From: Tom Lane <tgl@sss.pgh.pa.us>
To: gzh <gzhcoder@126.com>
Cc: pgsql-general@lists.postgresql.org
Subject: Re: ERROR: stack depth limit exceeded
Date: Fri, 08 Sep 2023 09:53:33 -0400
Message-ID: <1871319.1694181213@sss.pgh.pa.us> (raw)
In-Reply-To: <1211c4ba.2822.18a72d975fc.Coremail.gzhcoder@126.com>
References: <1e6b9056.492e.18a6e9a1798.Coremail.gzhcoder@126.com>
<1694898.1694093396@sss.pgh.pa.us>
<1211c4ba.2822.18a72d975fc.Coremail.gzhcoder@126.com>
gzh <gzhcoder@126.com> writes:
> In the Release Notes for PostgreSQL 12.14, we saw the following change:
> https://www.postgresql.org/docs/release/12.14/>> Add recursion and looping defenses in subquery pullup (Tom Lane)
>> A contrived query can result in deep recursion and unreasonable amounts of time spent trying to flatten subqueries. A proper fix for that seems unduly invasive for a back-patch, but we can at least add stack depth checks and an interrupt check to allow the query to be cancelled.
> Our understanding is that this change will cause some complex SQL statements
> that were previously not reporting errors to report errors in the new version.
The key word there is "contrived". You are not going to hit this limit
without intentionally trying. The example that led to adding this check
was a synthetic query with 10000 UNION ALL branches:
https://www.postgresql.org/message-id/flat/703c09a2-08f3-d2ec-b33d-dbecd62428b8%40postgrespro.ru
Also notice that the query misbehaved before this patch, too, by consuming
excessive RAM.
regards, tom lane
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To: pgsql-general@postgresql.org
Cc: tgl@sss.pgh.pa.us, gzhcoder@126.com, pgsql-general@lists.postgresql.org
Subject: Re: ERROR: stack depth limit exceeded
In-Reply-To: <1871319.1694181213@sss.pgh.pa.us>
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