Nigel Noble's Oracle Blog

11/01/2011

10.2.0.5 dbms_sql leaks memory AND performance degrades

Filed under: Uncategorized — Nigel Noble @ 11:24 am

My site recently upgraded one of its databases to the 10.2.0.5 patchset and found a serious performance problem relating to code using dbms_sql. Once we had completed the upgrade, we noticed a number of data feeds to the upgraded database started to fall behind and could no longer keep up. When we stopped and restarted the feeds they appeared to speed up. After some investigation we found two problems, the first relating to a “log file sync” problem in RAC which is still under investigation (one for a future post when we have more detail) but the second issue caused the performance of the data feed to degrade steadily over time.  

We use a couple of products to dynamically feed data to our 10.2.0.5 database and it seemed the performance degraded  over time (many days). We did a 10046 session trace and found we lost a lot of time between the dbms_sql.parse of some dynamic SQL and the bind phase. We found reference in Metalink to Bug 10269717 (DBMS_SQL.PARSE leaks session heap memory in 10.2.0.5).  Although the bug discusses a memory leak, we found that the performance also degrades over time.

We applied the patch for 10269717 and the PGA memory leak was resolved but more importantly the performance remained constant. I just checked the 10.2.0.5 known issues document and this does now list the bug, but it still only references the leak and not the performance implications.

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