Re: Query uses incorrect index

От: Kevin Grittner
Тема: Re: Query uses incorrect index
Дата: ,
Msg-id: 4D119B40020000250003892D@gw.wicourts.gov
(см: обсуждение, исходный текст)
Ответ на: Query uses incorrect index  (pasman pasmański)
Список: pgsql-performance

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Query uses incorrect index  (pasman pasmański, )
 Re: Query uses incorrect index  ("Kevin Grittner", )
 Re: Query uses incorrect index  (pasman pasmański, )
  Re: Query uses incorrect index  (Guillaume Cottenceau, )
  Re: Query uses incorrect index  (Tom Lane, )
 Re: Query uses incorrect index  ("Kevin Grittner", )
 Re: Query uses incorrect index  (pasman pasmański, )

Guillaume Cottenceau  wrote:

> If I'm correct, you're basically telling postgresql that your
> disk is unusually fast compared to your CPU. Even if some queries
> will run faster from a side-effect of these settings, you're
> likely to create other random problems...

If this is set globally and the active portion of the database is not
highly cached, yes.  If the example query is typical of the level of
caching for frequently-run queries, it might provide an overall
performance boost to set these in postgresql.conf.

The original problem was that the optimizer was grossly
over-estimating the cost of returning a tuple through the index,
which was taking about 0.01 ms per tuple.

-Kevin


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