Greg Stark <gsstark(at)mit(dot)edu> writes:
> Mark Wong <markw(at)osdl(dot)org> writes:
>> I have some initial results using 8.0beta5 with our OLTP workload.
>> throughput: 4076.97
> Do people really only look at the "throughput" numbers? Looking at those
> graphs it seems that while most of the OLTP transactions are fulfilled in
> subpar response times, there are still significant numbers that take as much
> as 30s to fulfil.
> Is this just a consequence of the type of queries being tested and the data
> distribution? Or is Postgres handling queries that could run consistently fast
> but for some reason generating large latencies sometimes?
Given the regular shape of the first graph (transactions/minute),
there's every reason to think that the slowdowns are caused by
checkpoint I/O storms. It would be worth the trouble to experiment
with adjusting the bgwriter parameters to even out the flow of write
operations. (I think I've already pointed out that the current defaults
for the bgwriter seem mighty conservative.)
regards, tom lane
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