restore the
data base to the state it was in before the verb was entered and turn
the SUS bit off. But if for some exceptional reason the restoration
cannot be completed, the ?DBSUCR message is typed and CBUU is also
turned on.
If images are not ordered by command the program will be able to
explicitly restore the data base to its proper state even though DBCS
will have returned with the SUS bit still set. It can do this via the
JBTRAN entry point. Calling JBTRAN after an updating-exception will
restore the data base to the beginning of the in-doubt transaction,
turn the SUS bit off, and (IMPORTANT!) leave all currency indicators 0
(to eliminate the possibility of reference to now non-existent
records). If, for some exceptional reason JBTRAN fails, ERROR-STATUS
will be set to " 1663" and CBUU turned on.
In summary, there is no way for the programmer to turn off the CBUU
flag. In and of itself this is no problem since the CBUU flag is
transparent to the application unless the SUS flag is also turned on.
In this latter state however, the run-unit can essentially do nothing
with the sub-schema... and in effect DBCS no longer trusts itself.
DBMS5.DOC Page 16
2.1.5.4 The Exception Codes
EXCEPTION DESCRIPTION
---------------------------------------------------------------
00 A WARNING: the compile-time and run-time versions of
the .SCH file differ. However if a "real" exception
occurs during binding DBCS always returns the code of
that exception... but to indicate that exception 00
has occurred as well, DBCS types the %DBSCED message.
However, as a general rule, the "real" exception will
not persist after the program-unit is recompiled with
the up-to-date .SCH file.
01 Area not open
02 Dbkey inconsistent with area-name. Can also indicate
that a referenced page number is in an area that is
not in the sub-schema.
03 Record affected by concurrent application--V5 only
04 Data-name invalid or inconsistent (ie. during GET or
MODIFY with data-name list)
05 Violation of DUPLICATES NOT ALLOWED phrase
06 Current of (set/record/area) not known
07 End of set or area
08 Referenced name not in sub-schema. This can occur for
many reasons: (1) In traversing a set, if a record
type not in the sub-schema is encountered. (2) During
STORE OR DELETE, if set type owned by the object
record type is not in the sub-schema. (3) During set
occurrence selection if the VIA set is not in the
sub-schema. (4) During calc processing or in
searching a sorted set, if not all subkeys are in the
sub-schema. (5) During MODIFY, if the sort key of a
set not in the sub-schema is modified.
The solution to this problem is of course to place the
offending name in the sub-schema.
09 An update usage mode required (eg. attempt to STORE a
record while the area is OPEN for RETRIEVAL)
10 Privacy breach attempted
11 Data space exhausted (ie. no more room to STORE a
record). Note that this can occur while DBCS is
trying to store an internal record type: in
particular, the index blocks in a sorted set.
12 Unused
DBMS5.DOC Page 17
13 No current record of the run-unit
14 Object record is mandatory automatic member of the
set.
15 Attempt to REMOVE a record which is either a MANDATORY
member or not a member type at all.
16 Record is already member of set.
17 Need a record which is current of "-----", but it has
been deleted (eg. can occur during FIND CURRENT OF
"-----"; or during GET, if the record was deleted by
a concurrent run-unit).
18 Unused
19 Data conversion unsuccessful--unused for now
20 Current record of run-unit not of right record type
21 Unused
22 Record not currently member of set, analogous to xx17.
23 Illegal area-name was passed in an AREA-ID.
24 Temporary and permanent areas referenced in same DML
verb.
25 No set occurence satisfies argument values (eg. calc
value in UWA matched no owner record)
26 No record satisfied RSE, catch-all exception for FIND
verb.
27 Unused
28 Area already open
29 Unused
30 Unqualified DELETE attempted on non-empty set
NON-CODASYL EXCEPTION CODES
31 Unable to open the .sch file
32 Insufficient space allocated (eg. SIZE clause
specified less space that what the compiler actually
needed)
33 None of the areas a record type can be WITHIN are in
the sub-schema.
DBMS5.DOC Page 18
34 A set is in the sub-schema, but its owner record type
is not.
35 Dynamic use-vector full
36 Attempt to INVOKE too many sub-schemas (currently more
than 8), attempt to UNSET an empty sub-schema stack or
SETDB a full stack.
37 Argument to SETDB is not an already-INVOKEd
sub-schema.
38 Duplicate operation on resource: you have attempted
to open the journal twice; you have opened it
EXCLUSIVE and are now opening an area with USAGE-MODE
UPDATE; you are calling JSTRAN while a transaction is
already active; or you have multiple INVOKEs and have
attempted to open the same area twice.
39 DBS file not found
40 Requested access conflicts with existing access. In
other words, the resource is not available: (1) you
attempt to open an area in a USAGE-MODE incompatible
with another run-unit's control (eg. you try EXCL
RETRIEVAL and he already has it open with PROT UPDATE)
(2) you attempt to open the journal and a USAGE-MODE
conflict results. (3) you attempt to delete a record
retained by another run-unit. (4) you attempt to open
an area (or the journal) and the file-system signals a
file protection error.
41 No channel available...attempt to open too many areas
42 Area in undefined state (eg. after crash).
Internally this means that FH.STAT in the ASR is less
than 0. DBMEND should be used to FORCEOPEN the area
and return it to a valid state.
43 Area in creation state. This can happen to the system
area only. It will happen if the run-unit aborts at
just the right time during the very first OPENing of
the system area. DBCS recognizes this state by
leaving FH.STAT equal to 1 until initialization of the
system area is completed.
If this exception is returned, the programmer should
either rerun SCHEMA or, more simply, just create a
0-length file with one of the text editors.
44 Attempt to call a journal-processing entry point
before the journaling system has been initialized (by
the first OPEN that requires journaling).
DBMS5.DOC Page 19
45 Attempt to backup the data base with JBTRAN while
DBCS's CBUU bit is set (see 2.1.5.3) or when a file
(ie. journal or area) is shared for update in command
mode or for JBTRAN(gtr 0) when it is shared for update
in transaction mode.
46 Magtape service is unavailable--DAEMDB returned a
failure code.
47 Reserved
48 Reserved
49 Reserved
50 Unused
51 Unused
52 Unused
53 Unused
54 Unused
SYSTEM EXCEPTIONS
55 Pseudo-exception: DBCS types message that no
sub-schema has been initialized yet
56 Inconsistent data in .DBS file. DBMEND should be used
to restore the data base to a valid state. If the
problem can be reproduced, it probably indicates the
presence of a DBCS software error.
57 DBCS software error probably
58 Illegal argument was passed by user (or setup by host
interface).
59 No more core-memory available
60 I/O error attempting to access a .DBS file -- is DBCS
bug, is spurious, or is disk quota exceeded or file
protection failure.
61 Unable to append to journal either in normal operation
or in trying to open a journal for appending (ie.
journal in an aborted-state but not designated as done
with). This exception turns on CBUU as well as SUS
(see 2.1.5.3).
62 Attempt to enter DBCS at other than JBTRAN, SBIND,
SETDB, or UNSET while the SUS bit is on (see 2.1.5.3).
DBMS5.DOC Page 20
63 Unable to complete restoration of the proper data base
state--either in JBTRAN or when initializing a
run-unit at the start of an interleaving-unit. This
exception turns on CBUU as well as SUS (see 2.1.5.3).
64 Internal use only
65 Monitor space for ENQ entries exhausted or ENQ quota
exceeded
66 ENQ/DEQ/ENQC failure: user does not have ENQ
capabilities set or some DBCS problem
67 Unable to initialize magtape service--as opposed to it
being unavailable (eg. SYS INFO not running, DAEMDB
not running, or some DBCS problem)
68-99 Reserved
2.1.6 The Data Manipulation Language
2.1.6.1 The OPEN Statement - The only part of the OPEN statement that
has changed is the USAGE-MODE clause. The syntax is now:
USAGE-MODE [IS] [PROTECTED!EXCLUSIVE] RETRIEVAL!UPDATE
Although the syntactic change is small, three USAGE-MODEs will have
been added (the last in V5), and the meaning of each USAGE-MODE has
been brought into alignment with the CODASYL spec.
EXCLUSIVE RETRIEVAL means that no one else will be able to access the
area while you have it OPEN and that you will not be able to STORE,
DELETE, MODIFY, INSERT or REMOVE. Conversely if anyone has the area
OPEN for any reason, you will be denied access.
EXCLUSIVE UPDATE means that no one else will be able to access the
area while you have it OPEN and that you will be able to execute any
verb. Conversely if anyone has the area OPEN for any reason, you will
be denied access.
PROTECTED RETRIEVAL means that no one else will be able to update the
area while you have it OPEN and that you will not be able to call the
updating verbs listed above. Conversely if anyone has the area OPEN
for EXCLUSIVE access or PROTECTED UPDATE or UPDATE, you will be denied
access.
PROTECTED UPDATE means that no one else will be able to update the
area while you have it OPEN and that you will be able to execute any
verb. Conversely if anyone has the area OPEN for EXCLUSIVE access or
PROTECTED UPDATE or UPDATE, you will be denied access.
DBMS5.DOC Page 21
RETRIEVAL means that anyone else will be able to access/update the
area while you have it OPEN and that you will not be able to execute
the updating verbs listed above. Conversely if anyone has the area
OPEN for EXCLUSIVE access, you will be denied access.
UPDATE means that anyone else will be able to access/update the data
base while you have it OPEN and that you will be able to execute any
verb. Conversely if anyone has the area OPEN for EXCLUSIVE or
PROTECTED access, you will be denied access.
Some general comments:
All update USAGE-MODEs actually modify the .DBS file when a buffer is
written to disk. A temporary area is the only circumstance in which
there is an after-image directory, in which case a file by the name of
ASSIGNed-name.TMP is created. See section 2.4 note 7, for a
description of the organization of an area .TMP file.
The idea that different USAGE-MODEs were synonymous with different
accessing algorithms was a corruption of the USAGE-MODE concept. The
concept of USAGE-MODE has just two components: the level of shared
access to be allowed and whether modification of the area is to be
allowed.
2.1.6.2 The MOVE Statement - The syntax of this statement has not
been changed. The change is that it will now alter the special
registers AREA-NAME and RECORD-NAME to describe the currency indicator
being MOVEd. Also see subsection 2.2, note 3.
2.1.6.3 DELETing or REMOVing Current of "-----" - The meaning of FIND
NEXT of SET when current of set has been REMOVEd or DELETEd is apriori
somewhat ambiguous. Consequently, to allow this and the other
currency-based operations in this situation, some convention must be
established. The convention employed by DBMS-10/20 V4 is as follows.
