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Re: auto_explain causes cluster crash if pg_ctl reload is used (not pg_ctl restart)

From: bricklen <bricklen(at)gmail(dot)com>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: pgsql-bugs(at)postgresql(dot)org
Subject: Re: auto_explain causes cluster crash if pg_ctl reload is used (not pg_ctl restart)
Date: 2011-10-25 19:51:28
Message-ID: CAGrpgQ8C4aXYrW3TdtCKZURTYfsyh5jF8RdBxt7b+LXcgwu7TA@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-bugs
On Tue, Oct 25, 2011 at 9:22 AM, Heikki Linnakangas
<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
> On 25.10.2011 18:42, bricklen wrote:
>>
>> Tried on both
>> PostgreSQL 9.0.4 on x86_64-unknown-linux-gnu, compiled by GCC gcc
>> (GCC) 4.1.2 20080704 (Red Hat 4.1.2-48), 64-bit
>> and
>> PostgreSQL 9.0.3 on x86_64-unknown-linux-gnu, compiled by GCC gcc
>> (GCC) 4.1.2 20080704 (Red Hat 4.1.2-48), 64-bit
>>
>> shared_preload_libraries = 'pg_stat_statements,auto_explain'
>> custom_variable_classes = 'auto_explain'
>> auto_explain.log_min_duration = '10s'
>> auto_explain.log_analyze = true
>> auto_explain.log_buffers = true
>>
>> I was testing to see if any of the settings above got applied after
>> issuing a "pg_ctl reload" rather than a restart, and I was surprised
>> to see that I could crash my db cluster. I realize that the docs say
>> to issue a restart, but the crash seems a tad user-unfriendly.
>>
>> Any other details I should provide?
>
> A backtrace from the core dump would be help a lot. Can you get one? More
> precise instructions on how to reproduce this would also be nice.

I tried generating a core dump according to the steps at
http://wiki.postgresql.org/wiki/Getting_a_stack_trace_of_a_running_PostgreSQL_backend_on_Linux/BSD
but either I was doing it incorrectly, or it wasn't dumping core
anywhere I could find.

The steps to reproduce are pretty simple.

Set the following in the postgresql.conf file:

shared_preload_libraries = 'pg_stat_statements,auto_explain'
custom_variable_classes = 'auto_explain'
auto_explain.log_min_duration = '10s'
auto_explain.log_analyze = true
auto_explain.log_buffers = true

As the postgres user, issue "pg_ctl reload"

pg_ctl status will now show that there is no running postmaster.  I
won't have access to those servers for at least another couple of
hours, but if there are some steps I should try to get a core dump I'm
willing to try them when the servers are free again.

The servers are running on CentOS 5.7 and CentOS 5.6, with the
packages from http://yum.pgrpms.org/9.0/redhat/

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