| From: | Christopher Kings-Lynne <chriskl(at)familyhealth(dot)com(dot)au> |
|---|---|
| To: | Michael Rothschild <michael(dot)r(at)corigin(dot)co(dot)il> |
| Cc: | pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: |
| Date: | 2003-12-25 02:47:28 |
| Message-ID: | 20031225104501.V58695-100000@houston.familyhealth.com.au |
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| Thread: | |
| Lists: | pgsql-performance |
> For example, if I have the following query:
> Select * from a where x in (select y from b where z=7)
> Then I would expect an index or hash structure to be created for b.y
> when it is first scanned and brought into the cache but I couldn't see
> it happening in the source.
> As I said, I only inferred it from reading the source - not from actual
> experiments - so I may be wrong.
> 1. Am I wrong?
You are wrong - this is old behaviour and one of the major speed
improvements of PostgreSQL 7.4 is that IN subqueries now use a hash index
and hence they are much faster.
Chris
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