From: Tom Lane <tgl@sss.pgh.pa.us>
To: neeraj kumar <neeru.cse@gmail.com>
cc: pgsql-admin@postgresql.org, pgsql-general@postgresql.org
Subject: Re: Query on pg_stat_activity table got stuck
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Comments: In-reply-to neeraj kumar <neeru.cse@gmail.com>
	message dated "Wed, 08 May 2019 10:42:12 -0700"
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Date: Wed, 08 May 2019 14:12:56 -0400
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neeraj kumar <neeru.cse@gmail.com> writes:
> Took some time to get stack trace as we didn't had root permission.
> Attaching stack trace of two process (out of many) stuck for same query
> below[1][2]

Hmm, the line numbers in your stack traces don't agree with either v10
or HEAD branches for me.  But assuming that you've correctly identified
where it's stuck:

> Seems like call is unable to come out of this loop :
> https://github.com/postgres/postgres/blob/master/src/backend/postmaster/=
pgstat.c#L3361-L3400

the only really obvious theory is that some process left its
st_changecount odd, which would more or less have to imply that
something threw an error between pgstat_increment_changecount_before
and pgstat_increment_changecount_after.  There's only one place
where that seems very plausible, namely pgstat_bestart, which is
doing a rather scary amount of stuff in between.  Are you using
either SSL or GSS?

			regards, tom lane