Re: Consecutive Query Executions with Increasing Execution Time

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От Jeff Janes
Тема Re: Consecutive Query Executions with Increasing Execution Time
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Msg-id CAMkU=1w2i=Ph7840GYtf2eWta858Y3Eyb0zRKJd84cyEEctBZg@mail.gmail.com
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Ответ на Re: Consecutive Query Executions with Increasing Execution Time  (Laurenz Albe <laurenz.albe@cybertec.at>)
Ответы Re: Consecutive Query Executions with Increasing Execution Time  (Laurenz Albe <laurenz.albe@cybertec.at>)
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On Tue, Dec 17, 2019 at 8:08 AM Laurenz Albe <laurenz.albe@cybertec.at> wrote:
On Mon, 2019-12-16 at 15:50 -0500, Tom Lane wrote:
> Peter Geoghegan <pg@bowt.ie> writes:
> > Why do the first and the twentieth executions of the query have almost
> > identical "buffers shared/read" numbers? That seems odd.
>
> It's repeat execution of the same query, so that doesn't seem odd to me.

Really?  Shouldn't the blocks be in shared buffers after a couple
of executions?

If it is doing a seq scan (I don't know if it is) they intentionally use a small ring buffer to, so they evict their own recently used blocks, rather than evicting other people's blocks.  So these blocks won't build up in shared_buffers very rapidly just on the basis of repeated seq scans.
 
Cheers,

Jeff

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