postgres shared_buffers memory appears private

Question

I increased postgres shared_buffers to 7GB on a Linux machine. This is about 25% of the available RAM on this machine which I believe follows the postgres recommendation.

Memory on the machine exhausted. What I see is man postgres processes each using 7GB resident memory.When I run top I see the memory on the machine being fully used so I think the 7GB is private memory of the postmaster processes.

I thought shared_buffers memory is supposed to be shared.

This is postgres 8

PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
15872 postgres  15   0 7481m 7.2g 7.1g S 17.6 15.2  43:19.92 postgres: st stk 127.0.0.1(60729) SELECT
3467 postgres  15   0 7489m 7.2g 7.1g S 15.9 15.2  56:33.33 postgres: st stk 127.0.0.1(44351) SELECT
9484 postgres  15   0 7495m 7.2g 7.1g S 15.0 15.2 206:31.23 postgres: st stk 127.0.0.1(42126) SELECT
19090 postgres  15   0 7495m 7.2g 7.1g S 14.2 15.2 155:23.52 postgres: st stk 127.0.0.1(43897) SELECT
14857 postgres  16   0 7485m 7.2g 7.1g D 10.9 15.2  36:12.30 postgres: st stk 127.0.0.1(52229) SELECT
15862 postgres  15   0 7495m 7.2g 7.1g S 10.0 15.2 146:18.47 postgres: st stk 127.0.0.1(60728) SELECT
9485 postgres  16   0 7488m 7.2g 7.1g S  3.3 15.2 191:53.33 postgres: st stk 127.0.0.1(42127) SELECT

Craig Ringer · Accepted Answer · 2014-02-25 07:59:04Z

1

shared_buffers appear to be mapped into RSS on Linux when the page is mapped into a process's address space by a read or write operation to it.

The RAM is in fact shared, it's just how Linux accounts for the RAM and how top displays it that's an issue.

http://wiki.postgresql.org/wiki/FAQ#Why_does_PostgreSQL_use_so_much_memory.3F

answered Feb 25, 2014 at 7:59

Craig Ringer

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