Re: file-locking and postmaster.pid

On Tue, May 23, 2006 at 05:23:16PM +0200, Andreas Joseph Krogh wrote:
> Hi all.
>
> I've experienced several times that PG has died somehow and the postmaster.pid
> file still exists 'cause PG hasn't had the ability to delete it upon proper
> shutdown. Upon start-up, after such an incidence, PG tells me another PG is
> running and that I either have to shut down the other instance, or delete the
> postmaster.pid file if there really isn't an instance running. This seems
> totally unnecessary to me. Why doesn't PG use file-locking to tell if another
> PG is running or not? If PG holds an exclusive-lock on the pid-file and the
> process crashes, or shuts down, then the lock(which is process-based and
> controlled by the kernel) will be removed and another PG which tries to start
> up can detect that. Using the existence of the pid-file as the only evidence
> gives too many false positives IMO.

Well, maybe you could tweak postgres startup script, add check for post
master (either 'pgrep postmaster' or 'ps -axu | grep [p]ostmaster'), and
delete pid file on negative results.

i.e.

#!/bin/bash
PID=`pgrep -f /usr/bin/postmaster`;

if [[ $PID ]]; then
echo "'$PID'";
# postgres is already running
else
echo "Postmaster is not running";
# delete stale PID file
fi