Horton

Re: BackendKeyData is mandatory?

David G. Johnston <david.g.johnston@gmail.com>

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From: "David G. Johnston" <david.g.johnston@gmail.com>
To: Tatsuo Ishii <ishii@postgresql.org>
Cc: "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2025-06-17T03:06:26Z
Lists: pgsql-hackers 
On Monday, June 16, 2025, Tatsuo Ishii <ishii@postgresql.org> wrote:

>
> My question is, BackendKeyData is mandatory or not. Currently
> Pgpool-II raises a fatal error if BackendKeyData is not sent before
> ReadyForQuery arrives. This is because without the message, frontend
> cannot send a CancelRequest message later on, as there's no secret
> key.


I wouldn’t expect a proxy to make a judgement here; but to simply forward
what does show up and otherwise stay silent.  If there is proxy layer code
needed to deal with its absence ignoring the cancel attempt with a log
warning would be sufficient.  Otherwise, the user has made their choices
and this is an optional feature in practice (though resorting to
pg_cancel_query make be required for truly hung processes).

David J.

Commits

  1. Revert unnecessary check for NULL

  2. libpq: Be strict about cancel key lengths

  3. libpq: Handle OOM by disconnecting instead of hanging or skipping msgs

  4. libpq: Complain about missing BackendKeyData later with PGgetCancel()