Horton

Re: Condition variable live lock

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Thomas Munro <thomas.munro@enterprisedb.com>, Andres Freund <andres@anarazel.de>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2018-01-05T20:03:19Z
Lists: pgsql-hackers 
Robert Haas <robertmhaas@gmail.com> writes:
> On Fri, Jan 5, 2018 at 2:38 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> * I think the Asserts in ConditionVariablePrepareToSleep and
>> ConditionVariableSleep ought to be replaced by full-fledged test and
>> elog(ERROR), so that they are enforced even in non-assert builds.
>> I don't have a lot of confidence that corner cases that could violate
>> those usage restrictions would get caught during developer testing.
>> Nor do I see an argument that we can't afford the cycles to check.

> I think those usage restrictions are pretty basic, and I think this
> might be used in some places where performance does matter.  So -1
> from me for this change.

Really?  We're about to do a process sleep, and we can't afford a single
test and branch to make sure we're doing it sanely?

>> * A lot of the comments could be improved, IMHO.

> No opinion without seeing what you propose to change.

OK, will put out a proposal.

			regards, tom lane

Commits

  1. Add WL_EXIT_ON_PM_DEATH pseudo-event.

  2. While waiting for a condition variable, detect postmaster death.

  3. Fix race condition during replication origin drop.

  4. Allow ConditionVariable[PrepareTo]Sleep to auto-switch between CVs.

  5. Cosmetic improvements in condition_variable.[hc].

  6. Improve error detection capability in proclists.

  7. Remove return values of ConditionVariableSignal/Broadcast.

  8. Reorder steps in ConditionVariablePrepareToSleep for more safety.

  9. Rewrite ConditionVariableBroadcast() to avoid live-lock.

  10. Add parallel-aware hash joins.