The record which was NEXT of the eliminated record becomes the
canonical NEXT of SET. What this means is that, no matter what
happens to the set (short of establishing a new current of set), this
record is NEXT of SET and the record which is PRIOR to it at any point
in time is PRIOR of SET.
DELETing current of area has no effect on the operation of FIND NEXT
of AREA. This is the case because DBKEY+1 and DBKEY-1 are inherently
NEXT and PRIOR of the dbkey being deassigned--whereas the identities
of NEXT and PRIOR of a set depend on values in the record being
eliminated.
DBMS5.DOC Page 22
2.1.6.4 The JBTRAN Routine - The topic of the JBTRAN routine has been
broached in subsections 2.1.1.3 and 2.1.5.3 as well. To reiterate,
the primary reason to call JBTRAN is to turn off the SUS flag (turned
on by an updating-exception) by backing up the data base to the most
recent transaction-header. To use JBTRAN for this purpose, the
calling sequence is:
COBOL: ENTER MACRO JBTRAN USING 0.
FORTRAN: CALL JBTRAN(0)
There is potentially a second reason to call JBTRAN. If an
application, for its own reason, wants to wipe out one or more
transactions, it can do this (even though SUS is off) by giving the
number of transactions it wishes to backup as the argument to JBTRAN.
(Thus CALL JBTRAN(1) can be used in place of CALL JBTRAN(0), but the
reverse is not true because CALL JBTRAN(0) will do nothing if the SUS
bit was already off.)
It is unnecessary to do a JETRAN after cleaning up an aborted
transaction with JBTRAN because JBTRAN simulates a JETRAN of the
following form: JETRAN ("JBTRAN", number backed up).
2.1.6.5 The STATS Routine - There have been some changes to the
information that is output when STATS is called. Most of the V4
output is self-explanatory, but a couple of things do require comment.
Some of the simpler routines in DBCS have a CPU duration which is at
the border-line of resolution of the RUNTIM UUO. This means that the
statistics for these entry points may be erratic. Also the cost of
generating detailed timings is rather large. Consequently detailed
timing statistics will not be generated unless the user specifically
requests them. He does this by setting the global symbol "STATS."
non-0. The simplest way to accomplish this is:
.R LINK
*user-prog,/DEFINE:STATS.:1,etc/G
The STATS information is output on a sub-schema basis. In other
words, if one has invoked two sub-schemas, one will get two
subsections of output. Also each figure for sub-schema run-time is
the result of subtracting the value of RUNTIM at the time each
sub-schema was SBINDed from its current value.
"Same-page data base accesses" is a measure of intra-page
localization. It is incremented by 1 each time the page accessed is
the same page as was accessed the preceding time.
Lastly, reads of a temporary area's directory page are included in the
count of pages actually read from disk.
DBMS5.DOC Page 23
2.1.6.6 Passing Strings to DBCS - There are several entry points
which take string arguments (eg. JSTRAN, JRTEXT). Particularly for
the benefit of FORTRAN users, the convention for how to interpret
string arguments has been expanded. In particular, V3 allowed just
two ways for COBOL (eg. ENTER MACRO JSTRAN USING "MYTRAN",TCOUNT or
ENTER MACRO JSTRAN USING TRAN-NAME,TCOUNT where TRAN-NAME appeared in
the DATA DIVISION with PIC X(30)) and only one way for FORTRAN (eg.
CALL JSTRAN('MYTRAN',I)). In V4, these plus several other ways will
be possible (see example below).
DATA TYPE(ARG word,bits 9-12) INTERPRETATION
------------------------------------------------
unspecified (ie. 0) string pointer
FORTRAN LOGICAL data-varying
INTEGER/COMP 5 characters
undefined
REAL/COMP-1 5 characters
undefined
undefined
undefined
REAL*8 10 characters
DOUBLE COMP string pointer
undefined
undefined
COMPLEX string pointer
COBOL string string pointer
undefined
FORTRAN literal ASCIZ
A string pointer is a two-word quantity: its first word is a byte
pointer, and the right half of the second word is the number of
characters in the string. A data-varying string is an actual string
in which the length is stored in the word preceding the string. An
ASCIZ string is a string that is terminated by a 0 byte.
For example, let a data-varying string be used as follows:
LOGICAL DUMARR(7)
EQUIVALENCE (DUMARR(1),DVLEN),(DUMARR(2),TRNAME)
DATA DVLEN/30/
TYPE 101
101 FORMAT(' ENTER TRANSACTION NAME')
ACCEPT 102,TRNAME
102 FORMAT(6A5)
:
:
CALL JSTRAN(TRNAME,I)
DBMS5.DOC Page 24
2.1.7 The Host-language Interface
2.1.7.1 Compile-time/run-time .SCH File Compatibility - The
possibility of compile-time/run-time .SCH file incompatibility will be
made explicit. This will be done by incrementing an edit number
within the .SCH file each time SCHEMA is run and by having
FORDML/COBOL place the value that they see in the argument list of
SBIND. Then at run-time, SBIND will compare the edit-number passed to
it and the actual edit number of the .SCH file. If these two numbers
differ, ERROR-STATUS will be set to " 1500" (usually... see
subsection 2.1.5.4, exception 00 for details).
(Note that INTERCEPT/NOTE can be used to detect this condition, if
that is desired).
2.1.7.2 Record/data Formats in the Host-language - The order of the
data-names in the UWA will always be the same as it is in the schema
DDL. In other words, the calc keys will not be moved to the front of
a record. Also AREA-IDs, DIRECT keys, and ALIASes will not
incorrectly be made part of the record with which they are associated.
Also see subsection 2.2, notes 4 and 5.
2.1.7.3 DBCS symbols that are user-referencable - This set of names
is important for two reasons. It identifies the routines for use in
explicit calls, and it identifies which names the programmer cannot
use for naming his own routines.
A starred (*) name identifies a synonym for the immediately preceding
entry point name. KEY X identifies the negative number associated
with a keyword, as described in section 2.4, note 2. A data base word
(ie. area, set, record, data) refers to the name ID (see section 2.4,
note 1) for the particular data-base-name or the string that would
represent that name (ie. "REC1" for REC1).
CLOSED (KEY ALL)
CLOSED (KEY AREA, area-list)
DELETR (0!KEY SELECT!KEY ALL!KEY ONLY)
FIND1 (record!0, USING-value)
FIND2 (set!0, currency, KEY currency-keyword)
FIND3 (KEY relative, record!0, area!set, KEY AREA!KEY SET)
FINDO (integer, record!0, area!set, KEY AREA!KEY SET)
FIND4 (set)
FIND5 (KEY DUPLICATES!0, record)
GETS (record [,data-list]) ! (0)
*GET
INSERT (record!0, set-list)
*INSRT
MODIF (same-as-GET)
*MODIFY
MOVEC (currency, KEY currency-keyword, result)
OPEND (KEY RETR!KEY UPDATE, 0!KEY PROT!KEY EXCL,
privacy-key, KEY ALL!area-list)
DBMS5.DOC Page 25
REMOVE (same-as-INSERT)
*REMOV
STORE (record)
*STORED
SBIND (schema,edit, subschema,ss-mask, SYSCOM-address)
BIND (record,data-address-list)
EBIND (0,DBMS-NULL)
Additionally, the FINDs and STORE can have appended a SUPPRESS list:
KEY ALL!KEY AREA!KEY RECORD!KEY SET!set,...
The other undotted names are:
SETDB UNSET SAVESS JMNAME
JMAFT JMBEF JMBOTH JMNONE
JBTRAN JSTRAN JETRAN JRSYNC
EMPTY *SETCON MEMBER *RECMEM
OWNER *RECOWN TENANT *RECMO
STATS
2.1.7.4 Validating data aggregates - When the SIZE clause is used in
a data-name entry, the programmer has to tell SCHEMA how much space to
reserve in the host-language's UWA. There are no serious pitfalls
associated with providing extra space, but to protect the programmer
from losing data, DBCS will signal exception 32 when insufficient
space is provided.
(However there is no intrinsic way to determine the size of a
data-name at run-time (without passing a prohibitive additional amount
of information during binding). The best DBCS can do is calculate how
far apart two consecutive data-names are. Unfortunately, when a
referenced name (eg. DIRECT key) is shared between two record types
or a FORTRAN application does not have pseudonyms for all data-names,
data is not necessarily sequential. In other words, the validation
check DBCS makes is negated under these two circumstances.)
2.1.7.5 Loading DBMS applications - DBMS applications are loaded in
the same fashion as any other COBOL or FORTRAN program. This is true
whether or not one is using a private library or a system default
library. For example, .LOAD COBPRG and .LOAD FORPRG, MYFLIB /SEARCH.
2.1.8 The DBINFO utility
This program can be used to dump data from a data base, make a
cross-reference of the names in a sub-schema, and calculate certain
statistical information about the state of a data base.
It is similar to DBMEND in that its command interface is verb oriented
and has the same lexical rules (eg. names containing dashes must be
enclosed with quote marks). Also it shares some of the same
"background" commands since, in both contexts, the user has to select
a schema and open and close areas.
DBMS5.DOC Page 26
2.1.8.1 APPEND/SUPERSEDE commands - This command specifies the
destination file spec for any INFO to be displayed. Its syntax is
simply:
APPEND!SUPERSEDE file-spec
If APPEND is specified, any existing information in the file will not
be overwritten. If SUPERSEDE is specified, the file will be
overwritten.
2.1.8.2 CLOSE command - This command is used to CLOSE one or more
areas that the programmer has OPENed. its syntax is:
CLOSE ALL ! area-name[,area-name...]
2.1.8.3 DISPLAY command - This is the primary action command. Each
time the user gives a DISPLAY command he causes the current INFO
output file to be appended to. The syntax for this command is:
DISPLAY CREF ! MAP ! free ! data ! usage
usage-->USAGE [:set-name]
data -->DATA [:set-name]
free -->FREE [:integer]
If USAGE is not followed by a set-name, the number of record
occurrences for each record type is printed for each object-page (see
2.1.8.6). If a set-name argument is present, each owner record
occurrence which is on an object page is described: the number of
member records on the same page as the owner and the number in the
entire set occurrence are displayed.
