Re: Weaker shmem interlock w/o postmaster.pid

On Tue, Sep 10, 2013 at 11:33 PM, Noah Misch <noah(at)leadboat(dot)com> wrote:
> I'm thinking to preserve postmaster.pid at immediate shutdown in all released
> versions, but I'm less sure about back-patching a change to make
> PGSharedMemoryCreate() pickier. On the one hand, allowing startup to proceed
> with backends still active in the same data directory is a corruption hazard.
> On the other hand, it could break weird shutdown/restart patterns that permit
> trivial lifespan overlap between backends of different postmasters. Opinions?

I'm more sanguine about the second change than the first. Leaving
postmaster.pid around seems like a clear user-visible behavior change
that could break user scripts or have other consequences that we don't
foresee; thus, I would vote against back-patching it. Indeed, I'm not
sure it's a good idea to do that even in master. On the other hand,
tightening the checks in PGSharedMemoryCreate() seems very much worth
doing, and I think it might also be safe enough to back-patch.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company