Re: poor performance with Context Switch Storm at TPC-W.

hello.


> Do you have bgwriter on and what's the parameters? I read a theory somewhere
> that bgwriter scan a large portion of memory and cause L1/L2 thrushing, so
> with HT on, the other backends sharing the physical processor with it also
> get thrashed ... So try to turn bgwriter off or turn HT off see what's the
> difference.

bgwriter is ON.
at postgresql.conf:
> # - Background writer -
> 
> bgwriter_delay = 200            # 10-10000 milliseconds between rounds
> bgwriter_lru_percent = 1.0        # 0-100% of LRU buffers scanned/round
> bgwriter_lru_maxpages = 5        # 0-1000 buffers max written/round
> bgwriter_all_percent = 0.333        # 0-100% of all buffers scanned/round
> bgwriter_all_maxpages = 5        # 0-1000 buffers max written/round


I tried turn H/T OFF, but CSStorm occurred.
Usually, CS is about 5000.
when CSStrom occurrence, CS is about 70000.
(CS is a value smaller than the case where H/T is ON.
I think that it is because the performance of CPU fell.)


Regards
--------
Katsuhiko Okano
okano katsuhiko _at_ oss ntt co jp