If DATA is not followed by a set-name, each record occurrence on an
object page and in the sub-schema is dumped (ie. each of its fields
is displayed). Empty pages do not print any information. If DATA is
followed by a set-name, the NEXT pointers of each object set
occurrenceusage) are followed, and the records are dumped in that
order. A set occurrence is an object of the command if its owner
record is on an object page (see 2.1.8.6).
FREE not followed by an "integer" is equivalent to FREE followed by 0.
DISPLAY FREE will consider any page which has less than "integer"
words free to be full. For each page which is neither full nor empty:
the page number, the count of free words, and some number
(1/10-free-words) asterisks (*) will be printed. Additionally empty
(or full) page-sequences (at least 3 consecutive pages) will be
displayed as "(empty pages) low - high".
The CREF option causes DBINFO to generate an alphabetical listing of
the symbols in the sub-schema: what each is, plus how and where each
is used.
DBMS5.DOC Page 27
The MAP option causes DBINFO to generate a pictorial representation of
each record type in the sub-schema. It shows which words contain set
(and calc) linkages and exactly what user data is in each word. Each
byte of user data is represented by an asterisk. In other words,
there can be at most 6, 5, and 4 asterisks per word in a SIXBIT, ASCII
and EBCDIC record. Conversely, full-word bytes (ie. in computational
numeric items) are represented by one left-justified asterisk.
Lastly, the index associated with each data-name in the map
corresponds to the index printed to the left of its value in the data
dump.
2.1.8.4 OPEN command - This command OPENs each specified area for
PROTECTED RETRIEVAL. Its syntax is:
OPEN ALL![area-name[,area-name]] [:privacy-key]
In other words, it OPENs all areas in the relevant sub-schema or just
those explicitly specified. Each area named (explicitly or
implicitly) in the command must have the same privacy-lock value. The
privacy-key phrase is required only if the areas have a non-null
privacy lock.
2.1.8.5 PAGES command - This command enables the user to control the
pages to which a DISPLAY comand will apply. Its syntax is:
PAGES [range-list]
range-list -->range-tuple [,range-list]
range-tuple-->integer ! integer-integer ! area-name
If no range-list is specified, the range-list is defaulted to the list
of OPEN areas. And specifying an area as a range-tuple is equivalent
to specifying area-first-page - area-last-page. Lastly, specifying a
single integer, say (n), is the same as specifying n-n. In other
words, PAGES' argument is a list of zero or more (maximum 16) page
ranges. For example, PAGES 4,7,13-25 would localize future DISPLAY
commands to pages 4, 7, and 13 thru 25.
2.1.8.6 SCHEMA command - This command identifies the schema file to
DBINFO. Its syntax is simply:
SCHEMA schema-name
2.1.8.7 SS command - This command identifies the sub-schema that will
be the context for DBINFO's evaluation of future DISPLAY commands. It
is an action command; the sub-schema specified will be bound by
DBINFO each time the command is given. (Note: use of this command
does cause the run ID in the .SCH file to be incremented by 1).
DBMS5.DOC Page 28
Understanding this concept is crucial to effective use of DBINFO. By
judicious sub-schema specification, one can precisely control what
record types are DISPLAYed, what data-names within the records are
DISPLAYed, and what areas constitute ALL. The syntax of this command
is:
SS [sub-schema-name]
If the sub-schema-name is absent, the "improper" sub-schema is
identified; that is, the sub-schema which would correspond to the
entire (current) schema. However, repeating this form of the SS
command within one running of DBINFO will merely reset the current
sub-schema to the original "improper" sub-schema.
2.2 Functional Incompatibilities
The list of functional incompatibilities between V3 and V4 of
DBMS-10/20 is as follows:
1. Only 02-data-names can appear in a data-name entry in a
schema, see 2.1.2.2 and 2.1.3.
2. A data-name entry in a schema may not contain a USAGE COMP-x
phrase, see 2.1.2.2.
3. Successful FINDs and STOREs will no longer set up the special
registers AREA-NAME and RECORD-NAME; only the MOVE verb
will--see subsection 2.1.6.2.
4. Calc keys will appear in a host-language program just as they
do in a RECORD/DATA entry in a schema, see subsection
2.1.7.2. (This incompatibility is transparent to all
applications except those COBOL applications that do a MOVE
record-name TO temp-name.)
5. AREA-IDs, DIRECT keys, and ALIASes are declared as 01 names
in COBOL, see subsection 2.1.7.2. This is not truly a change
but a fix for a bug. Unfortunately it affects usage of the
ACCESS statement in COBOL. If you had been passing a
record-name to an ACCESSing subprogram, and expected its
DIRECT key or AREA-ID or anALIAS to be implicitly passed, the
call will have to be altered to make explicit reference to
the ancillary variable.
6. The accessing algorithm for PROTECTED UPDATE will no longer
involve what is called an .RCV file; areas OPEN for
PROTECTED UPDATE will be updated in place. Also if one
program has an area OPEN for PROTECTED UPDATE and another has
it OPEN for RETRIEVAL, the retriever (and/or updater) is
responsible for not getting messed up by the changes the
updater makes. If this is a problem, the retriever should
OPEN for PROTECTED RETRIEVAL. For a thorough discussion of
USAGE-MODEs see subsection 2.1.6.1.
DBMS5.DOC Page 29
7. Sub-schema-names must be unique across any run-unit which
INVOKEs more than one sub-schema. This was already required
for FORTRAN usage and is being generalized for the sake of
simplicity and DBCS efficiency.
8. If the owner of a set is to be SELECTed thru the LOCATION
MODE OF OWNER phrase and its LOCATION MODE is VIA, the SET
entry of the VIA set must precede the SET entry in which the
record in question is the owner. (This sounds much worse
than it is. If one places SET entries that are nearer the
root of a data base structure before SET entries that are
farther from the root, one will never have a problem.)
9. The name (and device and directory) of the .SCH file will be
derived from the (possibly implicit) output file spec given
on the command line to SCHEMA. Earlier versions used the
schema-name in the SCHEMA statement for this purpose--this
name is now ignored.
10. The PRINTA entry point no longer exists within DBCS. Its
functionality is subsumed by DBINFO. (See 2.1.7.3 for the
complete list of V4 entry points).
11. A BINDing failure now returns an exception rather than
EXITing, see 2.1.1.4 and 2.1.5.4.
12. Exception 34 may happen to an existing applications program,
see 2.1.5.4. (The solution is to remove the set-name from
the sub-schema or add the owner record-type to the
sub-schema.)
13. The exception numbers above 30 bear no relationship
whatsoever to what they were in earlier versions, see
2.1.5.4.
14. Privacy locks/keys will be truncated to 5 characters rather
than 6 characters.
15. The exact mechanism for handling REMOVEd/DELETEd currency
indicators in earlier versions is unclear. See subsection
2.1.6.3 for a description of how V4 handles this situation.
16. In cases where a schema-defined name is always syntactically
paired with a keyword designating the type of name it is,
DBCS will ignore the keyword. For example, if one said MOVE
STATUS FOR REC1 RECORD TO X, DBCS would determine that REC1
was a record-name from the its symbol block. In other words,
keywords in this context serve purely as visual documenation.
17. The V4 mechanism for explicitly specifying the buffer count
of an area is described in subsection 2.1.1.5.
18. On a SCHEMA command line, "A." does not == "a.ddl", only "a"
or "a.ddl" does.
DBMS5.DOC Page 30
19. Two statements may not be on the same line in a DDL program.
2.3 Functional Definition of DBMS-V5
2.3.1 V3 --> V5 conversion utility
This utility is a program named V3TOV5--and by definition it will be
useful only to existing DBMS-V3 users. This program is used on-line
by giving a sequence of commands which identifies (by its schema) the
data base to be converted and requests initiation(continuation) of the
actual conversion.
2.3.1.1 Conversion Steps and V3TOV5 Usage - A successful conversion
will always conform to the following sequence of user actions. Also
it is suggested (although not required) that you keep around your old
DDL file and give your V5 DDL program an extension of .ddn until you
have completed your conversion.
1. Read section 4.1. This section contains instructions on how
to change V3 source files into valid V4/5 files. (It is
unlikely any file other than the .DDL file will have to be
changed).
2. Run SCHEMA (V5) and specify the /CONVERT switch:
R SCHEMA SCHEMA-NAME.DDN/CONVERT
This will cause SCHEMA to generate all the files it would
normally generate, but such that the 3rd letter of each
file's extension will be "N". In other words, it would
create a .SCN file and some number of .DBN files. This is
done to facilitate concurrent existence of the old and new
copies of the data base.
3. The actual conversion protocol is as follows:
R V3TOV5 ;START UP THE PROGRAM
SCHEMA schema-name ;IDENTIFY THE DATA BASE
;BEING CONVERTED
TRACE integer ;IF ABSENT, TRACE 10 IS SIMULATED.
;ALLOWS CONTINUATION OF CONVERSION
;AFTER A CRASH BY TYPING
;[COMPLETED PAGE n]
;EVERY integer PAGES.
;ALSO [COMPLETED AREA name]
;MESSAGES ARE TYPED.
PAUSE ;OPTIONAL, IF PRESENT IT CAUSES
;V3TOV5 TO EXIT EACH TIME IT FINISHES
;PROCESSING AN AREA, THEREBY ALLOWING
;THE USER TO DO SOMETHING (EG.
;CHANGE DISKS) BEFORE RESUMING--BY
;TYPING CONTINUE.
DBMS5.DOC Page 31
EXPUNGE ;REQUEST TO EXPUNGE DELETED RECORDS
;(NECESSARY IF THERE ARE ANY
; PARTIALLY DELETED RECORDS IN THE
; DATA BASE--SEE 2.3.1.2.2)
START ;START (OR CONTINUE) EXPUNGE
V3TOV5 ;REQUEST TO MAP V3 DATA
;INTO THE .DBN FILES
START ;START (OR CONTINUE) THE MAPPING
REKEY ;REQUEST TO FORMAT THE NEW DATA BASE'S
;USER-KEY (IE. SORT/CALC) CHAINS
START ;START (OR CONTINUE) THE REKEYING
4. Delete all the old files (ie. the .DBS files and the .SCH
file).
5. Rename *.DBN to *.DBS and schema-name.SCN to schema-name.SCH
2.3.1.2 Understanding the Conversion Process
2.3.1.2.1 Purpose of Multiple Conversion Steps - The conversion
process is divided into phases (EXPUNGE, V3TOV5, REKEY) for two
reasons. The first reason is that the data base will be out of
commission less completely--even though the total time of conversion
is probably increased slightly. This is because the possibility of
interleaving normal usage is much higher than otherwise. The rules
for interleaving normal usage are as follows:
1. During the 1st (ie. EXPUNGE) phase, no normal usage is
possible.
