The realtime preemption mini-summit

Posted Sep 28, 2009 22:42 UTC (Mon) by flewellyn (subscriber, #5047)
In reply to: The realtime preemption mini-summit by nix
Parent article: The realtime preemption mini-summit

>> SYSV IPC is best avoided.

>Not just in realtime situations, of course.

Tell that to the PostgreSQL people. They use SYSV shared memory and semaphores in the database. It's quite efficient and works well.

Of course, an RDBMS is not a realtime application, but you claimed that it should be avoided in other situations as well.

The realtime preemption mini-summit

Posted Sep 29, 2009 9:21 UTC (Tue) by nix (subscriber, #2304) [Link] (4 responses)

Yes. I don't really know why databases use SysV SHM: the API for all the SysV stuff is so cracksmoking and unpleasant and non-Unixlike. I suppose POSIX shared memory functions didn't exist when PostgreSQL was young, and mmap() of /dev/null wasn't very portable at that point... so maybe it's just history.

The realtime preemption mini-summit

Posted Sep 29, 2009 14:58 UTC (Tue) by flewellyn (subscriber, #5047) [Link]

Well, the SysV stuff for a lot of things is unpleasant to work with. Still, it does work.

POSIX shmem in PostgreSQL

Posted Sep 29, 2009 19:50 UTC (Tue) by alvherre (subscriber, #18730) [Link] (2 responses)

It's not just history. In fact, a patch was posted to add support for POSIX shmem, but as it turns out, the POSIX API is not complete enough for PostgreSQL's purposes. See here, for instance: http://archives.postgresql.org/pgsql-patches/2007-02/msg0...

POSIX shmem in PostgreSQL

Posted Sep 29, 2009 22:47 UTC (Tue) by alvherre (subscriber, #18730) [Link]

BTW, mmap does not work either.

POSIX shmem in PostgreSQL

Posted Sep 30, 2009 15:14 UTC (Wed) by nix (subscriber, #2304) [Link]

Oh, curses. We need a POSIX syscall that does what lsof/fuser do, really.