Re: [HACKERS] effective_cache_size less than shared_buffers
On Thu, Feb 26, 2009 at 1:33 AM, Joshua D. Drake j...@commandprompt.com wrote: On Wed, 2009-02-25 at 17:04 -0800, Josh Berkus wrote: Joshua D. Drake wrote: I would say no. Although I could see an argument for the default effective_cache_size always being the same size as shared_buffers. That's certainly not what we've meant historically by ECS. Since we are already using X amount of shared_buffers we know we have at least X amount of cache. That's not what you wrote, at least how it was understood. It sounds like you're in violent agreement. We can't determine the size of the FS cache. Hence why we have the parameter. We can determine the size of the shared_buffers. The idea here is to eliminate one of those by default PostgreSQL is slow issues. Well we won't eliminate any problems unless we actually override the effective_cache_size setting by clipping it to shared_buffers. I don't really see much of a problem doing that. The only case where that would annoy someone was if they're intentionally understating effective_cache_size to push the planner into avoiding nested loops and I doin't think it's a powerful enough knob to be very likely used that way. -- greg -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] effective_cache_size less than shared_buffers
Greg, Well we won't eliminate any problems unless we actually override the effective_cache_size setting by clipping it to shared_buffers. I don't really see much of a problem doing that. The only case where that would annoy someone was if they're intentionally understating effective_cache_size to push the planner into avoiding nested loops and I doin't think it's a powerful enough knob to be very likely used that way. My experience from PostgreSQL on Windows: effective_cache_size should reflect the value of system cache from task manager. shared_buffers (on windows) should be rather small. My real-workload-tests (no benchmarks, real usage of DB-Server) showed that big shared buffers on Windows have a negative effect on PostgreSQL performance. I have found no explanation WHY it is this way. Harald -- GHUM Harald Massa persuadere et programmare Harald Armin Massa Spielberger Straße 49 70435 Stuttgart 0173/9409607 no fx, no carrier pigeon - EuroPython 2009 will take place in Birmingham - Stay tuned!
Re: [HACKERS] effective_cache_size less than shared_buffers
On Wed, 2009-02-25 at 17:21 -0600, Kevin Grittner wrote: Should we log a warning at startup when effective_cache_size is less than shared_buffers? I would say no. Although I could see an argument for the default effective_cache_size always being the same size as shared_buffers. Joshua D. Drake -Kevin -- PostgreSQL - XMPP: jdr...@jabber.postgresql.org Consulting, Development, Support, Training 503-667-4564 - http://www.commandprompt.com/ The PostgreSQL Company, serving since 1997 -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] effective_cache_size less than shared_buffers
Joshua D. Drake wrote: On Wed, 2009-02-25 at 17:21 -0600, Kevin Grittner wrote: Should we log a warning at startup when effective_cache_size is less than shared_buffers? I would say no. Although I could see an argument for the default effective_cache_size always being the same size as shared_buffers. That's certainly not what we've meant historically by ECS. Generally it's been the size of shared_buffers *and* the FS cache. If it were just the size of shared_buffers, then we wouldn't need a 2nd setting, would we? --Josh -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] effective_cache_size less than shared_buffers
On Wed, 2009-02-25 at 17:04 -0800, Josh Berkus wrote: Joshua D. Drake wrote: On Wed, 2009-02-25 at 17:21 -0600, Kevin Grittner wrote: Should we log a warning at startup when effective_cache_size is less than shared_buffers? I would say no. Although I could see an argument for the default effective_cache_size always being the same size as shared_buffers. That's certainly not what we've meant historically by ECS. Generally it's been the size of shared_buffers *and* the FS cache. If it were just the size of shared_buffers, then we wouldn't need a 2nd setting, would we? We can't determine the size of the FS cache. We can determine the size of the shared_buffers. The idea here is to eliminate one of those by default PostgreSQL is slow issues. Since we are already using X amount of shared_buffers we know we have at least X amount of cache. Sincerely, Joshua D. Drake --Josh -- PostgreSQL - XMPP: jdr...@jabber.postgresql.org Consulting, Development, Support, Training 503-667-4564 - http://www.commandprompt.com/ The PostgreSQL Company, serving since 1997 -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
