Re: POSIX shared memory redux

On Sun, Apr 10, 2011 at 5:03 PM, A.M. <agentm@themactionfaction.com> wrote:
> To ensure that no two postmasters can startup in the same data directory, I use fcntl range locking on the data directory lock file, which also works properly on (properly configured) NFS volumes. Whenever a postmaster or postmaster child starts, it acquires a read (non-exclusive) lock on the data directory's lock file. When a new postmaster starts, it queries if anything would block a write (exclusive) lock on the lock file which returns a lock-holding PID in the case when other postgresql processes are running.

This seems a lot leakier than what we do now (imagine, for example,
shared storage) and I'm not sure what the advantage is.  I was
imagining keeping some portion of the data in sysv shm, and moving the
big stuff to a POSIX shm that would operate alongside it.

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