2. After the 1st phase, and until the 2nd (ie. V3TOV5) phase is
started, any accessing other than DELETEs is permitted.
(Note: until the 2nd phase is started the .DBN files are
0-length).
3. During the 2nd phase, and thru the completion of the 3rd
phase (REKEY), retrieval usage-mode is allowed on the old
data base.
(Note: the earliest the old data base can be deleted is
after completion of the 2nd phase).
The second reason for multiple phases is that it achieves isolation of
functional processes:
1. The 1st phase may be omitted by some installations (see
2.3.1.2.2).
2. Only the 2nd phase simultaneously references both the old and
new data bases.
3. Only the 3rd phase requires journaling in order to be
continuable after a crash (see section 2.3.1.3).
DBMS5.DOC Page 32
2.3.1.2.2 Why/when the EXPUNGE phase is necessary - DBMS-V3 and V5
handle record deletion differently. In DBMS-V5, the DELETion of a
record completely eliminates it from the data base. On the other
hand, the DBMS-V3 deletion algorithm will not return the entire space
of a DELETEd record to the free space manager until the record has
been referenced thru each set in which it participates. Until this
has occurred, the remaining part of the record is kept "invisible" by
the mechanism of having its "deleted" flag turned on in its line
header. Consequently before the old data base can be mapped to the
new format, any deleted records must be eliminated from the data base.
Conversely the 1st phase may be omitted by an installation if it knows
that no records in its data base have the "delete" flag on. This is
not a life-and-death decision, however, because the 2nd phase will
detect such records and inform the user that he must execute the 1st
phase before starting the 2nd phase.
2.3.1.2.3 User-data Dbkeys - Any field containing a dbkey must be
described as TYPE DBKEY in the schema because the format of a dbkey in
DBMS-V5 is different than in V3. If the user does not describe such a
field as TYPE DBKEY, V3TOV5 will have no way of knowing that each
occurrence of the datum needs reformatting.
2.3.1.2.4 Adding OWNER IS SYSTEM - If you wish to add new set and
record types to your DDL program, you should wait until after the
conversion process has been completed. Additionally, you should read
section 2.4 in the Data Base Administrator's Manual to understand just
what sort of changes are feasible.
In the particular case that you wish to create a system record (ie.
one or more new member entries specifies OWNER IS SYSTEM) , you will
have to define a new area and designate it as your system area. This
is necessary because DBCS expects to allocate the system record when
an area is accessed for the first time--and there is no way to
simulate that pattern of access during the conversion of an existing
area.
2.3.1.2.5 Hustling - V3TOV5 allows you to operate outside the
prescribed protocol if you feel it necessary. But these more
error-prone activities are isolated here to protect the average
"converter".
1. Any number of new pointers can be added to a record type. In
particular, you might add prior pointers to certain sets to
improve updating efficiency. (IMPORTANT REMINDER: the order
and number of 02-data-names must not be changed however).
2. The REENTER monitor command can be used (in conjunction with
/PAUSE) to control the flow of conversion more closely. For
example, one can do all three steps for a single area by
specifying to /START with that area for each step and doing
REENTER/next-step after each pause.
DBMS5.DOC Page 33
2.3.1.3 Exceptional Conditions - There are certain "bad" things that
can happen during the conversion process. The following subsections
enumerate the known possibilities and describe what the user should do
in each eventuality.
2.3.1.3.1 Recovering from a System Crash - The mechanism for
recovering from an abortion of either the EXPUNGE or V3TOV5 phase is
the same. The mechanism for recovering from the REKEY phase is as for
the other phases plus an additional preliminary step. The critical
parameter during a restart is the last TRACE message printed. It will
contain the last page that is known to have been processed.
Conversely the argument to the TRACE command controls how often these
messages are printed. (Presumably, in a very large data base one
might increase the interval from the default of one message per 10
pages processed.) The recovery scenario is as follows:
1. If aborted during REKEYing,
R DBMEND ;THE DATA BASE RECOVERY UTILITY
CONVERT ;INDICATE THE USE OF .??N FILES
JOURNAL V3TOV5 ;OPEN THE JOURNAL
FORCE ALL ;OPEN ALL AREAS, ;GIVE PRIVACY KEYS IF
ANY
START ;GIVE THE MERGE'S "LEFT" BOUNDARY
END ;...AND THE "RIGHT" BOUNDARY
MERGE BEFORE ;PERFORM THE ACTUAL MERGE
CLOSE ALL ;CLEANUP THE OPEN AREAS TO BE DONE
UNLOAD ;DESIGNATE THAT V3TOV5.JRN ;IS DONE WITH
2. Then for all phases,
R V3TOV5
SCHEMA schema-name ;IDENTIFY THE SCHEMA
EXPUNGE or V3TOV5 or REKEY ;WHICHEVER ABORTED
START last-trace-value ;TO RESUME AT RIGHT PAGE
;ie. restart at 1st page after
;last trace value
2.3.1.3.2 Area or its Page Size Too Small - Except for one
circumstance, the number of pages in a V3 area will suffice in V5.
The exceptional circumstance can manifest itself during conversion if
a V3 area is nearly full and the area contains occurrences of sorted
set types. The circumstance is that the amount of space available
will be inadeqaute for storing each sorted-set index structure during
REKEYing. To correct the problem, either increase the last page of
the area or increase the area's page size. (The comments about
detection and restarting at the end of the next paragraph also apply
here.)
DBMS5.DOC Page 34
Except for one circumstance, the information on a page in a V3 data
base can be mapped into the same or fewer words in DBMS-V5. The
exception is a sorted set in which PRIOR pointers are not explicitly
specified. DBMS-V5 always puts a PRIOR pointer into each record in a
sorted set. Consequently, if an old page is very full and has some
such records, the conversion process would overflow the page. If you
are sure this will happen to one or more of your areas, simply
increase that area's page size to the next 128-word-multiple. If you
do not anticipate this eventuality and it occurs, V3TOV5 will simply
abort with an appropriate message. At this point, you should modify
the appropriate page size(s) of your DDL program (give SCHEMA the
command line "schema-name/CREATE/CONVERT") and restart the V3TOV5
phase from its beginning.
2.3.1.3.3 Improperly Converted .DDL File - Although it is unlikely,
it is possible that you will improperly convert your old .DDL file
into the new format. (It is unlikely because the changes are either
mechanical, such as USAGE COMP to TYPE FIXED BIN, or involve moving
lines into the sub-schema.) The more likely danger is that you will
try to slip an extra change into your schema--in which case you are on
your own. In any event, any flaw in the converted schema should show
up in a widespead fashion. Consequently, after you have renamed the
.??N files to their standard extensions, you should use the DUMP
and/or USAGE commands of DBINFO to validate that the data, as
represented in the new format, is valid.
2.3.1.3.4 Abnormal Abort during Conversion - This situation is
defined by a true abort (eg. ill mem ref), or the V3TOV5 messages
?VTVSAF or ?VTVDAF. Basically, it can be caused by one of three
things.
1. An improperly converted schema. Before retrying, check over
your changes.
2. A spurious monitor error.
3. If the problem persists each time you restart, it must be
assumed you have discovered a bug and the problem should be
reported.
Phase specific restart rules:
1. If aborted during 1st phase, it cannot be schema problem.
Get a fresh copy of your data base and restart the phase from
the beginning.
2. If aborted during the 2nd phase: check the schema, recreate
the .DBN files with SCHEMA, and restart the phase from its
beginning.
3. If aborted during the 3rd phase: delete V3TOV5.JRN, check
the schema, then restart with the 2nd phase--see preceding
rule.
DBMS5.DOC Page 35
2.3.1.3.5 Other V3TOV5 error messages
?VTVDUK V3TOV5 found a sort or calc key in a record that equals
the key in another record, but the schema states that
duplicates are not allowed.
?VTVICS it is not meaningful to repeat a phase or follow it by
an earlier phase (eg. V3TOV5 followed by EXPUNGE).
?VTVNAS you gave a START without preceding it with a conversion
action.
?VTVNMF in processing your old schema, V3TOV5 found an area,
set, record, or data name that is not in your new
schema...correct the discrepancy.
?VTVOOS V3TOV5 detects this condition so as to guarantee its
integrity; just type R V3TOV5 to do more work.
%VTVUFA if the file associated with an area is null or not
found, V3TOV5 will automatically skip that area and
continue with the next one. If the file should have
been found, report the problem or correct your scheam.
?VTVUAJ you have a V3TOV5.JRN file that is in an undefined
state. You should either delete it or run DBMEND as
described in 2.3.1.3.1.
2.3.1.4 Resource requirements - The resource requirements of V3TOV5
are approximately as follows. It statically requires 15K of core and
will expand its core as necesary for area buffers and the in-core
sub-schemas. The average expansion will be on the order of 5K. The
disk space required is phase dependent and is the entire data base:
plus nothing during the EXPUNGE phase, plus a second copy of the data
base during the V3TOV5 phase, plus a 1-transaction journal during the
REKEY phase. However by appropriate use of the PAUSE switch (see
2.3.1.1), you can cause "data base" to be replaced by "area".
2.3.2 Simultaneous Update
DBMS-V5 will allow a user to update (or retrieve) data while another
updates data in the same area/file. It will handle the
valid-copy-of-data problem inherent in this facility thru the
mechanism of the ENQ/DEQ monitor calls.
(Note: the facility relies on the fact that users of a particular
data base all access the same schema).
Four DBMS components control whether and how simultaneous update is
involved in a run-unit's operation.
DBMS5.DOC Page 36
1. It is the OPEN statement which controls whether a run-unit is
within the domain of the simultaneous update facility. The
simultaneous update facility really consists of three
separate OPEN USAGE-MODEs: UPDATE, PROTECTED UPDATE, and
RETRIEVAL. PROTECTED UPDATE is included because a PROTECTED
UPDATER must block out RETRIEVERS (and vice versa). The
three non-simultaneous usage-modes are PROTECTED RETRIEVAL,
EXCLUSIVE RETRIEVAL, and EXCLUSIVE UPDATE. The meaning of
each USAGE-MODE is presented in section 3 sub-section
2.1.6.1.
2. The OPEN JOURNAL statement communicates to DBCS if a journal
will be shared by more than one run-unit -- see 2.3.2.3.1.
