Re: wal_buffers, redux

On Wed, Mar 14, 2012 at 7:20 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Tue, Mar 13, 2012 at 3:48 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> On Mon, Mar 12, 2012 at 4:45 PM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
>>> Rerunning all 4 benchmarks (both 16MB and 32MB wal_buffers on both
>>> machines) with fsync=off (as well as synchronous_commit=off still)
>>> might help clarify things.
>>
>> I reran the 32-client benchmark on the IBM machine with fsync=off and got this:
>>
>> 32MB: tps = 26809.442903 (including connections establishing)
>> 16MB: tps = 26651.320145 (including connections establishing)
>>
>> That's a speedup of nearly a factor of two, so clearly fsync-related
>> stalls are a big problem here, even with wal_buffers cranked up
>> through the ceiling.
>
> And here's a tps plot with wal_buffers = 16MB, fsync = off.  The
> performance still bounces up and down, so there's obviously some other
> factor contributing to latency spikes

Initialization of WAL file? Do the latency spikes disappear if you start
benchmark after you prepare lots of the recycled WAL files?

Regards,

--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center