Re: [PATCHES] POSIX shared memory support

[Chris Marcellino]

In case you haven't had enough, here is another version of the code to make Postgres use POSIX shared memory. Along with the issues that have already been addressed, this version ensures that orphaned backends are not in the database when restarting Postgres by using a single 1 byte SysV segment to see who is attached to the segment using shmctl/IPC_STAT/nattach.

Thanks again,
Chris Marcellino

This effectively frees Postgres from the SHMMAX and SHMALL limits. Since this still takes one SysV segment, SHMMNI can still be reached on most platforms if a ton of databases are opened simultaneously (i.e. 32 on Mac OS X, 256 on Linux and Solaris). If you have the need to ship a product with Postgres embedded in it and are unable to change kernel settings (like myself), this might be of use to you. I have tested all of the failure situations I could think of by various combinations of deleting lockfiles while in use, changing the PID inside the lockfile and trying to restart and run more than one postmaster simultaneously. Of course, this since this requires both POSIX and SysV shared memory, this doesn't increase the portability of Postgres which might make it less appropriate for mass distribution; I thought I would put it out there for any feedback either way.

posix_shmem.c
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TIP 2: Don't 'kill -9' the postmaster