RE: postgres backend process hang on " D " state

1. extensions
      shared_preload_libraries = 'orafce,pgaudit,pg_cron,pg_stat_statements,set_user'
2.  psql can not login now ,it hang there too, so can not check anything from pg_stats_* views
3.  one main app user and 2 schemas ,no long running transactions .
4. we use /pgdata , it's on xfs , lvm/vg RHEL8.4 ,it's a shared storage, no use root filesystem.
/dev/mapper/pgdatavg-pgdatalv     500G  230G  271G  46% /pgdata
/dev/mapper/pgdatavg-pgarchivelv  190G  1.5G  189G   1% /pgarchive
/dev/mapper/pgdatavg-pgwallv      100G   34G   67G  34% /pgwal

Regards,

James
-----Original Message-----
From: Justin Pryzby <pryzby@telsasoft.com>
Sent: Sunday, May 29, 2022 11:02 PM
To: James Pang (chaolpan) <chaolpan@cisco.com>
Cc: pgsql-performance@lists.postgresql.org
Subject: Re: postgres backend process hang on " D " state

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
comingin 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
workerscan not started either.  The server is a Virtual machine and no IO hang (actually) IO load is very low.   Could
bea 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