Re: ATTACH/DETACH PARTITION CONCURRENTLY

From: Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>
To: Robert Haas <robertmhaas(at)gmail(dot)com>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>
Cc: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Simon Riggs <simon(at)2ndquadrant(dot)com>
Subject: Re: ATTACH/DETACH PARTITION CONCURRENTLY
Date: 2018-11-15 02:03:07
Message-ID: bda29028-75ec-08c7-b874-0a9725fb19c6@lab.ntt.co.jp
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On 2018/11/15 4:27, Robert Haas wrote:
> RelationBuildPartitionDesc doesn't lock the children
> whose relpartbounds it is fetching (!), so unless we're guaranteed to
> have already locked them children earlier for some other reason, we
> could grab the partition bound at this point and then it could change
> again before we get a lock on them.

Hmm, I think that RelationBuildPartitionDesc doesn't need to lock a
partition before fetching its relpartbound, because the latter can't
change if the caller is holding a lock on the parent, which it must be if
we're in RelationBuildPartitionDesc for parent at all. Am I missing
something?

As Michael pointed out, the first cleanup patch needs to be rebased due to
a recent commit [1]. I did that to see if something we did in that commit
made things worse for your patch, but seems fine. I had to go and change
things outside RelationBuildPartitionDesc as I rebased, due to the
aforementioned commit, but they're simple changes such as changing List *
arguments of some newly added functions to PartitionBoundSpec **. Please
find the rebased patches attached with this email.

Thanks,
Amit

[1] https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=b52b7dc2

Attachment Content-Type Size
0001-Reduce-unnecessary-list-construction-in-RelationBuil.patch text/plain 11.7 KB
0002-Ensure-that-RelationBuildPartitionDesc-sees-a-consis.patch text/plain 6.1 KB

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