From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Amit Langote <amitlangote09@gmail.com>
Cc: Justin Pryzby <pryzby@telsasoft.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: ALTER TABLE .. DETACH PARTITION CONCURRENTLY
Date: Tue, 27 Apr 2021 11:47:33 -0400
Message-ID: <20210427154733.GA28178@alvherre.pgsql> (raw)
In-Reply-To: <CA+HiwqGTjrgbA7EbgUvzbc2VuS5ijmWHMw+pQE4U1riMpT9Yww@mail.gmail.com>
On 2021-Apr-27, Amit Langote wrote:
> On Tue, Apr 27, 2021 at 4:34 PM Amit Langote <amitlangote09@gmail.com> wrote:
> I think we may need a separate context for partdesc_nodetached, likely
> with the same kludges as rd_pdcxt. Maybe the first problem will go
> away with that as well.
Ooh, seems I completely misunderstood what RelationClose was doing. I
thought it was deleting the whole rd_pdcxt, *including* the "current"
partdesc. But that's not at all what it does: it only deletes the
*children* memcontexts, so the partdesc that is currently valid remains
valid. I agree that your proposed fix appears to be promising, in that
a separate "context tree" rd_pddcxt (?) can be used for this. I'll try
it out now.
> Few other minor things I noticed:
>
> + * Store it into relcache. For snapshots built excluding detached
> + * partitions, which we save separately, we also record the
> + * pg_inherits.xmin of the detached partition that was omitted; this
> + * informs a future potential user of such a cached snapshot.
>
> The "snapshot" in the 1st and the last sentence should be "partdesc"?
Doh, yeah.
> + * We keep two partdescs in relcache: rd_partdesc_nodetached excludes
> + * partitions marked concurrently being detached, while rd_partdesc includes
> + * them.
>
> IMHO, describing rd_partdesc first in the sentence would be better.
> Like: rd_partdesc includes all partitions including any that are being
> concurrently detached, while rd_partdesc_nodetached excludes them.
Makes sense.
--
Álvaro Herrera Valdivia, Chile
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Cc: alvherre@alvh.no-ip.org, amitlangote09@gmail.com, pryzby@telsasoft.com, tgl@sss.pgh.pa.us, pgsql-hackers@lists.postgresql.org
Subject: Re: ALTER TABLE .. DETACH PARTITION CONCURRENTLY
In-Reply-To: <20210427154733.GA28178@alvherre.pgsql>
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