Re: Weaker shmem interlock w/o postmaster.pid - Mailing list pgsql-hackers

From Robert Haas
Subject Re: Weaker shmem interlock w/o postmaster.pid
Date
Msg-id CA+TgmoZJn7oF8uOQva4sBY=G04UHZ23+p=tjE9NueZsBvHMTFQ@mail.gmail.com
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In response to Weaker shmem interlock w/o postmaster.pid  (Noah Misch <noah@leadboat.com>)
Responses Re: Weaker shmem interlock w/o postmaster.pid
List pgsql-hackers
On Tue, Sep 10, 2013 at 11:33 PM, Noah Misch <noah@leadboat.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



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