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Re: [HACKERS] too low cost of Bitmap index scan - Mailing list pgsql-hackers

From Tom Lane
Subject Re: [HACKERS] too low cost of Bitmap index scan
Date
Msg-id 6271.1482274893@sss.pgh.pa.us
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In response to [HACKERS] too low cost of Bitmap index scan  (Pavel Stehule <pavel.stehule@gmail.com>)
Responses Re: [HACKERS] too low cost of Bitmap index scan  (Pavel Stehule <pavel.stehule@gmail.com>)
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Pavel Stehule <pavel.stehule@gmail.com> writes:
> I am trying to fix slow query on PostgreSQL 9.5.4.
> The data are almost in RAM

If it's all in RAM, you'd likely be well-served to lower random_page_cost.
It looks to me like the planner is estimating pretty accurately how many
heap fetches will be eliminated by using the extra index; where it's off
seems to be in the cost of those heap fetches relative to the index work.
        regards, tom lane

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