Thread: BUG #3495: PostgreSQL does not use POSIX SHM or SEM in place of SYSV equivalents
BUG #3495: PostgreSQL does not use POSIX SHM or SEM in place of SYSV equivalents
From
"Roger Leigh"
Date:
The following bug has been logged online: Bug reference: 3495 Logged by: Roger Leigh Email address: rleigh@whinlatter.ukfsn.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
Re: BUG #3495: PostgreSQL does not use POSIX SHM or SEM in place of SYSV equivalents
From
Heikki Linnakangas
Date:
Roger Leigh wrote: > The following bug has been logged online: Not a bug, but a feature request... > PostgreSQL is using the old SYSV shared memory and semaphores, as evidenced > by ipcs: > ... > 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: > ... > Having the option of utilising either form of shared memory would be rather > useful. A patch to do that submitted was submitted in Spring, but it was not accepted for 8.3 because there was some issues with it. Search the archives for more details. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com
Re: BUG #3495: PostgreSQL does not use POSIX SHM or SEM in place of SYSV equivalents
From
Tom Lane
Date:
Heikki Linnakangas <heikki@enterprisedb.com> writes:
> Roger Leigh wrote:
>> PostgreSQL is using the old SYSV shared memory and semaphores, as evidenced
>> by ipcs:
> A patch to do that submitted was submitted in Spring, but it was not
> accepted for 8.3 because there was some issues with it.
More strongly: it never will be accepted because the POSIX API doesn't
offer the features we need.
You can use POSIX semaphores if you choose (there are compile options
for that), but experience to date says that that degrades performance.
POSIX shared memory is simply not happening.
regards, tom lane