| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | "Craig A(dot) James" <cjames(at)modgraph-usa(dot)com> |
| Cc: | pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: explain analyze reports 20x more time than actual |
| Date: | 2006-06-30 06:04:49 |
| Message-ID: | 20524.1151647489@sss.pgh.pa.us |
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| Lists: | pgsql-performance |
"Craig A. James" <cjames(at)modgraph-usa(dot)com> writes:
> I have a query that needs to run faster, with the obvious solution
> being to add an index. But to confirm this, I ran explain analyze.
> When I run the actual query, it consistently takes 6-7 seconds by the
> wall clock. My application with a "verbose" mode enabled reports 6.6
> seconds consistently. However, when I run EXPLAIN ANALYZE, it takes
> 120 seconds!
See recent discussions --- if you've got duff PC hardware, it seems that
reading the clock takes forever :-(. In this case I'd assume that the
cost of the seqscan (11497361 rows returned) is being overstated because
of the 2*11497361 gettimeofday calls involved.
regards, tom lane
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