This section provides programming guidelines for using Adabas Vista with Adabas:
If an Adabas file is defined as a standard Adabas Vista partitioned file, each Adabas ISN is modified with a partition identifier before returning the ISN to the application. Such a modified ISN is called an Adabas Vista ISN. Correspondingly, any ISN received from an application program for such a file is interpreted as an Adabas Vista ISN.
At the time the partition is defined, the space for a partition
identifier is reserved within the 4-byte ISN field. The size of this area is
based on the Adabas Vista file parameter
Maximum Number of
Partitions.
For example, the format of an Adabas Vista ISN for a standard
partitioned file defined with a Maximum Number of
Partitions set to 255 is as follows:
| Offset | Length | Contents | Meaning |
|---|---|---|---|
| 00 | 1 | X'01' - X'FF' | The ID of the partition from which the record was retrieved. |
| 01 | 3 | X'000000' - X'FFFFFF' | The Adabas ISN of the record within the physical partition |
Application programs that manipulate ISNs must be capable of handling the full 4-byte binary value returned. For Natural applications, any variable assigned to an ISN value should be defined with a minimum of P10. A value lower than this reduces the number of usable partitions and may result in a NAT1305 error code.
Caution:
Special care is required when an application uses an ISN value as
data. If a partitioned file is re-partitioned, the stored ISN may well become
inaccurate.
Caution:
When converting an Adabas file to a partitioned file, any ISNs for
the file that may have been stored as data in other files must go through a
conversion process to change the ISN values stored into correct Adabas Vista
ISN values.
Note:
Adabas Vista partitioned files may be defined as
"extreme", supporting > 4 gig ISNs. See
Using extreme files for more
information.
If an E1 command is issued with an ISN value
of zero and with a blank Command ID, the file is refreshed. This is also true
for a partitioned file.
Note:
The E1 command will be issued to each
partition in turn. Any error which occurs when a later partition is refreshed
(for example, Adabas response code 114 because the partition was not loaded
with PGMREFRESH=YES specified) will result in a
partially refreshed partitioned file.
The S5 command is not supported for
Partitioned Files.
When using Adabas Vista, it is recommended to use the GET
(L4) command to hold records immediately before modifying them.
This is particularly relevant to those programs that would otherwise use the
READ (L6) and FIND (S4)
commands against a partitioned file.
Refer also to the section Distributed Lock Mode.
When issuing an L9 command sequence, a
second direction change is not allowed for distributed access.
When processing a direction change during an
L9 command sequence, Adabas Vista places
restrictions on format and length overrides in the search buffer.
A RC command which uses the C, L or O
command options in order to release specific or all global format IDs will only
be issued to the database specified in the command. In addition, the command
options will always be changed to C to ensure that all global format IDs
generated by Adabas Vista are also released by Adabas.
Any program that accesses a partitioned file and requires the use of
ISN positioning (for example, a starting ISN on an
initialL3 command, or a minimum ISN value on an
initial Sx command) must ensure that the supplied ISN is in Adabas Vista
format. Adabas Vista then targets the appropriate partitions of the partitioned
file.
Adabas Vista does not support a Command ID value enclosed in parentheses as a search expression for partitioned file access.
The following Adabas ADARUN parameters may need to be tuned for use with Adabas Vista.
| Adabas Parameter | Description |
|---|---|
| LI |
If a single file is partitioned into n files within the same database, it may obtain as many as n TBI elements per user as required for Adabas Vista distributed access. The increase in TBI elements depends on the amount of this
distributed access and the number of partitions used in the average request.
Therefore, the value of the |
| LQ |
The |
| LU |
The |
| NAB |
The |
| NC |
If one or more partitions are added to a database for the first
time, the value for the |
| NH |
See the |
| NISNHQ |
Along with the
|
| NQCID |
Similar to the |
| NU |
If one or more partitions are added to a database for the first
time, the |
| PREFETCH |
This parameter is needed to control the Adabas Vista read-ahead feature at the job level. No other Adabas prefetch parameter is necessary. |
| TNAA, TNAE, TNAX, TT |
Where partitions span more than one database, it is possible that a user may, during a series of related accesses, request numerous consecutive records from the same database within a distributed access. This may result in Adabas timing the user out on the other databases involved in the distributed access, which produces a response code 9 when Adabas Vista tries to continue the sequence on these databases. The values for the parameters
|
When using Adabas Vista partitioned files, Adabas passwords and cipher codes must be the same for each partition.
