Re: Load Distributed Checkpoints test results

"Heikki Linnakangas" <heikki(at)enterprisedb(dot)com> 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