We have had a case where a production cluster was accidentally shut
down by a customer who used Ctrl+C in the same sh session in which
they had (long before) run pg_ctl start.  We have only seen this in
sh on Solaris.  Other shells on Solaris don't behave this way, nor
does sh on tested versions of Linux.  Nevertheless, the problem is
seen on the default shell for a supported OS.

Analysis suggests that this is because the postmaster retains the
process group ID of the original parent (in this case pg_ctl).  If
pg_ctl is run through the setpgrp command a subsequent Ctrl+C in
the sh session does not shut down the PostgreSQL cluster.

On my development Linux machine:

$ ps axfopid,ppid,pgid,command
[ ... ]
 8416     1  8412 /home/kgrittn/pg/master/Debug/bin/postgres -D Debug/data
 8418  8416  8418  \_ postgres: checkpointer process
 8419  8416  8419  \_ postgres: writer process
 8420  8416  8420  \_ postgres: wal writer process
 8421  8416  8421  \_ postgres: autovacuum launcher process
 8422  8416  8422  \_ postgres: stats collector process
 8427  8416  8427  \_ postgres: kgrittn test [local] idle

All of the PPID values seem correct, and while the PGID values for
backends might initially seem surprising, the commit notes and C
comments here explain why each backend sets up its own process


What is surprising is that the postmaster doesn't set up its own
process group when it is running as a daemon.  We probably don't
want to change that when postgres is run directly from a command
line for development or diagnostic purposes, but Noah suggested
perhaps we should add a --daemonize option which pg_ctl should use
when launching the postmaster, which would cause it to create its
own session group.

Although this is arguably a bug, it seems like it is very rarely
hit and has several workarounds, and any fix would either change
things in a way which might break existing user scripts or would
require a new command-line option; so back-patching a fix to stable
branches doesn't seem appropriate.  I would argue for including a
fix in 9.4 on the basis of it being a bug fix and there being time
to mention it in the release change notes; but I understand the
counter-arguments and realize this is a judgment call.


If the new option seems reasonable, I can draft a patch to
implement that.

Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:

Reply via email to