3. The IMAGES statement of the DMCL controls the form of
interleaving-unit employed by a data base's applications --
see 2.3.2.1 and 2.1.1.3.
4. The interval between a call to JSTRAN and a call to JETRAN
defines one transaction -- see 2.3.2.1.2.
The following two tables are intended to provide an overview of the
trade-offs involved in using the simultaneous update facility.
THE NON-SIMULTANEOUS USAGE-MODES ARE UNQUESTIONABLY MORE EFFICIENT
THAN THE SIMULTANEOUS USAGE-MODES.
USAGE-MODE WHEN TO USE
-------------------------------------------------------------
RETRIEVAL you intend other run-units to be
simultaneously open for (PROTECTED) UPDATE.
UPDATE use only if you really intend for there to be
simultaneous updaters.
PROTECTED RETRIEVAL use if you expect concurrent retrievers but no
concurrent updaters.
PROTECTED UPDATE use only if you really intend for there to be
simultaneous retrievers.
EXCLUSIVE RETRIEVAL use only if you need to be selfish.
EXCLUSIVE UPDATE use rather than (PROTECTED) UPDATE unless you
really intend for there to be simultaneous
updaters or retrievers.
DBMS5.DOC Page 37
LEVEL OF SIMULTANEITY FEATURES HOW TO ACHIEVE
-------------------------------------------------------------
none inexpensive EXCL RETR!UPDATE
simultaneous retrievers inexpensive PROT RETR
pseudo-simul updaters see F1 see H1
command-interleaving see F2 see H2
transaction-interleaving
with default transactions see F3 see H3
transaction-interleaving see F4 see H4
(F1) Inexpensive but complicates the design/control problem for the
implementor.
(F2) Minimizes blocking time.
(F3) Minimizes blocking time while still accomodating
non-interruptable DML command sequences.
(F4) Minimizes CPU usage and handles non-interruptable DML command
sequences. (Note that F4 and F3 exist on a continuum, rather
than being distinct modes).
***************
H2-H4 apply to all the simultaneous update USAGE-MODES.
(H1) You have run-units that simultaneously open disjoint areas in
EXCLUSIVE UPDATE.
(H2) You optionally define transactions and specify that images are
ordered by command -- see 2.3.2.1.1.
(However if this run-unit did not involve the simultaneous
update facility, specifying images not ordered by command would
be an efficiency consideration -- see section 2.1.1.3).
(H3) You specify that images are not ordered by command and divide
into transactions just those command sequences that require no
intervention -- see 2.3.2.1.2.
(H4) You specify that images are not ordered by command and divide
all the operations of your run-units into transactions -- see
2.3.2.1.2.
2.3.2.1 How Simultaneous? - One makes simultaneous update "work" by
recognizing which microscopic actions of simultaneous updaters cannot
be truly simultaneous. In other words, one defines the ways in which
the operations of two run-units can be interleaved (underline it!).
Thus the amount of simultaneity supported is controlled by the scope
of the resource(s) interleaved upon and/or by the (average) duration
for which a given resource is controlled (ie. the interleaving-unit).
DBMS5.DOC Page 38
Let it be stated without proof that the following (increasing) scopes
of resource are at least plausible: a data base page, a data base
area, or the data base; and that the following (increasing-duration)
interleaving-units are plausible: DML verb/command, user transaction,
or run-unit. However as you decrease the scope of resource
controlled, the potential for two run-units needing resources in a
sequence that will cause deadly embrace is increased. In particular,
a DML verb can manipulate pages in an arbitrary sequence, thereby
making the data base page an unacceptable scope of resource because of
the stigma of deadly embrace. The data base area is an acceptable
scope of resource, but the existing functionality of ENQ/DEQ presently
makes its use unfeasible. (A proposal to correct this will be
generated in a separate memo.) Thus, in DBMS-V5 the only scope of
resource supported will be control of the data base itself, in
conjunction with either a DML command as the interleaving-unit or a
user-specified transaction as the interleaving-unit (or the run-unit
as the interleaving-unit, ie. the three non-simultaneous
usage-modes).
To control which interleaving-unit applies to a particular schema, one
must use the IMAGES statement of the DMCL (see section 3 sub-section
2.1.1.3). In particular, specifying that images are not ordered by
command will result in transactional interleaving; and specifying
that images are ordered by command will result in command-level
interleaving.
2.3.2.1.1 Command-interleaving case - In practice, command-level
interleaving translates to: when DBCS initiates a command, it will
automatically ENQ upon the data base resource (not at all for binding,
STATS, etc.; shared for FIND, GET, and IF; and exclusive otherwise);
and when it completes the command, it will automatically DEQ.
Consequently, even though command-level interleaving guarantees the
physical integrity of the data base, it has one limitation; it gives
one no way to handle the case where a run-unit requires that no one
intervene while it executes several DML verbs that affect a single
desired change (e.g. a passenger wants to change his airplane set
occurrence without being left with no seat at all).
2.3.2.1.2 Transaction-interleaving case - There are benefits to a
large interleaving-unit, particularly in an application in which
simultaneous run-units have a lot of dormant time anyway. One, an
appropriate large unit will enforce the logical integrity of the data
base by preventing intervention for a user-determined period of time.
Two, decreasing the frequency with which a second run-unit manipulates
"your" data base and journal, will decrease the amount of defensive
processing DBCS will have to do (ie. in a CPU usage sense, your
run-unit will operate more efficiently). What should the large
interleaving-unit be? clearly the transaction (ie. use of JSTRAN and
JETRAN). First, user-specified transactions are by definition the
mechanism by which a run-unit defines logical operations on the data
base. Secondly, run-unit interleaving puts a special burden on the
journal processor, so coordinating journaling and interleaving in the
same units has to be a good idea.
DBMS5.DOC Page 39
In practice, transaction-interleaving means that: when DBCS initiates
a transaction, it will automatically ENQ exclusively upon the data
base resource; and when it completes the transaction, it will
automatically DEQ. However commands not executed in the context of an
active transaction (eg. before the first JSTRAN) are handled
specially. Each such command will constitute a default transaction,
and the rules of 2.3.2.1.1 will apply to it. Also if it is an
updating command, it will be given a command header and trailer as
when images are ordered by command. There are two reasons for default
transactions. One, run-units that only retrieve (particularly
existing ones) will not have to be troubled with explicit
transactions. Two, run-units that would like the minimum blocking
time of command-interleaving and wish to contain a few
non-intervenable command sequences, can do this with selective use of
explicit transactions.
There are two exception conditions directly related to
transaction-interleaving. Exception 38 will occur if you call JSTRAN
while a transaction is already active. A LIBOL/FOROTS error will be
signalled if you attempt to do a non-DBMS RETAIN while in the middle
of a transaction.
2.3.2.2 Protection of the current record of the run-unit - It is an
underlying premise of DBMS that all operations on the data base are
done thru one window: the current record of the run-unit.
Consequently, it is necessary that DBCS ensure that a run-unit will
not have its operation confused/aborted because someone else deleted
that record. The implicit philosophy is that the burden of conflicts
should be on those who perform anti-social activities, ie. DELETE.
This protection does exist and is completely automatic, but it does
affect the user's environment as follows.
1. The FINDing run-unit will retain the found record shared if
it is in an area open for UPDATE or PROTECTED UPDATE or
RETRIEVAL. Otherwise it will not retain the found record at
all. It will of course DEQ the old current of run-unit when
a new one is found.
2. When the area in which the current record of the run-unit
resides is closed, current of run-unit is dequeued.
3. If one does a DELETE which eventually tries to delete a
record which is retained by another run-unit, the DELETE is
terminated with exception 40 (ie. resource not available).
DBMS5.DOC Page 40
2.3.2.3 New Journal-related Functionality
2.3.2.3.1 Shared Journals - If two run-units are updating the same
area simultaneously, they obviously are also updating the journal file
simultaneously. When a journal is shared like this, several things
must be periodically done to it to ensure its continuing integrity.
And the cost of that work makes it imperative that a run-unit
communicate to DBCS when its journal need not be shared.
Consequently, before OPENing any areas, the run-unit should execute
the following statement:
OPEN JOURNAL USAGE-MODE [EXCLUSIVE] UPDATE.
The EXCLUSIVE keyword should be absent if and only if the run-unit
will be backing up one or more areas OPENed with USAGE-MODE UPDATE.
Although its use is suggested, it must be legal to omit an
open-journal statement so that existing DBMS programs will not be
impacted. So the following rules apply when a open-journal statement
has not been executed by the time the first updating open is
attempted. If the area is being opened for exclusive or protected
update, an OPEN JOURNAL USAGE-MODE EXCLUSIVE UPDATE will be simulated.
Conversely an OPEN JOURNAL USAGE-MODE UPDATE will be simulated if the
area is being opened with USAGE-MODE UPDATE.
A secondary benefit of the OPEN JOURNAL statement is that it can be
used to force open the journal even when only temporary areas are to
be opened. Previously this situation was a problem because usage of
JSTRAN, JRTEXT, etc. could not be checked out conveniently when it
applied.
2.3.2.3.2 Journal lifetime - When a run-unit opens a journal, DBCS
must decide whether it should append to the journal, start anew and
overwrite the journal, or abort because the journal is in an undefined
state.
DBCS will overwrite the journal only if it is in a done-with state. A
journal is done-with if the images in it have already been merged (see
2.3.2.3.3), or you have indicated that all run-units have successfully
completed. You indicate this via use of the CLOSE JOURNAL statement
(as opposed to CLOSE RUN-UNIT). If you are the last/only run-unit
active when you do a CLOSE JOURNAL, DBCS will alter the journal's
label page to indicate that the journal is done-with. Otherwise CLOSE
JOURNAL will be equivalent to CLOSE RUN-UNIT. Also both CLOSE
RUN-UNIT and CLOSE JOURNAL will be equivalent to CLOSE ALL if no
journal is open when either is called.
DBMS5.DOC Page 41
If a journal is not in a done-with state, DBCS will append to it if
the journal's label page correctly represents the current state of the
journal. Otherwise it will abort with exception 61. A journal's
label page is made to correctly reflect the state of the journal by
CLOSE RUN-UNIT, CLOSE JOURNAL, and at the end of every
interleaving-unit in a run-unit in which the journal is shared. Thus
exception 61 will occur only when you have previously aborted one or
more updating run-units and not merged the images they generated back
into the data base -- see 2.3.2.3.3. (Note: DBCS never supersedes
the journal (for efficiency reasons). So if the journal somehow gets
clobbered -- ie. DBCS generates exception 61 or 63 when it should
not--simply delete the journal.)
