[nycbug-talk] postgres memory question

[Jonathan Vanasco]

the other day i noticed what might be a memory leak in PG on my  
FreeBSD 6.0 REL box ( it could be in Apache/ModPerl/DBI , but some  
bad command line tests point to pg.  I'm hoping someone here can help  
me figure out what is at blame )

someone else running modperl with pg on RHEL posted a problem like  
this a few weeks ago,  so I think there might be more to it...

anyways, here's the issue:

i start my box up, ONLY running apache/pg ( nothing else is on ), and  
I have ~900 MB free.   Perfect.
I make some requests, Apache and PG consume memory.   Expected.
I restart Apache, it releases memory and the associated pg_client .   
PG still holds shared memory.  Expected.
I start stressing Apache  ( 10k-50k requests )- apache works great.   
not visible memory issues.  MaxChildRequests keeps size manageble.
I stop apache, it releases memory and the associated pg_client  
memory.  PG still holds shared memory.  Expected.
I stop the postmaster daemon.  PG releases the lock on shared memory  
( ipcs shows it ).  I expect to see 900 MB free.  Instead i see 700.

When I noticed this first, I was swapping.  The  first person who  
experienced something like this was swapping like mad as well.

I run this again a few times, I inch closer and closer to 0.  Except  
its hard to get the free mem down to 0 - it takes a while.

I'm hoping some people here might be able to suggest the following:
	a- 	A pure PG way to max out shared memory in clients, and restart,  
so I can tell if this behavior is from PG or Apache/ModPerl.  I  
*think* its from PG, as start/stop a few pg clients and then stop/ 
start the daemon i see a decrease in memory.
		I was trying to think of some sort of recursive select or  
exponential  algorithm.  I couldn't find anything on google though.

	b- 	A way to better examine free memory.  My knowledge is limited to  
top / and a little bit of libgtop.  I know i was swapping because top  
reported it as such.  But I've been told that top doesn't always  
report truly 'free' memory-- once that hits 0 it looks in buffers/ 
cached.  So maybe the pg memory is there?  I dunno.

If anyone has a clue, I'd be appreciative.  This isn't an issue as  
long as I don't stop/start postgres.