| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Steve Wampler <swampler(at)noao(dot)edu> |
| Cc: | pgsql-sql(at)postgresql(dot)org |
| Subject: | Re: Make COUNT(*) Faster? |
| Date: | 2005-07-08 16:12:23 |
| Message-ID: | 23283.1120839143@sss.pgh.pa.us |
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| Lists: | pgsql-sql |
Steve Wampler <swampler(at)noao(dot)edu> writes:
> Tom Lane wrote:
>> If you want something cheap, you could use the same technique the
>> planner uses nowadays: take RelationGetNumberOfBlocks() (which is
>> guaranteed accurate) and multiply by reltuples/relpages.
> Yes - this would be an excellent approximation for my needs! The
> solution that Dawid Kuroczko suggested (just call "explain select *
> on ..." and parse the result) would be equivalent these days, right?
Close enough (the planner actually does some additional heuristic
stuff to avoid going crazy on corner cases).
regards, tom lane
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