2.3.2.3.3 Changes to DBMEND and the journal file - The most obvious
change is that the journal must contain run-unit IDs so that the
changes of a particular run-unit can be isolated when you are using
DBMEND; and conversely DBMEND must have semantics for denoting
run-unit IDs:
1. The form of a boundary indicator goes from "[name:] index" to
"[name:] index [(run-unit ID)]".
2. If a run-unit ID is absent from a boundary indicator, DBMEND
ignores the run-unit IDs in the journal when attempting a
boundary match.
3. The run-unit ID in a completely unshared journal is 0.
However, the "journal characteristics" message generated when
a run-unit opens a journal will indicate in any event the
run-unit's ID. The form of the message is:
[JOURNAL CHARACTERISTICS ARE:]
RUN-UNIT ID id-value
schema-name RUN schema-run-of-last-overwriter
date/time-journal-last-overwritten
4. An abstract will show which run-unit generated any
transactions, text, and commands displayed if you specify the
RUNUNITID option to the DISPLAY command.
(Note: the addition of the run-unit ID plus expansion of the journal
label means that V4 journal files will not be processable by
DBMEND-V5; however there is nothing to prevent one from using
DBMEND-V4 to merge V4 journal files).
(Note: because a journal can now contain updates of different
run-units, it may no longer be sorted by command index and each
transaction index. Thus DBMEND will no longer be able to determine if
current journal position is "past" the first-processed boundary except
by encountering beginning/end of journal before it encounters the
boundary).
DBMS5.DOC Page 42
Two other changes to DBMEND relate to placing the journal in a
done-with state. Specifying the /UNLOAD switch for a disk journal
will place it in a done-with state. Specifying the /COMPLETE switch
(see 2.3.2.3.4 as well) for a magtape journal will place the journal
(temp file) in a done-with state.
To achieve the DBMS-V3 effect of a /COMPLETE switch (ie. journal
truncation), specify COMPLETE jpage. This will cause a POSITION jpage
followed by placement of an EOF marker after that page.
2.3.2.3.4 Magtape journaling - (The program DAEMDB is described in
2.3.2.3.5).
Magtape journaling works as follows. DBCS will initiate magtape
journaling if any of the conditions in the next paragraph are
satisfied. It initiates magtape journaling by (1) using IPCF to
communicate to DAEMDB the MTA unit which is to be the journal and (2)
opening a file called DSK: journal-name.JRNrest-of-spec. This file
is an ordinary journal file other than for the fact that DAEMDB is
aware of its existence--and from DBCS's point of view it is the
journal.
If any of these conditions are satisfied, magtape journaling will be
initiated.
1. DEVCHR of the device in the journal file spec (see section
2.1.1.2) has magtape characteristics.
2. If the device in the journal file spec is not associated to
an actual disk device and the text of the device is "MTA",
magtape journaling will be initiated on the magtape unit the
operator chooses.
However if the magtape service is unavailable, you are given the
opportunity to select disk instead. Unless you have a USE
condition for 0946, DBCS exits after typing:
%DBSODJ ONLY DISK JOURNAL FEASIBLE (DAEMDB CODE xxx)
You should then (give up or) ASSIGN/DEFINE the journal name to a
disk device and then type CONTINUE. If a DBCS-caused exit is
incompatible with your application, you should have created a USE
condition for 0946 and have made the USE procedure:
CALL JMDISK ...merely makes journal device "DSK"
OPEN the journal as before
IF error-status not = 0 then abort presumably to get a disk
journal.
(Note: if a DBCS software error is not an issue, also associate this
USE procedure with exception 0967).
DBMS5.DOC Page 43
The DAEMDB-interaction codes are:
0 success, the message will not occur
1 DAEMDB unavailable (SHUTDOWN already given)
2 magtape could not be opened
3 unable to open journal temp file
4 improper device type after ASSIGN/DEFINE
5 DBCS software error during initialization
6 JMDISK already done once
7 DAEMDB already managing 8 journals
Also the generality of journal device selection is somewhat restricted
under TOPS-10. If your journal device on the DECSYSTEM-10 were JRN:
for instance, you would be pretty much restricted to having a disk
journal. You would have to be able to gain control of MTAn in order
to ASSIGN MTAn JRN; whereas on the DECSYSTEM-20 DEFINE JRN: MTAn:
would allow you to specify MTAn without your job having control over
it.
The run-unit and DAEMDB interact in essentially the same way as two
concurrent updating run-units; each maintains knowledge of the state
of the journal (temp file) by reading and updating the journal's label
page as necessary. And as when a run-unit opens an area (or the
journal) with USAGE-MODE UPDATE, the run-unit will automatically
follow the applicable rules of 2.3.2.1 and retain the data base for
the duration of each interleaving-unit. Conversely DAEMDB does its
work by periodically copying the information in the journal temp file
to magtape and then retaining the data base ONLY LONG ENOUGH TO MAKE
THE JOURNAL LABEL PAGE INDICATE THAT DBCS CAN START WRITING TO THE
BEGINNING OF THE JOURNAL FILE AGAIN.
Because DAEMDB/run-unit interaction is interleaved, the cost of
magtape journaling is nearly the cost of operating with a journal
opened with USAGE-MODE UPDATE. Thus the cost of magtape journaling
for a single updater is somewhat greater than the cost of disk
journaling for a single updater. However the cost of magtape
journaling and disk journaling is approximately the same for
simultaneous updaters.
Just as with a shared journal, it is the user's responsibility to
guarantee that the protection of the journal temp file is such that
each accessing run-unit can update it. Note also that the name and
location of the journal temp file is established simply by replacing
the device field of the user specified journal spec with DSK. Thus
the JOURNAL statement of the DMCL gives the user complete control over
the name and characteristics of the journal temp file.
DBMS5.DOC Page 44
There are some beneficial side-effects to the fact that the journal
temp file is an ordinary disk journal and that DAEMDB is a background
task. First, when DAEMDB reaches end-of-reel on a magtape, there is
no pause in user processing--the run-unit's journal temp file simply
grows a little bigger than usual before it is copied to magtape and
truncated again. Second, if DAEMDB aborts for some bizarre reason,
your run-unit will not be impacted--it will simply become a disk
journaler in effect. Third, the magtape part of the journal need not
be involved at all in your use of DBMEND if the images which are
relevant are all still in the journal temp file--in this case, you may
simply specify the journal temp file spec (see /UNLOAD in 2.3.2.3.3)
to the /JOURNAL switch rather than the magtape spec and proceed as
usual. (IMPORTANT NOTE: keep in mind that journal page two of the
journal temp file, its first data page, is actually at an arbitrary
point in the permanent journal. In other words, to get an abstract of
the journal temp file, you must "/posit 2" so that DBMEND will know it
must follow "middle of the journal" protocol when initializing the
abstract). Fourth, magtape management messages are not seen by
application programs. Only the job controlling DAEMDB sees new-reel
messages or magtape errors reported.
When you do wish to have DBMEND operate on a magtape journal, the
following rules should be observed. One, give the /JOURNAL the same
file spec that was given by the aborted run-unit(s) so that DBMEND can
automatically locate the journal temp file as well. Two, do not
forget to give a /REELS command if this is a multi-reel journal.
Three, if not all the data in the journal temp file has been copied to
magtape (eg. the system crashed while your run-unit was active),
specify the /COMPLETE switch to cause DBMEND to merge any unmerged
journal temp data with the magtape journal. (Note that this will
place the journal temp file into the done-with state). Four, proceed
as with a disk journal.
You must be aware of the nature of the /COMPLETE algorithm to the
following extent. DBMEND backspaces three journal pages and simulates
a /POSITION "page the 1st journal-temp-file-page will be". If the
magtape is in a random position, this operation may fail. However you
can guarantee success of this positioning by simply doing a /REWIND
before the /COMPLETE.
2.3.2.3.5 The background MTA journal processor - DAEMDB is simply a
utility to copy data from one or more journal temp files to a matching
set of MTA journals. It runs as a background task concurrently with
application run-units and can be run under OPSER/PTYCON or as an
ordinary time-sharing job.
DBMS5.DOC Page 45
Application jobs have to can communicate with it via IPCF when opening
or closing the journal--and can because the IPCF name "[SYSTEM]DAEMDB"
is reserved to it. During an OPEN, the application waits until it
receives a message back from DAEMDB before continueing. Note that
this waiting period includes the time for the operator to mount the
tape unless another apllication has already started or a /CREATE was
done at the DAEMDB terminal. Similarly on a CLOSE, the application
waits when it does a "real" CLOSE JOURNAL. Also during a CLOSE
JOURNAL, DAEMDB unloads the magtape and eliminates the journal from
its table of journal. CLOSEs when someone else still has the journal
open merely cause some trivial accounting to occur. Finally, a CLOSE
RUN-UNIT, when you are the only run-unit, copies all the currently
remaining data from the journal temp file but leaves the magtape open
and the journal in DAEMDB's table of journals.
To initialize DAEMDB as an ordinary timesharing job, just login and
type R DAEMDB. To run DAEMDB under OPSER, give this sequence of
commands to OPSER:
:SLOG 1/2
:DEF DB=
DB-R DAEMDB
To run DAEMDB under PTYCON, give this sequence of commands (the $ is
an altmode):
DEFINE $DB
DB-LOG OPERATOR ANY a-number
DB-DAEMDB
DAEMDB relies heavily upon the schema name associated with each of the
journals it is managing. The reliance is realized in terms of volume
ids. A volume id tells the operator/DAEMDB user which magtape to
mount, and it will conventionally be of the form "aaaabb" so that the
operator can use pre-labeled tapes. the "a"s are the first letters of
the schema name and "bb" is the current reel number. Thus if your
installation supports multiple schemas their initial letter sequences
must be different. As well as identifying tapes for the operator, the
volume id tells DAEMDB (in ABORT, CREATE, MOUNT, RETRY) which of the
"many" journals it is managing to make "current". Thus volume ids are
optional only if DAEMDB can identify the journal from an immediately
preceding prompt it typed.
The operation of DAEMDB is controlled by the following switches. Any
unique abbreviation is acceptable except for ABORT, EXIT and STOP --
these must be spelled out. When DAEMDB is started, it presumes it
just did a polling and goes to sleep for the default polling period
(=100 seconds). However, whether DAEMDB is active, sleeping, or in
TTY wait, any switch will be processed when it is presented to DAEMDB.
