Date: Sun, 29 May 2022 10:01:57 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: "James Pang (chaolpan)" <chaolpan@cisco.com>
Cc: pgsql-performance@lists.postgresql.org
Subject: Re: postgres backend process hang on " D " state
Message-ID: <20220529150157.GM19626@telsasoft.com>
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On Sun, May 29, 2022 at 01:20:12PM +0000, James Pang (chaolpan) wrote:
>    We have a performance test on Postgresql 13.4 on RHEL8.4 , just after connection storm in ( 952 new connections coming in 1 minute),  a lot of backends start on " D " state,  and when more sessions got disconnected, they do not exit successfully, instead became  "defunct".   No errors from postgresql.log , just after the connection storm, some pg_cron workers can not started either.  The server is a Virtual machine and no IO hang (actually) IO load is very low.   Could be a postgresql bug or an OS abnormal behavior?

What settings have you set ?
https://wiki.postgresql.org/wiki/Server_Configuration

What extensions do you have loaded?  \dx

Send the output of SELECT * FROM pg_stat_activity either as an attachment or in
\x mode?

What is your data dir ?  Is it on the VM's root filesystem or something else ?
Show the output of "mount".  Are there any kernel messages in /var/log/messages
or `dmesg` ?

How many relations are in your schema ?
Are you using temp tables ?
Long-running transactions ?

-- 
Justin