Re: FATAL: bogus data in lock file "postmaster.pid": ""

On Thu, Jan 5, 2012 at 17:13, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> writes:
>> My laptop ran out of battery and turned itself off while I was just
>> starting up postmaster. After plugging in the charger and rebooting, I
>> got the following error when I tried to restart PostgreSQL:
>
>> FATAL:  bogus data in lock file "postmaster.pid": ""
>
>> postmaster.pid file was present in the data directory, but had zero
>> length. Looking at the way the file is created and written, that can
>> happen if you crash after the file is created, but before it's
>> written/fsync'd (my laptop might have write-cache enabled, which would
>> make the window larger).
>
>> I was a bit surprised by that. That's probably not a big deal in
>> practice, but I wonder if there was some easy way to avoid that. First I
>> thought we could create the new postmaster.pid file with a temporary
>> name and rename it in place, but rename(2) will merrily overwrite any
>> existing file which is not what we want. We could use link(2), I guess.
>
> I think link(2) would create race conditions of its own.  I'd be
> inclined to suggest that maybe we should just special-case a zero length
> postmaster.pid file as meaning "okay to proceed".  In general, garbage

That's pretty much what I meant - but with a warning message.

> data in postmaster.pid is something I'm happy to insist on manual
> recovery from, but maybe we could safely make an exception for empty
> files.

+1.

--
 Magnus Hagander
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