Horton

Re: Condition variable live lock

Thomas Munro <thomas.munro@enterprisedb.com>

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From: Thomas Munro <thomas.munro@enterprisedb.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2018-01-05T21:25:27Z
Lists: pgsql-hackers 
On Sat, Jan 6, 2018 at 6:33 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> As I feared, the existing regression tests are not really adequate for
> this: gcov testing shows that the sentinel-inserting code path is
> never entered, meaning ConditionVariableBroadcast never sees more
> than one waiter.  What's more, it's now also apparent that no outside
> caller of ConditionVariableSignal ever actually awakens anything.
> So I think it'd be a good idea to expand the regression tests if we
> can do so cheaply.  Anybody have ideas about that?  Perhaps a new
> module under src/test/modules would be the best way?  Alternatively,
> we could drop some of the optimization ideas.

I think I might have a suitable test module already.  I'll tidy it up
and propose it in a few days.

> BTW, at least on gaur, this does nothing for the runtime of the join
> test, meaning I'd still like to see some effort put into reducing that.

Will do.

-- 
Thomas Munro
http://www.enterprisedb.com

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.