Re: Troubleshooting a segfault and instance crash

Hi Pavel,

I don’t have a core yet, the only way I have now is to intentionally crash the prod system a couple of times. Haven’t resorted to that yet.

Interesting you mentioned pgaudit—it is installed on this system because that is a our standard installation but on this particular system we haven’t yet needed audits so the audit role is ‘empty’. (And on a different system with same installation and heavy of audit we’ve seen no segfaults)

On this system

pgaudit.role = 'auditor'
pgaudit.log_parameter = off
pgaudit.log_catalog = off
pgaudit.log_statement_once = on
pgaudit.log_level = log

select * from information_schema.role_table_grants where grantee = 'auditor';
(0 rows)

thanks, Blair

From: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
Date: Thursday, March 8, 2018 at 9:49 AM
To: Blair Boadway <bboadway(at)abebooks(dot)com>
Cc: "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org>
Subject: Re: Troubleshooting a segfault and instance crash

Hi

2018-03-08 18:40 GMT+01:00 Blair Boadway <bboadway(at)abebooks(dot)com<mailto:bboadway(at)abebooks(dot)com>>:
Hello,

We’re seeing an occasional segfault on a particular database

Mar 7 14:46:35 pgprod2 kernel:postgres[29351]: segfault at 0 ip 000000302f32868a sp 00007ffcf1547498 error 4 in libc-2.12.so<http://libc-2.12.so>[302f200000+18a000]
Mar 7 14:46:35 pgprod2 POSTGRES[21262]: [5] user=,db=,app=client= LOG: server process (PID 29351) was terminated by signal 11: Segmentation fault

It crashes the database, though it starts again on its own without any apparent issues. This has happened 3 times in 2 months and each time the segfault error and memory address is the same. We’ve only seen it on one database, though we’ve seen it on both hosts of primary/standby setup—we switched over primary to other host and got a segfault there, which seems to eliminate a hardware issue. Oddly the database has no issues for normal DML workloads (it is a moderately busy prod oltp system) but the segfault has happened very shortly after DML changes are made. Most recently it happened while running a series of grants for new db users we were deploying (ie. running a sql script from psql on the primary host)

grant usage on schema app to app_user1;
grant usage on schema app to app_user2;
...

Our set up is
RHEL 6.9 - 2.6.32-696.16.1.el6.x86_64
PostgreSQL 9.6.5 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-18), 64-bit
Extensions - pg_cron,repmgr_funcs,pgaudit,pg_stat_statements,pg_hint_plan,pglogical

So far can’t reproduce on a test system, have just added some OS config to collect core from the OS but haven’t collected a core yet. There isn’t any particular config change or extension that we can link to the problem, this is a system that has run for months without problems since last config changes. Appreciate any ideas.

can you get core dump? It can be pgaudit bug maybe? It is complex extension.
Regards

Pavel

Regards,
Blair