Robert Haas <robertmh...@gmail.com> wrote: >> However, this is the first time I am hearing that >> battery-backed cache favors the default value. Well, it was discussed on the lists during a CommitFest. > ...if that's as bad as it gets, I'm still not sure we shouldn't > increase the default. Most people will not have their first > experience of PG on a server with a battery-backed RAID > controller, I'm thinking. And people who do have battery-backed > RAID controllers can tune the value down if need be. I have never > yet heard anyone justify why all the values in postgresql.conf > should be defined as "the lowest value that works best for at > least 1 user". > > Then again, I don't really know what I'm talking about. I think > we should be listening very carefully to people who have spent a > lot of time tuning this and taking their advice on how it should > be set by default. I'm not sure we shouldn't change the default either. There seems to be a wealth of experience showing where a bigger value can help, and a fairly narrow use case where (much to my surprise) the lower value helped. Perhaps this just fits under the "be sure to test and tune your own environment" heading, although it is a direction people might not even think to try without some hint that it can help. FWIW, we use very different configurations for bulk loading (like pg_dump piped to psql) than we do for production usage afterward. This has become part of my bag of tricks for bulk loads, but we still use a larger number after the load. Also, I haven't heard of any independent confirmation -- it could be a quirk of our hardware and configuration? Has anyone else benchmarked this to see the impact on bulk loads with BBU cache? -Kevin
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