"Heikki Linnakangas" <[EMAIL PROTECTED]> writes: > I ran another series of tests, with a less aggressive bgwriter_delay setting, > which also affects the minimum rate of the writes in the WIP patch I used. > > Now that the checkpoints are spread out more, the response times are very > smooth.
So obviously the reason the results are so dramatic is that the checkpoints used to push the i/o bandwidth demand up over 100%. By spreading it out you can see in the io charts that even during the checkpoint the i/o busy rate stays just under 100% except for a few data points. If I understand it right Greg Smith's concern is that in a busier system where even *with* the load distributed checkpoint the i/o bandwidth demand during t he checkpoint was *still* being pushed over 100% then spreading out the load would only exacerbate the problem by extending the outage. To that end it seems like what would be useful is a pair of tests with and without the patch with about 10% larger warehouse size (~ 115) which would push the i/o bandwidth demand up to about that level. It might even make sense to run a test with an outright overloaded to see if the patch doesn't exacerbate the condition. Something with a warehouse size of maybe 150. I would expect it to fail the TPCC constraints either way but what would be interesting to know is whether it fails by a larger margin with the LDC behaviour or a smaller margin. Even just the fact that we're passing at 105 warehouses -- and apparently with quite a bit of headroom too -- whereas previously we were failing at that level on this hardware is a positive result as far as the TPCC benchmark methodology. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq