Re: hot_standby_feedback vs excludeVacuum and snapshots

On 6 July 2018 at 03:30, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com> wrote:
> On Thu, Jul 5, 2018 at 8:27 AM, Noah Misch <noah(at)leadboat(dot)com> wrote:
>>> However, 49bff5300d527 also introduced a similar bug where subtransaction
>>> commit would fail to release an AccessExclusiveLock, leaving the lock to
>>> be removed sometimes early and sometimes late. This commit fixes
>>> that bug also. Backpatch to PG10 needed.
>>
>> Subtransaction commit is too early to release an arbitrary
>> AccessExclusiveLock. The primary releases every AccessExclusiveLock at
>> top-level transaction commit, top-level transaction abort, or subtransaction
>> abort. CommitSubTransaction() doesn't do that; it transfers locks to the
>> parent sub(xact). Standby nodes can't safely remove an arbitrary lock earlier
>> than the primary would.
>
> But we don't release locks acquired by committing subxacts until the
> top level xact commits. Perhaps that's what the git commit message
> meant by "early", as opposed to "late" meaning when
> StandbyReleaseOldLocks() next runs because an XLOG_RUNNING_XACTS
> record is replayed?

Locks held by subtransactions were not released at the correct timing
of top-level commit; they are now.

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Simon Riggs http://www.2ndQuadrant.com/
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