Re: two shared memory segments?

Ed Loehr <ed(at)loehrtech(dot)com> writes:
> On Wednesday December 21 2005 8:24 pm, Tom Lane wrote:
>> I'd say that you had a backend crash, causing the postmaster
>> to abandon the original shared memory segment and make a new
>> one, but the old segment is still attached to by a couple of
>> processes.

> Does that make sense even if the creating pid is the same for
> both?

Sure. The postmaster survives backend crashes --- that's the point
of having a separate postmaster process at all.

>> There was a bug awhile back whereby the stats support
>> processes failed to detach from shared memory and thus would
>> cause a dead shmem segment to hang around like this. What PG
>> version are you running?

> This is an old 7.3.7 cluster.

[ digs in CVS logs... ] Hmm. AFAICT that bug was fixed in 7.3.5:

2003-11-30 16:56 tgl

* src/: backend/port/sysv_shmem.c, backend/postmaster/pgstat.c,
include/storage/pg_shmem.h (REL7_3_STABLE): Back-patch fix to cause
stats processes to detach from shared memory, so that they do not
prevent the postmaster from deleting the shmem segment during crash
recovery.

You sure it's a 7.3.7 postmaster? Can you dig down to determine exactly
which processes are attached to the older shmem segment?

regards, tom lane