The SESAM/SQL DBH analyzes the statements in the application program to check that they are lexically, syntactically and semantically correct. The DBH takes a correct statement or a subarea of an SQL statement and generates an optimized format known as the internal statement format from it.
Based on a CALL DML statement, the DBH generates the internal statement format directly.
With an SQL statement, the DBH initially generates an SQL access plan, in other words a statement rule for the SQL statement. An SQL access plan consists of at least one but usually several subareas known as SQL scans. The optimized format of a scan is what finally constitutes the internal statement format.
Internal statement formats are placed in the work container so that they can be accessed by follow-up statements. A follow-up statement can, for instance, be the SQL statement FETCH or continuation of processing after a previously locked transaction has been unlocked.
This approach considerably reduces the amount of effort that has to be invested in analysis and optimization.
Using a DBH option, system administrators can specify a suitable size for the work container when the DBH session is started. 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. 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).