In article <[EMAIL PROTECTED]>,
Scott Kirkwood <[EMAIL PROTECTED]> writes:

> I couldn't find anything in the docs or in the mailing list on this,
> but it is something that Oracle appears to do as does MySQL.
> The idea, I believe, is to do a quick (hash) string lookup of the
> query and if it's exactly the same as another query that has been done
> recently to re-use the old parse tree.

That's not was MySQL is doing.  MySQL caches not the query plan, but
the result set for the (hashed) query string.  If the same query comes
again, it is not executed at all (unless one of the tables involved
have been changed meanwhile).

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TIP 9: the planner will ignore your desire to choose an index scan if your
      joining column's datatypes do not match

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