Gregory Stark wrote:
"Heikki Linnakangas" <[EMAIL PROTECTED]> writes:
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.

I still don't see how spreading the writes could make things worse, but running more tests is easy. I'll schedule tests with more warehouses over the weekend.

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.

I'll do that as well, though experiences with tests like that in the past have been that it's hard to get repeatable results that way.

--
  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com

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