|
You can use the ACT command to activate online extensibility for realms and DBTTs.
Activating online DBTT extensibility for a record type (ACT DBTT-INCR)
dbname
Name of the database comprising the record type or types for which online DBTT extension is to be activated. The database and the corresponding realm must already be attached at the time the DAL command is issued.
recordref
Number of the user record type for which online DBTT extension is to be activated. If it is to be activated for all record types then this specification can be omitted.
You can display the recordrefs of the record types using the DAL command DISPLAY DBTT-INCR or take them from the BPSIA log.
recordref=1 is used internally by UDS/SQL and cannot be specified here.
extnmbr
Minimum number of entries by which the DBTT is to be extended.
This specification must be greater than or equal to 1 and less than or equal to 99999999.
The default value is the number of DBTT entries in one DBTT extension.
You can display the current value of EXT parameter using the DAL command DIS-PLAY DBTT-INCR or take it from the BSTATUS output.
As a rule the actual number of DBTT entries by which the database is extended is somewhat greater than the desired number. The actual number depends on the following factors:
Page size of the database (2K, 4K or 8K)
DBTT line length of the record type concerned
If bottlenecks occur in the DBTT extension, the number of entries by which the DBTT is extended can also be less than the desired number. In all cases the number of DBTT entries by which the DBTT was actually extended will be displayed with a corresponding message.
SCAN=YES
In the event of a STORE, the online DBTT extension is only performed if no further free entries can be found in the entire DBTT - unless, that is, this transaction knows from other sources that all the DBTT entries are occupied. SCAN=YES is the default setting and thus corresponds to the behavior in the case of online DBTT extensibility not being activated, where in the event of a STORE the DBTT is run through completely again before "DBTT full" is reported.
This setting may result in this particular transaction inducing a long response time and blocking other transactions.
SCAN=NO
The online DBTT extension is performed as soon as the end of the DBTT is reached on a search for free entries; existing DBTT are only ever scanned once if this setting is active. This setting is of value for record types in which records are never or only very rarely deleted or for which any gaps in the DBTT due to deletions can be tolerated.
The ACT DBTT-INCR command schedules a request for the activation of an online DBTT extension for one or more record types or cancels a preceding DEACT DBTT-INCR request.
The request is not executed until the PERFORM command is issued. The message UDS0722 informs you of request execution as follows:
If an activation request has been executed for all record types then a single message is output for the database.
If an activation request has been executed for a single record type then a record typespecific message is output.
If activation requests have been executed for individual record types as well as for all record types then a single message is output for the database.
If multiple ACT DBTT-INCR requests are issued for one and the same record type then the specifications in the last issued request apply.
A DEACT DBTT-INCR request cancels a preceding ACT DBTT-INCR request for a record type and vice versa. This allows you to undo incorrectly issued ACT DBTT-INCR or DEACT DBTT-INCR requests before they are made effective with PERFORM.
The online extension of a record type remains activated until it is deactivated with DEACT DBTT-INCR.
If an online DBTT extension fails because of a suspended realm extension then a maximum of one message per record type is output to inform you that the online DBTT extension has failed. Any other messages relating to failed online DBTT extensions are suppressed until this suspension of the online realm extension has terminated.
If, on the activation of an online DBTT extension without a recordref specification i.e. activation for all the record types in a database, a realm with DBTTs is not attached, then the activation is not carried out for the corresponding record types. The message UDS0745 informs you of the realm in question.
If, on the activation of an online DBTT extension without a recordref specification i.e. activation for all the record types in a database, online realm extension is not activated for a realm with DBTTs or an online realm deactivation request is already present, then the activation is not carried out for the corresponding record types. The message UDS0744 informs you of the realm in question.
The ACT DBTT-INCR command is immediately rejected with message UDS0209 if
the specified record type number does not exist.
the specified database is not attached or is attached in
SHARED-RETRIEVAL mode.the corresponding DBTT realm is not attached for a specified record type. The message UDS0745 informs you of the realm in question.
online realm extension is not active for a specified record type or if there is already a request for the deactivation of the online realm extension of the DBTT realm. The message UDS0744 informs you of the realm in question.
an activation request for online DBTT for all record types in a database does not result in activation or the cancellation of a contrary request for any record type.
Activating online extensibility for a realm (ACT INCR)
dbname
Name of the database of the realm or realms for which online extensibility is to be activated.
dbname must be active when the command is issued.
dbname must not be in SHARED-RETRIEVAL mode.
realmref
Number of the realm for which online extensibility is to be activated. The realm must be active when the command is executed. The numbers of the activated realms can be displayed with DISPLAY INCR.
The numbers of all user realms and of the DBDIR are permitted. It is not permissible to specify the number of the DBCOM.
If RR=realmref is not specified, the command is executed with the same values for all user realms which have just been activated and for the DBDIR of the database dbname.
nr-pages
Number of database pages to be appended to the realm during online realm extension.
nr-pages=64 ... 16777215
The default value is 64.
nr-pages is increased by a maximum of 64 by the DBH during online realm extension, if space for a new FPA extent has to be deducted from the extension space.
Irrespective of nr-pages, an online realm extension is limited to the maximum number of possible database pages in the realm.
nr-pages does not relate to the number of pages by which the realm is extended by the DMS, but to the number of database pages.
In the case of realms that only contain DBTTs and are therefore only activated for online DBTT extension, it is not necessary to specify nr-pages since UDS/SQL extends the realm on the basis of internal rules.
min-pages
Limit value for free database pages in realm.
min-pages=0 ... nr-pages
The default value is 16.
min-pages has the following effect:
min-pages=0
Realm extension is started if a free space search has been unsuccessful.
min-pages>0
If the number of currently existing free database pages falls below min-pages, then a free space search will result in a realm expansion.
Realm extension will be performed, even if it is not yet necessary for carrying out the current request. This enables further transactions requiring free place in the realm to be performed during online realm extension.
In the case of realms that only contain DBTTs and are therefore only activated for online DBTT extension, it is not necessary to specify min-pages since UDS/SQL extends the realm on the basis of internal rules.
The command ACT INCR will note a request to activate online extensibility, for the realm realmref in the database dbname. If RR=realmref is not specified, the request will be noted to activate online extensibility for all activated realms in the database dbname.
ACT INCR can also undo a previously issued DEACT INCR command, provided the commands have not already been executed with PERFORM. ACT INCR will only ever be executed once PERFORM has been specified. If you have issued several ACT INCR requests for a single realm, the data of the last request applies.
DAL requests pending in addition to ACT INCR may also contain requests which will drop the realms or databases affected. In this case, it does not matter if the DROP requests are entered before or after the ACT INCR requests. When PERFORM is issued, ACT INCR requests for a database are always processed first.
If online extensibility was suspended for the specified realm(s), ACT INCR will cancel the suspension, i.e. ACT INCR includes the function of the REACT INCR command.
The online expandability of a realm remains activated until it is deactivated by the command DEACT INCR.
If online realm extension is active then the termination of suspension may result in messages reporting the failure of DBTT extensions in this realm if a renewed suspension occurs.
The command ACT INCR is rejected immediately, if:
an invalid value was specified for nr-pages or min-pages.
the database dbname has not been activated, or has been activated in SHARED-RETRIEVAL mode.
the specified realm number realmref does not exist.
the DBCOM realm number was specified as the realm number realmref.
the specified realm has not been activated.