Re: Improvement of checkpoint IO scheduler for stable transaction responses

Hi,

I took results of my separate patches and original PG.

* Result of DBT-2      | TPS      90%tile    Average  Maximum
------------------------------------------------------
original_0.7  | 3474.62  18.348328  5.739    36.977713
original_1.0  | 3469.03  18.637865  5.842    41.754421
fsync         | 3525.03  13.872711  5.382    28.062947
write         | 3465.96  19.653667  5.804    40.664066
fsync + write | 3564.94  16.31922   5.1      34.530766
 - 'original_*' indicates checkpoint_completion_target in PG 9.2.4. - In other patched postgres,
checkpoint_completion_targetsets 0.7. - 'write' is applied write patch, and 'fsync' is applied fsync patch. - 'fsync +
write'is applied both patches.
 


* Investigation of result - Large value of checkpoint_completion_target in original and the patch in 
write become slow latency in benchmark transactions. Because slow write pages are 
caused long time fsync IO in final checkpoint. - The patch in fsync has an effect latency in each file fsync. Continued

fsyncsin each files are caused slow latency. Therefore, it is good for latency 
that fsync stage in checkpoint has sleeping time after slow fsync IO. - The patches of fsync + write were seemed to
improveTPS. I think that write 
 
patch does not disturb transactions which are in full-page-write WAL write than 
original(plain) PG.

I will send you more detail investigation and result next week. And I will also 
take result in pgbench. If you mind other part of benchmark result or parameter 
of postgres, please tell me.

Best Regards,
--
Mitsumasa KONDO
NTT Open Source Software Center