Re: Unkillable Backend Processes

Thomas F. O'Connell wrote:

> When I kill these off individually using kill and then shut down the
> postmaster with pg_ctl immediate mode, I will occasionally find a
> backend process that cannot be killed, even with a KILL (-9) signal.
>
> Is this likely to be caused by something at a lower level than postgres?

Nothing Postgres does is able to block a SIGKILL (-9) signal. You can
be certain that it is stuck in a system call, most likely reading
something from disk.

> Here are the specs:
>
> PostgreSQL 8.1.3
> pgpool 3.0.1
> Debian GNU/Linux 3.1
> Linux 2.6.10 #8 SMP
> system: ext3 RAID 1
> WAL: jfs RAID 10
> data: jfs RAID 10
>
> There's also an NFS mount point.

JFS is not a very common sight around here I think. And NFS mounts are
known as troublemakers of filesystem-level problems.

> I'm still trying to do the forensics on the root cause (a related
> oddity: the system can run in production for days or weeks without
> any issues), but I'm just as interested in why I can't kill postgres
> backend processes that have no postmaster.

Backend processes are pretty much independent from postmaster. If you
SIGKILL the postmaster, backends will happily continue with life AFAIK.
(And anyway, if you can't kill them with SIGKILL, the postmaster won't
be able to either.)

--
Alvaro Herrera http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support