Shared Memory Leakage

Symptom

The following error information is recorded in logs.

This error usually means that PostgreSQL's request for a shared  memory segment 
exceeded available memory or swap space,  or exceeded your kernel's SHMALL parameter.  
You can either  reduce the request size or reconfigure the kernel with larger SHMALL.

Cause Analysis

Run the free command to check the memory usage. It is found that the shared memory occupies a large part.

# free -g
              total        used        free      shared  buff/cache   available
Mem:             31           1           2          23         27         2
Swap:             3           3           0

Run the ipcs command to check the usage of the shared memory. It is found that there is a large amount of shared memory that is not used by processes but is not reclaimed. That is, the value of nattch is 0.

[root@pekpeuler00671 script]# ipcs -m

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x00000000 65536      gnome-init 777        16384      1          dest
0x00000000 131073     gnome-init 777        16384      1          dest
0x00000000 163842     gnome-init 777        3145728    2          dest
0x00000000 393219     gnome-init 600        524288     2          dest
0x00000000 425988     gnome-init 600        4194304    2          dest
0x00000000 458757     gnome-init 777        3145728    2          dest
0x00f42401 3604486    1001       600        4455342080 0
0x00f42402 14123015   1003       600        4457177088 0
0x00f42403 23592968   1005       600        4457177088 0
0x00f42404 33062921   1007       600        4457177088 0
0x00f42405 42532874   1009       600        4457177088 0
0x00f42406 52002827   1011       600        4457177088 0
0x00f42407 61472780   1013       600        4457177088 0
0x00f42408 70942733   1015       600        4457177088 0
0x00f42409 80412686   1017       600        4457177088 0
0x00f4240a 89882639   1019       600        4457177088 0
0x00f4240b 99352592   1021       600        4457177088 0
0x00f4240c 108822545  1023       600        4457177088 0
0x00f4240d 118292498  1025       600        4457177088 0
0x00f4240e 127762451  1027       600        4457177088 0
0x00f4240f 136904724  1029       600        4455342080 0
0x00f42410 146374677  1031       600        4457177088 0
0x00f42411 155844630  1033       600        4457177088 0
0x00f42412 165314583  1035       600        4457177088 0
0x00f42413 174784536  1037       600        4457177088 0

The cause is that the kill -9 command is run to exit the database process and the IpcMemoryDelete function is not invoked to clear the shared memory. As a result, the memory leakage occurs.

Procedure

Run the ipcrm command to release the shared memory without owners. For example, to release the shared memory whose shmid is 3604486, run the following command.

ipcrm -m shid3604486