I've seen a couple references to using ipcs to help properly size shared_buffers.
I don't claim to be a SA guru, so could someone help explain how to interpret the output of ipcs and how that relates to shared_buffers? How does one determine the size of the segment arrays? I see the total size using ipcs -m which is roughly shared_buffers * 8k.
I tried all of the dash commands in the ipcs man page, and the only one that might give a clue is ipcs -t which shows the time the semaphores were last used. If you look at the example I give below, it appears as if I'm only using 4 of the 17 semaphores (PG was started on Oct 8).
Am I correct in assuming that if the arrays are all the same size then I should only need about 1/4 of my currently allocated shared_buffers?
------ Shared Memory Operation/Change Times --------
shmid owner last-op last-changed 847183872 postgres Fri Oct 8 11:03:31 2004 Fri Oct 8 11:03:31 2004 847216641 postgres Fri Oct 8 11:03:31 2004 Fri Oct 8 11:03:31 2004 847249410 postgres Fri Oct 8 11:03:31 2004 Fri Oct 8 11:03:31 2004 847282179 postgres Fri Oct 8 11:03:31 2004 Fri Oct 8 11:03:31 2004 847314948 postgres Fri Oct 8 11:03:31 2004 Fri Oct 8 11:03:31 2004 847347717 postgres Fri Oct 8 11:03:31 2004 Fri Oct 8 11:03:31 2004 847380486 postgres Fri Oct 8 11:03:31 2004 Fri Oct 8 11:03:31 2004 847413255 postgres Fri Oct 8 11:03:31 2004 Fri Oct 8 11:03:31 2004 847446024 postgres Fri Oct 8 11:03:31 2004 Fri Oct 8 11:03:31 2004 847478793 postgres Fri Oct 8 11:03:31 2004 Fri Oct 8 11:03:31 2004 847511562 postgres Fri Oct 8 11:03:31 2004 Fri Oct 8 11:03:31 2004 847544331 postgres Fri Oct 8 11:03:31 2004 Fri Oct 8 11:03:31 2004 847577100 postgres Fri Oct 8 11:03:31 2004 Fri Oct 8 11:03:31 2004 847609869 postgres Fri Oct 15 11:34:28 2004 Fri Oct 15 11:34:29 2004 847642638 postgres Fri Oct 15 11:33:35 2004 Fri Oct 15 11:33:35 2004 847675407 postgres Fri Oct 15 11:34:28 2004 Fri Oct 15 11:34:29 2004 847708176 postgres Fri Oct 15 11:27:17 2004 Fri Oct 15 11:32:20 2004
Also, isn't the shared memory supposed to show up in free? Its always showing as 0:
# free
total used free shared buffers cached
Mem: 3896928 3868424 28504 0 59788 3605548
-/+ buffers/cache: 203088 3693840
Swap: 1052216 16 1052200Thanks!
---------------------------(end of broadcast)--------------------------- TIP 7: don't forget to increase your free space map settings