The switches are as follows.
DBMS5.DOC Page 46
SWITCH FUNCTION
-----------------------------------------------------------
ABORT [dev:][volid] DAEMDB has requested an operator action in
response to EOT or a magtape error, and the
operator has decided that processing of the
magtape portion of this journal should be
stopped. The device is for clarity only.
CREATE dev: volid Pre-associate a magtape to its journal's
schema. No application requesting this
journal will experience a real-time wait
while the operator mounts his tape. Of
incidental note: DAEMDB will not actually
know the schema name until an application
starts up...it will only know it
approximately via the volume id.
CURRENT Type out the current setting for each mode.
This is basically a debugging switch.
EXIT Exit to the monitor after clearing all active
queue requests. Do not allow a CONTINUE.
GO Continue after a STOP
HELP Print this table
MOUNT [dev:][volid] The operator has mounted a new magtape on
dev: (or the device in the prompt if dev:
is absent). Note that MOUNT and ABORT are
"antonyms".
POLL seconds Define and initiate a new polling period.
DAEMDB will sleep for n-seconds or until it
has something to do. The default polling
period is 100 seconds. (It is the journal
temp files which are being polled for
uncopied data).
RESET Simulate starting DAEMDB--with one
difference--the existing table of journals
remains intact. It is difficult to predict
whether this switch is useful, but the intent
is to give the operator a means of getting
DAEMDB back to a defined state without losing
its table of journals.
RETRY [dev:][volid] Tells DAEMDB to ignore the error it reported
and repeat the operation that failed. The
device would be specified for clarity only.
This command prevents DAEMDB from
unnecessarily aborting after a spurious I/O
error such as something going temporarily
off-line.
DBMS5.DOC Page 47
[NO]SHUTDOWN Tell DAEMDB to not accept any new journals
and to do an EXIT when all of the active
magtape journals have been closed by the
users. Prefixing NO takes DAEMDB out of a
SHUTDOWN state, ie. it will accept new
journals.
STOP Return to DAEMDB command level immediately.
The operator would presumably use this switch
to give him time to fix a magtape or some
such problem.
THRESHOLD pages Tells DAEMDB to bother to copy and truncate a
journal temp file only if it is at least
n-pages long. The default threshold is 50
journal pages.
WHAT Type the state of each journal DAEMDB is
managing.
DAEMDB does an "action prompt" when a magtape is initially opened and
each time the current reel of a journal must be replaced. The prompt
is: [ACTION REQUIRED FOR VOLUME volid ON mta]. Also, the prompt may
have been preceded by a magtape or journal temp file error message.
In any event, you should respond with either the /MOUNT or /ABORT or
/RETRY switch as appropriate. Note that the prompt always refers to
the current reel (via the volid), so that to mount a new volume you
should explicitly give the volume id when you do the /MOUNT. Finally,
in order to protect against partially copied sequences that span
reels, DAEMDB types a message when the first copy-sequence has been
completed on a new reel. In other words, when a reel is being
replaced, its replacement should not be considered part of the journal
until DAEMDB responds with [VOLUME volid NOW INITIALIZED].
2.3.2.4 Guarding Against Non-cooperation of Run-units - There are
forms of non-cooperation that are not detectable except from long-term
side-efects. As noted, DBCS can guarantee the physical integrity of
the data base, but only you can ensure world-view consistency.
However the following forms of non-cooperation are either detected by
DBCS or declaratively inhibited.
(Declarative Restraints)
1. There is one journal per schema unless a run-unit explicitly
circumvents this by calling JMNAME.
2. The IMAGES statement provides inherent co-ordination of
journaling and run-unit interleaving.
(Procedural Constraints)
3. If you attempt to open an area with USAGE-MODE UPDATE and
already have OPENed your journal exclusively, exception code
0938 will be returned.
DBMS5.DOC Page 48
4. If you have a shared journal, the only way in which you can
use JBTRAN is as follows: in transaction mode and with an
argument of 0. Otherwise, exception code 1645 is returned.
There is one "special" form of non-cooperation. If an updating
run-unit aborts abnormally, other run-units are "in danger" of
accessing a data base which is potentially in an undefined state.
However it is only an illusion for a very simple reason. So long as a
RESET is not done by the aborted job, all the locks it had in place to
prevent trespass are still in place. Thus, if the site does not panic
by allowing a RESET to be executed by the aborted job, it will have
all the time in the world to evaluate the situation and react
accordingly (eg. terminate all the run-units and restart entirely, do
a RESET because the aborting run-unit did not injure the integrity of
the data base).
2.3.3 Miscellaneous Changes
2.3.3.1 Unrounded Logical Page Size - Before V5, each page size
specified in the DMCL was rounded up to the next monitor-defined unit
of disk storage (ie. 128-word multiples on the 10 and 512-word
multiples on the 20). However this is not strictly necessary...the
physical page size must be such a multiple, but there is no reason why
the logical page size cannot be as was specified in the DMCL.
Additionally there are two reasons to support this distinction: (1)
it enables a site to account for data expansion by filling an area in
layers (ie. by gradually increasing page size) (2) as implied in
section 2.3.1.3.2, it would make a general purpose conversion utility
somewhat easier to use.
This feature does not impact existing data bases; the effect of
unrounded logical page sizes is felt at precisely one time only, when
a new record is stored.
2.3.3.2 Specifying a Limit to Journal Size - The JOURNAL statement of
the DMCL has been extended to provide you a means of preventing a disk
journal from growing to an arbitrary size. By appending,
SIZE [IS] integer [TRANSACTIONS]
to the end of a JOURNAL statement, you will cause DBCS to reposition
its journal file pointer to the beginning of the journal after every
(integer)th transaction. Thus, a site could use this feature if its
situation is such that it knows it will never need to backup a data
base more than (integer) transactions. This clause applies to any
run-unit that has a disk journal which is either unshared or for which
images are not ordered by command.
(Note: a secondary benefit of this feature is that disk journal
efficiency is improved because it is cheaper to rewrite a journal page
than to extend a journal.)
DBMS5.DOC Page 49
2.3.3.3 /CONVERT switch for SCHEMA and DBMEND - The /CONVERT switch
has been added to support V3TOV5 and to lay the groundwork for a
general purpose data base redefinition utility.
/CONVERT tells SCHEMA to generate .DBN files and a .SCN file rather
than .DBS files and a .SCH file.
Conversely /CONVERT sets DBMEND to process .??N files and /NOCONVERT
returns DBMEND to its normal mode. When you need to use a [NO]CONVERT
switch, it should precede the JOURNAL or (SCHEMA) switch and all OPENs
so that all relevant files will be processed in the correct/same mode.
2.3.3.4 UNANTICIPATED as an INTERCEPT option - If one specifies
INTERCEPT (or NOTE) UNANTICIPATED EXCEPTIONS, all exceptions other
than 307 and 326 will be intercepted (or noted). The purpose of this
option is to suppress interception only for those exceptions which are
(normally) used to control program flow.
2.3.3.5 The /UNFLAGGED switch for FORDML - This switch allows a
FORDML user to (optionally) omit the "* DBMS" line for single-line DML
statements, provided no other line in the program has "period" as its
last non-blank non-remark character. The purpose of this switch is to
allow for smaller, more readable FORDML programs at the price of
conforming to one additional lexical rule.
2.3.3.6 The USE statement - It has been made easier to associate a
variety of exceptions with a USE procedure. Generic exception codes:
one can specify xx00 to associate the procedure to any exception for
statement "xx". Generic statement codes: one can specify 00yy to
associate the procedure to the exception regardless of the executing
statement. Grab bag procedure: USE ERROR-STATUS. will cause
application of its procedure to each exception which is not covered by
an earlier USE statement in the program (conversely any USE statement
after this statement would be a no-op).
2.3.4 Summary of Environmental Changes
The following keywords have been added to the DML: JMDISK (a
user-callable entry) and JOURNAL. The following keywords have been
added to SCHEMA: TRANSACTIONS. The /CONVERT switch has been added to
SCHEMA and DBMEND. Exceptions 46, 65, 66, and 67 have been added.
Exceptions 38 have been given a different definition. Exceptions 31,
40, 45, 61 and 63 have been given more general meanings. See section
2 subsection 2.1.5 for the updated exceptions table.
DBMS5.DOC Page 50
3.0 KNOWN BUGS AND DEFICIENCIES
1. A DBMS applications program cannot be restarted by the
ctrl-C/START sequence; one can only RUN (GET/START) a DBMS
program.
2. If the CLOSE statement signals an exception, the state of the
system will not be backed up to what it was before the CLOSE.
3. Explicit SFD's are not supported in file specs.
4. No .DBS file (ie. DBMS-10 area) may have a page range such
that it could grow to larger than 256,000 disk blocks (one
block=128 words).
5. The word DBMS is a reserved word in the COBOL compiler, but
this fact is not properly documented nor properly flagged as
an error.
6. User symbols in an INVOKE or ACCESS statement constitute user
variables as far as the COBOL compiler is concerned.
Therefore they may not be declared anywhere else in the DATA
DIVISION.
7. If exception 03 (data-names from wrong record) occurred
during a GET, the UWA may not be left the same as it was
before the verb was executed.
8. An area cannot be simultaneously OPEN twice (ie. by two
sub-schemas of the same schema) in a run-unit.
9. Floating point numbers cannot be dumped by DBINFO on a KA10.
10. COBOL and FORTRAN program-units both containing DML
statements cannot be mixed in the same load-unit because the
form of the special registers is different in COBOL and
FORTRAN.
11. The "name" special registers (eg. ERROR-RECORD) cannot be
simply compared to COBOL literals because the former are
ASCIZ strings (to facilitate displaying them). To accomplish
the comparison, do an EXAMINE LOW-VALUES TO SPACES to the
string.
