Re: [Testperf-general] BufferSync and bgwriter

On Wed, 2004-12-15 at 00:00, Mark Wong wrote:

> http://www.osdl.org/projects/dbt2dev/results/dev4-010/211
>

Thanks Mark for turning that around so quickly. Looks good...

Results performed to compare
test 207
http://www.osdl.org/projects/dbt2dev/results/dev4-010/207

test 211 with bg3.patch which matches Neil/my option (3)
http://www.osdl.org/projects/dbt2dev/results/dev4-010/211

The overall results show 3% throughput gain. The negative effects of
checkpointing are significantly reduced and this shows up in the New
Order Transaction response time max dropping from 37s to 25s, which
looks like a significant user-visible performance gain. Similar
reduction in max response times is shown for all transaction types:
consistent removal of the longest wait times.

The gains come from greater effectiveness of the bgwriter, which reduces
I/O wait time spikes to almost zero once the shared_buffers are
completely full. (see Processor Utilization graph: wait)

It looks to me that reducing the bgwriter_delay slightly might yield
additional gains, say to 180 or 160. That should now be possible since
the cost of doing so has been greatly reduced. StrategyDirtyBufferList
has now dropped way down the list in oprofile results.

Neil very kindly points out privately that the patch has a missing
sanity check bug in it, which has shown up in Neil's testing. That
wouldn't effect these performance results, however. I leave it to Neil
to post a corrected version as a result of his efforts.

I leave it to the consensus to decide whether these results represent
significant gains and whether to add to 8.0, or defer.

Neil's suggestion (2) should also needs to be considered - test results
could still show that as the better option, so I keep an open mind.

--
Best Regards, Simon Riggs