Finding size of postgres shared memory segment on CentOS 6.3

Question

I am trying to debug some shared memory issues with Postgres 9.3.1 and CentOS release 6.3 (Final). Using top, I can see that many of the postgres connections are using shared memory:

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 3534 postgres  20   0 2330m 1.4g 1.1g S  0.0 20.4   1:06.99 postgres: deploy mtalcott 10.222.154.172(53495) idle
 9143 postgres  20   0 2221m 1.1g 983m S  0.0 16.9   0:14.75 postgres: deploy mtalcott 10.222.154.167(35811) idle
 6026 postgres  20   0 2341m 1.1g 864m S  0.0 16.4   0:46.56 postgres: deploy mtalcott 10.222.154.167(37110) idle
18538 postgres  20   0 2327m 1.1g 865m S  0.0 16.1   2:06.59 postgres: deploy mtalcott 10.222.154.172(47796) idle
 1575 postgres  20   0 2358m 1.1g 858m S  0.0 15.9   1:41.76 postgres: deploy mtalcott 10.222.154.172(52560) idle 
  ...

There are about 29 total idle connections. However, sudo ipcs -m only shows:

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x0052e2c1 163840     postgres   600        48         21

Surprisingly, it only shows it using 48 bytes. Why doesn't ipcs show a larger segment? Is there a different command I should be using?

Answer 1

I think it is because your postgre is of version 9.3, which uses POSIX type of shared memory. And ipcs -m shows sysV shared memory segments, which were used in Postgre of prior versions.