From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Marko Tiikkaja <marko@joh.to>
Cc: Michael Paquier <michael.paquier@gmail.com>
Cc: PostgreSQL mailing lists <pgsql-bugs@postgresql.org>
Subject: Re: BUG #14830: Missed NOTIFications, PostgreSQL 9.1.24
Date: Tue, 10 Oct 2017 16:06:21 +0200
Message-ID: <20171010140621.u4avva4cxylwpyew@alvherre.pgsql> (raw)
In-Reply-To: <15645.1507643938@sss.pgh.pa.us>
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Tom Lane wrote:
> Marko Tiikkaja <marko@joh.to> writes:
> > So I managed to accidentally kill and/or restart both servers while trying
> > to install debug symbols, but I'm doing a new run now and I noticed
> > something interesting: the listening backend's RecentXmin doesn't seem to
> > ever go forward. By my reading of this code, that would mean trouble for
> > this piece of code in TransactionIdIsInProgress:
>
> > if (TransactionIdPrecedes(xid, RecentXmin))
> > return false;
>
> Hmm ... I suppose it's possible that that happens if the listening
> backend isn't executing any SQL commands but is just sitting.
> While that might describe your test harness, does it describe any
> real-world application?
I think it's not totally unreasonable to have processes sitting idle for
long periods of time. One example: a pooler configured to have more
connections that are actually needed most of the time (I'm fairly sure
I've seen this). Would they not recompute RecentXmin if they did a
sinval reset? Also, a listener daemon for which notifications are very
infrequent.
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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To: pgsql-bugs@postgresql.org
Cc: alvherre@alvh.no-ip.org, tgl@sss.pgh.pa.us, marko@joh.to, michael.paquier@gmail.com
Subject: Re: BUG #14830: Missed NOTIFications, PostgreSQL 9.1.24
In-Reply-To: <20171010140621.u4avva4cxylwpyew@alvherre.pgsql>
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