When SQL access plans are processed, SQL scans are produced. These are subareas of an evaluation rule for an SQL statement.
During the processing of CALL DML applications, inquiry and response areas are requested for each logical file with the OPEN statement.
In order to have main memory available for the inquiry and response areas of SQL scans or logical files, the SESAM/SQL DBH maintains the transfer container, which is administered in fixed units of 256 bytes each.
Transfer container size
At the beginning of the DBH session, the DBH creates a transfer container of a specific size. The basic transfer container size is 64Kbytes, but this can be increased using a DBH option. Frequent requests for storage during a session can cause the transfer container to be become seriously fragmented, with the result that the DBH can ultimately no longer complete the current requests. When this occurs, the transfer container is reorganized. If this does not produce the desired effect, the DBH increases the size of the transfer container up to a given maximum.
Using a DBH option, system administrators can specify a suitable size for the basic and the maximum container size setting. During DBH operation they can use the administration statement MODIFY-STORAGE-SIZE to modify the maximum size to suit the requirements of the current session. In this context, useful information is provided in the DBH statistics supplied by the SESAM/SQL utility SESMON in its “SYSTEM INFORMATION” screen (see the “Database Operation” manual).