| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Kevin Hunter <hunteke(at)earlham(dot)edu> |
| Cc: | Tyler Durden <tylersticky(at)gmail(dot)com>, PostgreSQL General <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: Seq Scan |
| Date: | 2007-06-01 21:15:04 |
| Message-ID: | 23905.1180732504@sss.pgh.pa.us |
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| Lists: | pgsql-general |
Kevin Hunter <hunteke(at)earlham(dot)edu> writes:
> At 1:17p -0400 on 01 Jun 2007, Tyler Durden wrote:
>> I find strange that a simple SELECT COUNT(...) is so slow with only
>> 700 000 records.
> The much more knowledgable will correct me, but the abbr. version is
> that it is for data integrity and correctness reasons and the
> inherent way in which the MVCC model works.
The bottom line is that a "correct" implementation (ie, one that fully
respects MVCC behavior) would create enormous overhead, as well as bad
contention bottlenecks for concurrent updates. It doesn't seem worth it.
If you want a cheap approximate answer, there are a couple of ways to
get one, but SELECT COUNT(*) is not that.
regards, tom lane
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