Re: tds_fdw : Severe performance degradation from postgresql 10.23 to 16.4

From: Achilleas Mantzios - cloud <a(dot)mantzios(at)cloud(dot)gatewaynet(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Tomas Vondra <tomas(at)vondra(dot)me>, pgsql-performance(at)lists(dot)postgresql(dot)org, "P(dot)Groidis" <itdev(at)gatewaynet(dot)com>
Subject: Re: tds_fdw : Severe performance degradation from postgresql 10.23 to 16.4
Date: 2024-11-13 07:14:18
Message-ID: d31cd123-60e2-44e8-8fa4-409aac926c95@cloud.gatewaynet.com
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On 11/12/24 21:37, Tom Lane wrote:
> Achilleas Mantzios <a(dot)mantzios(at)cloud(dot)gatewaynet(dot)com> writes:
>> Our sysadm created the system debian Debian GNU/Linux 12 (bookworm)with
>> postgres as user 1000. Now at some point we realized that whenever we
>> run a pgsql cluster with another user (I found that after spending two
>> good days testing), the above query runs in about 1 second. With user
>> postgres 1000 in 30 seconds. As you saw the perf output are completely
>> different.
> Don't recall details offhand, but in some situations where the calling
> SQL user doesn't have permissions to read particular columns, the
> planner will not consult statistics for those columns. That can lead
> to a different, less optimal plan being used. Maybe something like
> that is happening here?

Thank you Tom,

In all runs of this query the user is postgres (superuser). Besides,
this is just a simple query run on a FOREIGN TABLE living in a MS SQL
Server.

>
> regards, tom lane

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