Monday, 21 May 2007

On SQL_TRACE et al.

Back again for another day of site maintenance and blogging.

This time, I'm still on the SQL Tracing page, extending it and making it much better and easier to follow. I've extended the section on AUTOTRACE, expanding on a few things, and (thanks to Yasin Baskan for this) including something I'd forgotten, which is that setting AUTOTRACE ON (or any setting which generates statistics, this doesn't include SET AUTOTRACE TRACEONLY EXPLAIN, of course) generates an "extra" session which is used to maintain the statistics for the "main" session, i.e. the one you executed the query in, which, as Yasin rightly points out, can itself offer SQL performance challenges.

I've also expanded on the DBMS_XPLAN bit, putting in how to utilise a seperate plan table from

Hopefully, I'll get around to reviewing the Cardinality page later, that's another page that needs a little bit of attention.

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