On Wed, 5 Sep 2007, Josh Berkus wrote:

Are you talking about 200 runs with 8.2.4 or 8.3?
8.2.4.


Right, then we're in agreement here. I did something like 4000 small test runs with dozens of settings under various 8.2.X releases and my conclusion was that in the general case, it just didn't work at reducing checkpoint spikes the way it was supposed to. Your statement that you never found a "set of bgwriter settings we'd happily recommend to others" was also the case for me.

While there certainly are some cases where we've heard about people whose workloads were such that the background writer worked successfully for them, I consider those lucky rather than normal. I'd like those people to test 8.3 because I'd hate to see the changes made to improve the general case cause a regression for them.

You are certainly spot-on that this causes a bit of a problem for testing 8.3 in beta, because if you come from a world-view where the 8.2.4 background writer was never successful it's hard to figure out a starting point for comparing it to the one in 8.3. Maybe I'll spark some ideas when I get the rest of my data out here soon.

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* Greg Smith [EMAIL PROTECTED] http://www.gregsmith.com Baltimore, MD

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