Re: Query ID Calculation Fix for DISTINCT / ORDER BY and LIMIT / OFFSET

From: David Rowley <dgrowleyml(at)gmail(dot)com>
To: Michael Paquier <michael(at)paquier(dot)xyz>
Cc: Sami Imseih <samimseih(at)gmail(dot)com>, Ivan Bykov <I(dot)Bykov(at)modernsys(dot)ru>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Query ID Calculation Fix for DISTINCT / ORDER BY and LIMIT / OFFSET
Date: 2025-03-18 08:24:06
Message-ID: CAApHDvq0cD18xUFFnJ2tGGFFAMU-h=gXc=g2E4sqsYX7J3__EQ@mail.gmail.com
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On Tue, 18 Mar 2025 at 21:00, Michael Paquier <michael(at)paquier(dot)xyz> wrote:
> If we make the whole cheaper with only extra entropy added for NULLs
> in nodes and strings, I'd rather have an insurance policy for the
> custom functions. Something like that:
> - Forbid a size of 0 in AppendJumble().
> - When dealing with a non-NULL case in _jumbleNode(), save the initial
> jumble_len and the jumble contents when starting, then complain if the
> jumble_len matches with the initial length at the end and if the
> contents are the same in an assert. A check on the length may be
> enough, but we'd depend on JUMBLE_SIZE and nodes can get pretty big.
>
> What do you think?

If it's for Assert enabled builds only, then to save from having to
look at the buffer, you could have an extra field similar to
jumble_len, but does not get reset when the jumble buffer fills. Just
assert that the total_jumbled_bytes has grown after jumbling a node,
maybe?

David

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