From: | Andreas Pflug <Andreas(dot)Pflug(at)web(dot)de> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-performance(at)postgresql(dot)org |
Subject: | Re: [SQL] Yet Another (Simple) Case of Index not used |
Date: | 2003-04-20 15:37:57 |
Message-ID: | 3EA2BED5.9010707@web.de |
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Lists: | pgsql-general pgsql-performance pgsql-sql |
Tom Lane wrote:
>It would be counting the wrong thing. auto-vacuum needs to know how
>many dead tuples are in a table, not how many live ones. Example:
>UPDATE doesn't change the live-tuple count (without this property,
>I don't think the sort of count maintenance Kevin is proposing could
>possibly be efficient enough to be interesting). But it does create
>a dead tuple that vacuum wants to know about.
>
>
>
I understand your point, but is this about VACUUM only or VACUUM ANALYZE
too? People wouldn't bother about big databases if it's still fast
(until the disk is full :-)
Do dead tuples affect query planning? I thought the plan only cares
about existing rows and their data patterns.
So count(*), pg_stat_all_tables.n_tup_ins, .n_tup_upd and .n_tup_del all
together can make a VACUUM ANALYZE necessary, right?
Regards,
Andreas
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