DBMS5.DOC Page 51
4.0 INSTALLATION INSTRUCTIONS
To install DBMS-10, follow the instructions below:
1. To place DBMS-10 on SYS:, follow this procedure:
a. Mount the DBMS-10 distribution tape (marked QH101) on
MTA0:, and type the following commands:
R BACKUP
TAPE MTA0:
REW
INTERCHANGE
DENSITY installation-dependent
RESTORE SYS:*.*=DSKB:[10,6]*.EXE
REW
RESTORE SYS:*.*=DSKB:[10,6]*.HLP
REW
^C
2. To prepare to (re)load DBMS-10 (or parts thereof):
a. Mount the DBMS-10 distribution tape (marked QH101) on
MTA0:, and type the following commands:
R BACKUP
TAPE MTA0:
REW
INTERCHANGE
DENSITY installation-dependent
restore *.*=dskb:[10,6]*.*
rew
^c
The components of the DBMS package, are as follows:
SCHEMA
FORDML
COBOL interface
DBCS
DBMEND
DBINFO
DAEMDB
4.1 Converting Existing Applications
There is an inherent overlap between this section and section 2.3.1
since V3TOV5 is really a utility to facilitate installation of DBMS-V5
by version 3 sites--rather than a software product. Accordingly this
section attempts to explain where V3TOV5 fits into the installation
procedure, while section 2.3.1 explains in detail the steps involved
in using it.
DBMS5.DOC Page 52
Steps to convert your V3 data base:
1. Section 2.2 should be read carefully, and application source
files should be changed to reflect the incompatibilities
described there.
The primary change is to the schema DDL data-name entry, and
involves changing USAGE COMP... to TYPE... and moving all
text (ie. 03 names) into the appropriate sub-schemas.
The only DML change that is likely to cause any source
alterations at all is that successful FINDs and STOREs no
longer set up AREA-NAME and RECORD-NAME...the MOVE statement
must be used instead.
2. Read section 2.3.1 on how to use V3TOV5.
However if you intend to reload rather than convert, just
delete your DBS files and SCH file and translate your
converted DDL program with SCHEMA V5 before running your
reloading program.
3. The host-language interface has changed. Existing programs
must be (re-preprocessed and) recompiled with the COBOL
and/or FORTRAN systems built from this tape.
4.2 Configuring the System Software
1. DBMSn0 is shorthand for DBMS10/DBMS20.
TOPS-10 sets should read it as DBMS10
TOPS-20 sets should read it as DBMS20
2. If COBOL support is desired:
a. Read COBOL.MEM in the 1st save set of the COBOL
distribution tape (marked QH504). It will explain how to
place LIBOL.REL AND LIBSHR.REL onto disk.
b. Make sure that your non-DBMS copy of LIBOL.REL and
LIBSHR.REL are in the directory from which DBMSn0.CTL
will be submitted.
3. If FORTRAN support is desired:
a. Read FORTRA.MEM in the 1st save set of the FORTRAN
distribution tape (marked QH500). It will explain how to
place FORLIB.REL onto disk.
b. Make sure that your non-DBMS copy of FORLIB.REL is in the
directory from which DBMS10/20.CTL will be submitted.
DBMS5.DOC Page 53
4. Read DBMSn0.CTL.
a. In particular, there are DEFINEs (TOPS-20) and ASSIGNs
(TOPS-10) at the beginning of the CTL file. Alter the
logical assignments therein as necessary for your site.
b. To load just the OTSs, do this submit:
SUB DBMSn0/RES/TIM:15:.
To load all the non-OTS components as well, do this
submit instead:
SUB DBMSn0/RES/TIM:30:/TAG:DBALL.
c. If execution of DBMSN0.CTL should abort, you should
reperform steps 2b and/or 3b before repeating step 4b.
5. Copy the built host systems to SYS:
LIBOL.REL to SYS:LIBOL.REL
Cdbots.exe to SYS:LIBO11.EXE
and/or
FORLIB.REL to SYS:FORLIB.REL
FDBOTS.EXE to SYS:FOROTS.EXE
6. Copy *.HLP and *.EXE from the 2nd save set of the DBMS tape
to the appropriate system device.
7. If support of MTA journaling is desired and you wish to run
DAEMDB under OPSER/PTYCON, insert at least these commands
into your system-restart auto file (see 2.3.2.3.5 for how to
setup non-defalt values for DAEMDB's controlling parameters):
For TOPS-10:
:SLOG 1/2
:DEF DB=
DB-R DAEMDB
For TOPS-20 (the $ is an altmode):
DEFINE $DB
DB-LOG OPERATOR ANY 77777
DB-DAEMDB
If you wish to run DAEMDB as an ordinary time-sharing job,
simply login a job and type R DAEMDB each time your system
starts up.
IMPORTANT: for the time being at least, one must pre-assign
magtapes to the DAEMDB job on TOPS-10. To do this, simply do
1 or more MOUNT commands before typing R DAEMDB.
DBMS5.DOC Page 54
8. DBMS-V5 utilizes the ENQ/DEQ facility. Consequently you
should ensure that your system is configured such that
sufficient monitor free space is available to your DBMS
users, and that each DBMS user has global-ENQ capabilities
and an adequate ENQ quota. For TOPS-10 use REACT to set
quotas and capabilities (ENQ capability is bit 11 (ie.
100,,0) of the capabilities word). For TOPS-20, use ^Ecreate
to set ENQ capability. Also, see ENQ/DEQ in the monitor
installation guide. As regards quantifying your needs, they
are approximately: 2 locks for each open area plus 2 locks
per run-unit.
9. If magtape journaling is desired, the comments regarding
ENQ/DEQ apply to IPCF as well. As regards quantifying your
needs, they are approximately 1 send and 1 receive for each
application run-unit; and (n) sends and receives for DAEMDB,
where (n) is the number of simultaneous magtape journalers.
5.0 INTERNAL CHANGES
The list of internal differences is not truly ordered, but there is
some attempt to group the DML changes and to group the file-affecting
changes. Except where noted, these notes are differences between V3
and V4 (or V5). Differences between V4 and V5 are noted individually.
1. In earlier versions each reference to a record, area, data,
or set name in a DML statement would cause a character
string, representing the name, to be passed to DBCS. For
example, GET REC1 would have translated to CALL GET('REC1')
in FORTRAN and ENTER MACRO GET USING "REC1" in COBOL. In
version 4, the reference to REC1 will be replaced by an index
into a table (assigned during schema processing), rather than
a character string.
However if the user wishes to explicitly call a DBCS entry
point, he may still pass a string--which will be dynamically
converted to its table index. In other words, although
FORDML(or COBOL) will generate CALL GET(integer), the user
can still code CALL GET('REC1') in his programs. However,
this string processing ability applies only to record, set,
and area names--and not to data-names because data-names are
simply not maintained internally at run-time.
DBMS5.DOC Page 55
2. Similarly, keywords such as NEXT were passed as character
strings. These are now passed as negative numbers (to
distinguish them from the table indexes) and are as follows:
KEYWORD CODE
----------------------
ONLY -10
SELECTIVE -11
FIRST -12
LAST -13
PRIOR -14
NEXT -15
DUPLICATES -16
ALL -17
AREA -18
RECORD -19
SET -20
UPDATE -21
RETRIEVAL -22
RUNUNIT -23
PROTECTED -24
EXCLUSIVE -25
RESERVED -26
RESERVED -27
JOURNAL -28 (V5 only)
When a keyword is expected, a 0 argument indicates a default
(or absent) keyword. And the argument indicates an absent
user-name when a name is expected.
3. An indexed sequential access method will be used to add
members to and to search sorted set occurrences. This will
greatly speed up STOREs, INSERTs, and MODIFYs that access
sorted sets. The index structure will be a B-tree in which
each index block is big enough to contain 16 sort-key/dbkey
pairs, unless 16 keys would require more than 120 words. In
this circumstance, the index block size will be n*pair-size
where (n) is such that the product is as near as possible to
120 and still less than 120.
4. The DELETE verb will always completely delete any record that
it processes. In other words, the record will be removed
from each set it is in and all space associated with the
record will be returned to the free pool.
DBMS5.DOC Page 56
5. FIND integer of SET/AREA will no longer generate a call to
FIND3. Instead it will generate a call to the new entry
point, FINDO.
6. The FUNCT. OTS interface facility, created to support LINK
overlays, will be used by DBCS for its own OTS interfacing.
FUNCT. is documented in an appendix of the LINK manual.
7. The format of an after-image directory file (.RCV files were
an example of this type of file) has been changed slightly.
The first (n) pages of an area .TMP file are the directory,
and there are PAGESIZE*2 entries per directory-page (ie. 18
bits per entry). Thus n=!PAGERANGE/PAGESIZE*2!. The entries
are arranged such that the left-half of the first word
contains the first page pointed to by this directory-page,
the left-half of the 2nd word contains the 2nd page, and so
on... thus the right-half of the first word of the
directory-page points to the (PAGESIZE + 1)th page.
Also, the mechanism by which .DBS files are extended in V4 is
such that unreferenced pages will not be placed in the area
.TMP file. Thus temporary areas are now ideal for debugging
when calc records (which arbitrarily extend .DBS files) are
involved.
8. The symbol blocks in a .SCH file and those created during
BINDing are somewhat different than they were in earlier
versions. (A complete description of each type of symbol
block will appear in the version 4 manuals--and does appear
in the UNV source file DBSDCL.MAC, which is on the
distribution tape.)
9. The format of a page in a .DBS file has been changed to
improve record accessing efficiency (and generalized to
support multiple calc-chains per page). The format is as
follows (where PAGESIZE is p):
word 0: page-number
word 1: i ! j
n words: calc-chain pointers
word n+2: data word
:
:
word j-1: last data word
(word j thru word p-i-1 are not in use)
word p-i: see DBSDCL!offset of record i
:
:
word p-1: see DBSDCL!offset of record 1
DBMS5.DOC Page 57
The value (i) is the highest record number ever used on this
page. The value (j) is the offset of the first word which
does not contain data. The value (n) is 0 or more and is the
integer given in the CALC RPP clause in the ASSIGN statement
for this area. Word p-1 back thru word p-i are the line
headers of line-1 thru line-i. For details, see PH.* and
LH.* in DBSDCL.MAC.
10. The 128-word prefix sector has been supplanted by the area
status record, see subsection 2.1.5.3.
11. The ENQUEUE/DEQUEUE facility, rather than reader counts, is
used in version 4 to control concurrent access to an area.
Note that this means that retrieval-only areas no longer have
to be protected <022>.
12. All system processed strings will be represented in ASCII
(rather than SIXBIT), ie. the relevant special registers,
AREA-IDs, and privacy locks.
13. [V5 only] Journal page headers have been expanded from 4 to 6
words and logical blocks have been expanded to 3 words, both
to accomodate simultaneous update. The make-up of these
headers is detailed in DBSDCL.MAC.
Because this is such a complicated upgrade, no bug fixes will
be described. We wish this upgrade to consolidate DBMS.
6.0 SUGGESTIONS
None.
[End of DBMS5.DOC]