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Re: [HACKERS] Re: postgres memory management

From: Alexander Jerusalem <ajeru(at)gmx(dot)net>
To: Alfred Perlstein <bright(at)wintelcom(dot)net>, Peter Mount <peter(at)retep(dot)org(dot)uk>
Cc: pgsql-general(at)postgresql(dot)org, pgsql-hackers(at)postgresql(dot)org, pgsql-jdbc(at)postgresql(dot)org
Subject: Re: [HACKERS] Re: postgres memory management
Date: 2001-01-22 23:58:49
Message-ID: 4.3.2.7.0.20010123005506.00b76340@pop.gmx.net (view raw or flat)
Thread:
Lists: pgsql-generalpgsql-hackerspgsql-jdbc
At 22:29 22.01.01, Alfred Perlstein wrote:
>* Peter Mount <peter(at)retep(dot)org(dot)uk> [010122 13:21] wrote:
> > At 13:18 21/01/01 +0100, Alexander Jerusalem wrote:
> > >Hi all,
> > >
> > >I'm experiencing some strange behaviour with postgresql 7.0.3 on Red Hat
> > >Linux 7. I'm sending lots of insert statements to the postgresql server
> > >from another machine via JDBC. During that process postgresql 
> continues to
> > >take up more and more memory and seemingly never returns it to the 
> system.
> > >Oddly if I watch the postmaster and it's sub processes in ktop, I can't
> > >see which process takes up this memory. ktop shows that the postgresql
> > >related processes have a constant memory usage but the overall memory
> > >usage always increases as long as I continue to send insert statements.
> > >
> > >When the database connection is closed, no memory is reclaimed, the
> > >overall memory usage stays the same. And when I close down all postgresql
> > >processes including postmaster, it's the same.
> > >I'm rather new to Linux and postgresql so I'm not sure if I should call
> > >this a memory leak :-)
> > >Has anybody experienced a similar thing?
> >
> > I'm not sure myself. You can rule out JDBC (or Java) here as you say you
> > are connecting from another machine.
> >
> > When your JDBC app closes, does it call the connection's close() method?
> > Does any messages like "Unexpected EOF from client" appear on the 
> server side?
> >
> > The only other thing that comes to mine is possibly something weird is
> > happening with IPC. After you closed down postgres, does ipcclean free up
> > any memory?
>
>I don't know if this is valid for Linux, but it is how FreeBSD
>works, for the most part used memory is never free'd, it is only
>marked as reclaimable.  This is so the system can cache more data.
>On a freshly booted FreeBSD box you'll have a lot of 'free' memory,
>after the box has been running for a long time the 'free' memory
>will probably never go higher that 10megs, the rest is being used
>as cache.
>
>The main things you have to worry about is:
>a) really running out of memory (are you useing a lot of swap?)
>b) not cleaning up IPC as Peter suggested.

Thanks for your answer!

I'm rather new to Linux, so I can't tell if it's that way on Linux. But I 
noticed that other programs free some memory when I quit them. But it's 
true that I'm not running out of memory. I have 300 MB of free RAM and no 
swap space is used. As I wrote in reply to Peters mail, ipcclean doesn't 
change anything.

Alexander Jerusalem
ajeru(at)gmx(dot)net
vknn


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