UKOUG Tech 2014

Monday, July 06, 2009

Dynamically Switching PeopleSoft Temporary Records between Global Temporary and Normal Tables during Application Engine Programs

I am working on a Time & Labour system. We run the main T&L process in different modes. There is a company wide overnight batch process, but individual parts of the company can run the process for their section during the day to process exceptions and to generate schedules. This is done with a custom AE program that calls the delivered TL_TIMEADMIN.

Running on Oracle 10gR2, we have faced performance problems caused by contention between concurrent truncate operations in these processes (see Factors Affecting Performance of Concurrent Truncate of Working Storage Tables).

One way to evade this problem is to convert the working storage tables to be Global Temporary Tables (GTTs). The contention problem caused by serialisation of truncate operations does not occur with GTTs. Last year I wrote a blog entry (Global Temporary Tables and PeopleSoft Temporary Records) that discussed when it was possible to use GTTs in Application Engine (AE) programs. Essentially, you can only use GTTs when restart is disabled for all AE programs that reference a temporary records.

So we could consider running the small but frequent daytime processes with restart disabled. Then we can make the non-shared instances of the temporary records into Global Temporary tables for the non-restartable daytime processes. However, we want to continue to run the overnight processes with restart enabled so that we have the option to restart a process that fails overnight from where it crashed, rather than going back to the beginning. The same non-shared instances may need to be Global Temporary during the day but normal recoverable tables by night.

Previously, I have only converted tables to Global Temporary where they are not referenced by a restartable AE program. I have now devised a way of switching a table to being a GTT if it is allocated to a process for which restart is disabled, and switching it back to a normal table if not. This is the best of both worlds.

When a non-shared instance of a temporary record is allocated to a particular process instance, a row is inserted into PS_AETEMPTBLMGR. The value of the restart disable flag is also stored in PS_AETEMPTBLMGR. I have created a trigger that switches a non-shared instance of a temporary record from a normal table to a GTT if restart is disabled, or switches it back to a normal table if restart is enabled. The trigger will create the GTT and any indexes on it if necessary, and will rename the tables as necessary so that the correct version has the default name expected by the process.

So if, for example, I have instance number 11 of a record called WRK_SHIFT_TAO, then the table will be called PS_WRK_SHIFT_TAO11. If that is allocated to a non-restartable AE program, the trigger will check for a table called GT_WRK_SHIFT_TAO11. If it doesn't exist the trigger will create it, dynamically generating the DDL with the dbms_metadata package. Thus, the structure of the GTT will be identical to PS_WRK_SHIFT_TAO11, the leading PS will also be changed to GT. The same indexes will also be created. The original normal table PS_WRK_SHIFT_TAO11 will be renamed to XX_WRK_SHIFT_TAO11, and then the GTT, at that point called GT_WRK_SHIFT_TAO11 will be renamed to PS_WRK_SHIFT_TAO11. The indexes are not renamed. If later the same instance is allocated to a restartable process, the change will be reversed by renaming again. The GTT will not be dropped so that it does not need to be recreated again the next time the non-restartable program uses it.

All DDL generated and executed by the trigger is written to the Message Log for that process (click on the screen shot to enlarge).

The shared instance of a record (the one without a instance number suffix) is never rebuilt as a Global Temporary table because it is possible that a restartable and non-restartable process might both use the shared instance at the same time.

One complication is how to handle changes to the temporary records. Application Designer will only create normal tables. So, if the table is to be rebuilt, them it needs to be switched back to a normal table, and the corresponding GTT created by the trigger should then be dropped. The Application Designer can recreate the table in the usual way. Next time the non-restartable AE runs, it will recreate the GTT with the new structure.

An updated version of T_LOCK is available which handles PeopleSoft temporary records and prevent DDL on PS_ tables with corresponding GT_ tables. The commands which swap these tables back and forth are explicitly permitted by the new version of this trigger.

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