The actual extension operation for a DBTT is initiated automatically by the DBH if a search for a free entry reveals that the last entry is occupied (SCAN=NO) or that there are no more free entries in the entire DBTT (SCAN=YES). The DBTT extension is performed within this DML’s user transaction. Although this increases the DML’s response time, the impairment to overall operation due to this process is small.
The period required for online DBTT extension is largely dependent on the time required for the associated online realm extension.
In the case of an online DBTT extension, the realm containing the DBTT is extended in all cases. This obligatory realm extension represents only a very small burden for ongoing transaction operation.
The realm is only extended by the necessary amount, not by the values specified on activation of online realm extension. This means that no superfluous empty pages are created as a result of an online realm extension for a DBTT.
If it was possible to extend the DBTT, the following message is output:
UDS0741 DBTT HAS BEEN EXTENDED: (&00) DBTT ENTRIES
The insert (&00) indicates the record name and the number of DBTT entries by which the DBTT was extended.
If a number of entries was specified in the EXT parameter, then the DBTT will be extended by a rounded up number of DBTT entries required for DBTT extension. The actual number of DBTT entries depends on the page size of the database and the DBTT line length of the record type concerned.