| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> |
| Cc: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Peter Geoghegan <pg(at)bowt(dot)ie>, Shijia Wei <shijiawei(at)utexas(dot)edu>, Pgsql Performance <pgsql-performance(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Consecutive Query Executions with Increasing Execution Time |
| Date: | 2019-12-18 13:44:14 |
| Message-ID: | 28392.1576676654@sss.pgh.pa.us |
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| Lists: | pgsql-performance |
Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> writes:
> On Tue, 2019-12-17 at 11:11 -0500, Jeff Janes wrote:
>> 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.
> Sure, but according to the execution plans it is doing a Parallel Index Only Scan.
Nonetheless, the presented test case consists of repeatedly doing
the same query, in a fresh session each time. If there's not other
activity then this should reach some sort of steady state. The
table is apparently fairly large, so I don't find it surprising
that the steady state fails to be 100% cached.
regards, tom lane
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