Manipulating disk cache (buf) settings

John-Mark Gurney gurney_j at
Mon May 23 16:30:04 PDT 2005

Vivek Khera wrote this message on Mon, May 23, 2005 at 17:17 -0400:
> On May 23, 2005, at 1:44 PM, John-Mark Gurney wrote:
> >This is incorrect...  FreeBSD merged the vm and buf systems a while  
> >back,
> >so all of memory is used as a disk cache..  The buf cache is still  
> >used
> >for filesystem meta data (and for pending writes of files, but  
> >those buf's
> >reference the original page, not local storage)...
> >
> Cool... So what would you recommend telling an application like  
> Postgres what the cache size is?  All of RAM?  That seems unlikely  
> given much of the ram is used for other things.  Is there no upper  
> bound in how much RAM will be used for the cache?

I'm not familar host Postgres uses the cache number to change it's
behavior, but I would say choose a responable amount of memory that
you expect to regularly have available on the system...   If you are
only using it for db, and a few other small processes, 512meg less
than ram is probably reasonable...

The other way is to try a few different values and see how it impacts

  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."

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