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Profiling Execution Plans

In my previous blog post, I demonstrated how to identify the active lines in an adaptive execution plan on DBA_HIST_SQL_PLAN so that I could profile behaviour. This post demonstrates a practical application of that technique. This statement comes out of the PeopleSoft Financials Multi-currency Processing. A process extracts groups of rows in elimination sets into a working storage table and joins that table to the ledger table for further processing. The number of rows extracted from the elimination set selector table (PS_ELIM_CF_SEL2001 in this case) can vary in a single process from a few to a few thousand. However, the process does regather optimizer statistics each time.

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Hints, Patches, Force Matching and SQL Profiles

Sometimes, when all else fails, it is necessary to add hints to a piece of SQL in order to make the optimizer use a particular execution plan. We might directly add the hint to the code. However, even if it is possible to access the code directly, that may not be a good idea. In the future, if we need to change the hint, possibly due to a change in optimizer behaviour on database upgrade, then we would again need to make a code change.
Instead, we could look at Oracle's plan stability technologies.  There are 4 plan stability features in the database. They are different, but conceptually they all involve associating a set of hints with a statement that will be picked up by the optimizer at runtime.

Diagnosing Non-Intuitive Errors with Errorstack

This is a story about how to diagnose a problem where the error message did not seem to make sense, nor have any apparent relation to what I thought was happening.

The Problem 

During a PeopleSoft on Exadata Proof-of-concept test, running on Oracle, we got this error in a COBOL process in PeopleSoft North American Payroll.

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Action Type : SQL SELECT
With Return Code: 31011
Error Message : ORA-31011: XML parsing failed ORA-19202: Error occurred in XML processing LPX-00210: expected '<' instead of '�' Error at line 1

OOW14 Session: SQL Tuning Without Trying

Many thanks to all those who attended my session "SQL Tuning without Trying" at Oracle Open World 2014 #oow14. I hope you found the session useful.

If you want to download the slide deck, here it is. As always, I would really, really like to hear from you.