Re: circular wait not triggering deadlock ?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Justin Pryzby <pryzby(at)telsasoft(dot)com>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: circular wait not triggering deadlock ?
Date: 2018-03-08 20:05:36
Message-ID: 25504.1520539536@sss.pgh.pa.us
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Justin Pryzby <pryzby(at)telsasoft(dot)com> writes:
> On Thu, Mar 08, 2018 at 01:57:06PM -0500, Tom Lane wrote:
>> PID 20488 is evidently waiting for PID 6471 to finish its transaction.
>> What's that one doing?

> Um, I thought I had kept track of all two pids but looks not..
> query | SELECT pg_export_snapshot();

pg_export_snapshot doesn't block for other transactions, though.
Further down, you have output that confirms that:

> 6471 | idle in transaction | psql | SELECT pg_export_snapshot();

That SELECT is the most recently completed command, not the current one.
So now the question is what the connected application is waiting for
before committing.

regards, tom lane

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