On Fri, 14 Aug 2009, Scott Carey wrote:
The memory used by postgres for shared memory is the largest of all SHR
columns for postgres columns. Or, about 7.9GB. So, postgres is using
about 7.9GB for shared memory, and very little for anything else.
It's a good idea to check this result against the actual shared memory
block allocated. If the server has been up long enough to go through all
of shared_buffers once, the results should be close. You can look at the
block under Linux using "ipcs -m"; the one you want should look something
like this:
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x0052e2c1 21757972 gsmith 600 548610048 10
That represents a bit over 512MB worth of allocated memory for the server.
Alternately, you can use "pmap -d" on a PostgreSQL process to find the
block, something like this works:
$ pmap -d 13961 | egrep "^Address|shmid"
Address Kbytes Mode Offset Device Mapping
96c41000 535752 rw-s- 0000000000000000 000:00009 [ shmid=0x14c0014 ]
I have given up on presuming the summary values top shows are good for
anything on Linux. I look at /proc/meminfo to see how much RAM is free,
and to figure out what's going on with the server processes I use:
ps -e -o pid,rss,vsz,size,cmd | grep postgres
And compute my own totals (one of these days I'm going to script that
process). Useful reading on this topic:
http://virtualthreads.blogspot.com/2006/02/understanding-memory-usage-on-linux.html
http://mail.nl.linux.org/linux-mm/2003-03/msg00077.html
http://forums.gentoo.org/viewtopic.php?t=175419
Most confusion about what's going on here can be resolved by spending some
quality time with pmap.
--
* Greg Smith gsmith@xxxxxxxxxxxxx http://www.gregsmith.com Baltimore, MD
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