BUG #3495: PostgreSQL does not use POSIX SHM or SEM in place of SYSV equivalents

The following bug has been logged online:

Bug reference: 3495
Logged by: Roger Leigh
Email address: rleigh(at)whinlatter(dot)ukfsn(dot)org
PostgreSQL version: 8.2.4
Operating system: Debian GNU/Linux (glibc 2.6, linux 2.6.22)
Description: PostgreSQL does not use POSIX SHM or SEM in place of
SYSV equivalents
Details:

PostgreSQL is using the old SYSV shared memory and semaphores, as evidenced
by ipcs:

% sudo ipcs

------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x0052e2c1 0 postgres 600 29384704 2

------ Semaphore Arrays --------
key semid owner perms nsems
0x0052e2c1 0 postgres 600 17
0x0052e2c2 32769 postgres 600 17
0x0052e2c3 65538 postgres 600 17
0x0052e2c4 98307 postgres 600 17
0x0052e2c5 131076 postgres 600 17
0x0052e2c6 163845 postgres 600 17
0x0052e2c7 196614 postgres 600 17

------ Message Queues --------
key msqid owner perms used-bytes messages

However, the SYSV memory limit is set in-kernel and while it can be easily
changed, it is rather less flexible than POSIX SHM support:

% df /dev/shm
Filesystem 1K-blocks Used Available Use% Mounted on
tmpfs 257584 0 257584 0% /dev/shm

On this system, that limit could be increased up to 6 GiB (though the above
would probably be the upper useful limit given that this is VM-backed).

Having the option of utilising either form of shared memory would be rather
useful.

Regards,
Roger