Horton

Re: ATTACH/DETACH PARTITION CONCURRENTLY

Amit Langote <langote_amit_f8@lab.ntt.co.jp>

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From: Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>
To: Robert Haas <robertmhaas@gmail.com>, David Rowley <david.rowley@2ndquadrant.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>, Andres Freund <andres@anarazel.de>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Simon Riggs <simon@2ndquadrant.com>
Date: 2018-11-15T02:03:07Z
Lists: pgsql-hackers

Attachments

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

Commits

  1. Allow ATTACH PARTITION with only ShareUpdateExclusiveLock.

  2. Change lock acquisition order in expand_inherited_rtentry.

  3. Move code for managing PartitionDescs into a new file, partdesc.c

  4. Remove more redundant relation locking during executor startup.

  5. Add assertions that we hold some relevant lock during relation open.

  6. Try to acquire relation locks in RangeVarGetRelid.