On Tue, Apr 18, 2006 at 02:12:15PM -0400, Tim Peters wrote: > [Paul Winkler] > > Interesting. Is there a recommended way now to judge whether your > > ZEO cache is "big enough"? > > Was there a recommended way before? If so, it probably sucked too ;-)
Heh. Well, I had a site that under some usage patterns would occasionally slow to a crawl with cache flips every few minutes. That was with the old default 20 MB cache size. I think I left it at 500 MB or so and that site's been fine since. But the performance demands were pretty low. > The best approach for any knob is to try different settings with your > actual app running an actual workload, measure whatever it is you're > trying to optimize, and pick the next setting to try accordingly. > Lather, rinse, repeat. Sure. But when you're in a hurry to fix a particular symptom, and the first thing you try apparently makes it go away permanently, sometimes that's good enough :-) > ZEO supports a way to create a dump file summarizing "interesting" > cache events, and there's a cache simulator program that uses that > file as input to predict how various cache statistics (like overall > hit rate) would change _if_ you had specified a different cache size. > That goes much faster than actually running the whole application > again, but the reported results are an approximation. I know several > (but not many) people have tried this post-MVCC, and the few I heard > back from said it was helpful. You can read about it in ZODB's > doc/ZEO/trace.txt. cache.txt in the same directory gives a brief > overview of the post-MVCC ZEO cache design. Thanks, those are very good documents! Out of curiosity, do you have any guesstimates on how much overhead enabling the cache trace can incur? -- Paul Winkler http://www.slinkp.com _______________________________________________ For more information about ZODB, see the ZODB Wiki: http://www.zope.org/Wikis/ZODB/ ZODB-Dev mailing list - ZODB-Dev@zope.org http://mail.zope.org/mailman/listinfo/zodb-dev
