| From: | Mark Kirkwood <markir(at)paradise(dot)net(dot)nz> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com>, Markus Schaber <schabi(at)logix-tt(dot)com>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: merge>hash>loop |
| Date: | 2006-04-19 05:33:02 |
| Message-ID: | 4445CB8E.5020800@paradise.net.nz |
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| Lists: | pgsql-performance |
Tom Lane wrote:
> Mark Kirkwood <markir(at)paradise(dot)net(dot)nz> writes:
>> Jim C. Nasby wrote:
>>> Good point. :/ I'm guessing there's no easy way to see how many blocks
>>> for a given relation are in shared memory, either...
>
>> contrib/pg_buffercache will tell you this -
>
> I think the key word in Jim's comment was "easy", ie, cheap. Grovelling
> through many thousands of buffers to count the matches to a given
> relation doesn't sound appetizing, especially not if it gets done over
> again several times during each query-planning cycle. Trying to keep
> centralized counts somewhere would be even worse (because of locking/
> contention issues).
>
Yeah - not sensible for a transaction oriented system - might be ok for
DSS tho.
Cheers
mark
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