Re: Set enable_seqscan doesn't take effect?

From: "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>
To: jacktby jacktby <jacktby(at)gmail(dot)com>
Cc: "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Set enable_seqscan doesn't take effect?
Date: 2023-09-28 04:26:06
Message-ID: CAKFQuwZhY1wA65gjDf10VK5SzzYe2+c_RV1SEEs_-ippuThBZg@mail.gmail.com
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On Wednesday, September 27, 2023, jacktby jacktby <jacktby(at)gmail(dot)com> wrote:

> postgres=# SET enable_seqscan = off;
> SET
> postgres=# explain select * from t;
> QUERY PLAN
> -------------------------------------------------------------------------
> Seq Scan on t (cost=10000000000.00..10000000023.60 rows=1360 width=32)

It wouldn’t cost 10billion to return the first tuple if that setting wasn’t
working.

That is the “discouragement” the documentation is referring to.

I do agree the wording in the docs could be improved since it is a bit
self-contradictory and unspecific, but it is explicitly clear a plan with
sequential scan can still be chosen even with this set to off.

David J.

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