Re: Is the unfair lwlock behavior intended?

On 2016-05-25 11:15:37 -0700, Andres Freund wrote:
> On 2016-05-25 14:09:43 -0400, Robert Haas wrote:
> I don't think anybody was doing that? The first questions on this thread
> were about upgrading and retesting...

Something I've repeatedly wondered about around this topic is whether we
could split ProcArrayLock into one that governs entering or leaving the
procarray from the one that's for consistent snapshots.  I think there's
no need for ProcArrayAdd/ProcArrayRemove/CountDBBackends()/CancelDBBackends()/
CountUserBackends()/CountOtherDBBackends() (and potentially some more)
to conflict with GetSnapshotData()/ProcArrayEndTransaction()/
TransactionIdIsInProgress()/TransactionIdIsActive()/GetOldestXmin()/...
as long as we're careful to ensure that by the time a entry is removed
ProcArrayEndTransaction() has been called.

Greetings,

Andres Freund