"Rainer Bauer" <[EMAIL PROTECTED]> writes: > Greg Smith wrote: > >>Was working on some documentation today and I realized that I've taken for >>granted the lore about not using large values for shared_buffers in >>Windows without ever understanding why. Can someone explain what the >>underlying mechanism that causes that limitation is? From poking the >>archives I got the impression it was some page mapping issue but details >>are elusive. > > All I can offer is Magnus' explanation: "All evidence I've seen points to that > you should have shared_buffers as *small* as possible on win32, because memory > access there is slow. And leave more of the caching up to the OS." > <http://archives.postgresql.org/pgsql-general/2007-10/msg01115.php>
Details are elusive because we have no idea *why* memory access should be slow. If the pages are all in core and mapped in the memory map then really accessing them should just be a hardware issue. The OS only gets involved with a page needs to be paged in from swap or other backing store. One thing which comes to mind is that it's possible Windows is swapping out shared memory making having large shared memory segments dangerous on that front. Of course it's also possible something more subtle is going on. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com Ask me about EnterpriseDB's Slony Replication support! -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