Software AG strongly recommends that the use of ETID is consistent (identical) across all databases used for a client session.
 |
Warning: It is possible to dynamically change Vista translation rules (etc.) in the configuration file and apply the changes to a running system. Vista accommodates this as best as possible in running applications. For example, all active cursors (read loops, find loops, etc.) and active transactions must be allowed to complete using the former set of rules (on a per session basis) before dynamic switchover to the new rules takes place. This covers most but not all situations. For example, there can be implications for handling ET data if rule changes alter the location where ET data are stored; unpredictable results are possible - especially if the rarely used situation of using ET data without setting ETID is used by the application. However, altering the location of the ET data store using only standard Adabas (without Vista) is very problematic since applications need to be fully coordinated to all look to the new location (only after all ET data has been moved), otherwise unpredictable results can occur, this is no different when Vista is used. |
Adabas Vista generates transaction directives in accordance with
standard distributed transactions making it compliant with the use of Adabas
Transaction Manager. Correct distributed transaction processing is enforced by
Adabas Vista (that is, an application is expected to be well-formed in the way
it pursues transaction outcome). To explain...where multiple databases are
modified the application is expected to pursue transaction outcome to all the
changed databases, in series. For example, if two databases are modified then
Adabas Vista expects to see two ET commands (one to
each database) to cause a positive transaction outcome; or two
BT commands (one to each database) for a negative
transaction outcome. If an application tries to issue a transactional command
without having fully issued all ET/BT commands for
all databases in the previous transaction then RSP249 sub-code 496 will be
issued. This behavior is compliant with distributed transaction processing
standards, as implemented by Adabas Transaction Manager.
The runtime control
ET
Data Database Number is used to specify the location for
transaction data.
The P and M command options allow a program to commit
(ET) or back out (BT) a
transaction while leaving some records in hold status. Adabas Vista supports
these options using the Extended Hold runtime control.
Extended hold processing proceeds as follows:
Extended Hold = Minimum (default)
When Adabas Vista receives the first transaction directive, it has no knowledge of any P or M options that are to be applied to the databases involved in the transaction except those specified on this first directive.
Adabas Vista therefore honors the P or M option specified for the source database number of the first directive. It then generates the necessary directives for all other source database numbers without regard to P or M options. Thus, the client’s transaction is committed or rolled back as requested, P or M options on the first directive honored and all other ISNs released off hold.
Extended Hold = Maximum
When Adabas Vista receives the first transaction directive, it has no knowledge of any P or M options that are to be applied to the databases involved in the transaction except those specified on this first directive.
Adabas Vista therefore honors the P or M option specified for the source database number of the first directive, but ensures that held records put on hold using other source databases are not released during the commit or roll-back process. Thus, the client’s transaction is committed or rolled back as requested, but at this stage some of the transaction’s held records may still be in hold status.
As each subsequent directive (in the sequence) is issued, Adabas Vista honours the P or M option specified for those source database numbers. When the Vista proxy detects “end of directive sequence”, the proxy generates the necessary directives for each source database number that was not party to the client’s directive sequence.
If the application program fails to terminate the sequence of directives, records may unintentionally remain in hold status in one or more target databases. In this case, it is necessary to intervene manually by operator command or Adabas Online System to stop the client and free its resources; otherwise, the resources are freed when the client’s session times out.
Translation and partitioning features mean that CID commands may be re-directed to other databases/files which can cause inadvertent clashing of CIDs inside Adabas databases. Consequently the CID handling in Adabas Vista has now been strengthened to avoid this happening.
If an ET or CL
command with ET data is issued by a client and, as a result of this, Vista has
to generate a series of such commands, then Vista will always issue the ET data
on the first ET or CL of
the series. This is in accordance with standard distributed transaction
protocols making it compliant with the use of Adabas Transaction Manager.
The runtime control Database Number for ET Data is used to specify the location for transaction data.
|
Warning: It is possible to dynamically change Vista translation rules (etc.) in the configuration file and apply the changes to a running system. Vista accommodates this as best as possible in running applications. For example, all active cursors (read loops, find loops, etc.) and active transactions must be allowed to complete using the former set of rules (on a per session basis) before dynamic switchover to the new rules takes place. This covers most but not all situations. For example, there can be implications for handling ET data if rule changes alter the location where ET data are stored; unpredictable results are possible - especially if the rarely used situation of using ET data without setting ETID is used by the application. However, altering the location of the ET data store using only standard Adabas (without Vista) is very problematic since applications need to be fully coordinated to all look to the new location (only after all ET data has been moved), otherwise unpredictable results can occur, this is no different when Vista is used. |
Adabas Vista does not support the use of collation descriptors for partitioned files.
Changing the direction of an L3 or
L9 sequence when the sequence has been previously
subjected to multifetch is not allowed against a Partitioned File. This is
consistent with the behaviour of ADARUN PREFETCH (refer
to RSP021 sub-code 9 in the Adabas Messages and Codes
documentation).
