I've uploaded the latest test results to the results page at
http://community.enterprisedb.com/ldc/
The test results on the index page are not in a completely logical
order, sorry about that.
I ran a series of tests with 115 warehouses, and no surprises there. LDC
smooths the checkpoints nicely.
Another series with 150 warehouses is more interesting. At that # of
warehouses, the data disks are 100% busy according to iostat. The 90%
percentile response times are somewhat higher with LDC, though the
variability in both the baseline and LDC test runs seem to be pretty
high. Looking at the response time graphs, even with LDC there's clear
checkpoint spikes there, but they're much less severe than without.
Another series was with 90 warehouses, but without think times, driving
the system to full load. LDC seems to smooth the checkpoints very nicely
in these tests.
Heikki Linnakangas wrote:
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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