Horton

Re: BUG #14830: Missed NOTIFications, PostgreSQL 9.1.24

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

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Marko Tiikkaja <marko@joh.to>, Michael Paquier <michael.paquier@gmail.com>, PostgreSQL mailing lists <pgsql-bugs@postgresql.org>
Date: 2017-10-10T18:07:36Z
Lists: pgsql-bugs

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I wrote:
> Wait, I have an idea.  Let's fetch a snapshot at the top of
> ProcessIncomingNotify, and then use the snapshot to decide whether
> xids are running, instead of calling TransactionIdIsInProgress.

Concretely, I suggest the attached patch.  I tried Marko's testbed
against this, and it seems indeed a bit faster than before ---
running it for 100000 notifies takes about 19.25 seconds, rather than
19.5 seconds with HEAD.  But the testbed is probably about the best
case because it has a bunch of threads sending notifies to one
receiver, so that the receiver is quite likely to have multiple
messages to read at a time.  OTOH, in a situation where the NOTIFY
traffic isn't so high, it probably hardly matters anyway.

			regards, tom lane

Commits

  1. Fix low-probability loss of NOTIFY messages due to XID wraparound.