Date: Tue, 18 Feb 2020 18:58:57 +0100
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Nagaraj Raj <nagaraj.sf@yahoo.com>
Cc: Pgsql-general <pgsql-general@postgresql.org>,
	PgAdmin Support <pgadmin-support@postgresql.org>,
	PostgreSQL Hackers <pgsql-hackers@postgresql.org>,
	"pgsql-hackers-owner@postgresql.org" <pgsql-hackers-owner@postgresql.org>,
	Postgres Performance List <pgsql-performance@postgresql.org>,
	Pg Bugs <pgsql-bugs@postgresql.org>,
	Pgsql-admin <pgsql-admin@postgresql.org>,
	Pgadmin-hackers <pgadmin-hackers@postgresql.org>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
	Pgsql-pkg-yum <pgsql-pkg-yum@postgresql.org>
Subject: Re: DB running out of memory issues after upgrade
Message-ID: <20200218175857.5rsxovq5zxmr4wxi@development>
References: <1425420656.4660607.1582047988379.ref@mail.yahoo.com>
 <1425420656.4660607.1582047988379@mail.yahoo.com>
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On Tue, Feb 18, 2020 at 05:46:28PM +0000, Nagaraj Raj wrote:
>after upgrade Postgres to v9.6.11 from v9.6.9 DB running out of memory issues no world load has changed before and after upgrade. 
>
>spec: RAM 16gb,4vCore
>Any bug reported like this or suggestions on how to fix this issue? I appreciate the response..!! 
>

This bug report (in fact, we don't know if it's a bug, but OK) is
woefully incomplete :-(

The server log is mostly useless, unfortunately - it just says a bunch
of processes were killed (by OOM killer, most likely) so the server has
to restart. It tells us nothing about why the backends consumed so much
memory etc.

What would help us is knowing how much memory was the backend (killed by
OOM) consuming, which should be in dmesg.

And then MemoryContextStats output - you need to connect to a backend
consuming a lot of memory using gdb (before it gets killed) and do

  (gdb) p MemoryContextStats(TopMemoryContext)
  (gdb) q

and show us the output printed into server log. If it's a backend
running a query, it'd help knowing the execution plan.

It would also help knowing the non-default configuration, i.e. stuff
tweaked in postgresql.conf.

regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services