> On 11/14/11 02:17, Vlad Khorsun wrote:
>> I thought about to change cache_writer in this direction - make it to do
>> "mini-flush"
>> instead of writting one page at time. But, note, we have no cache_writer
>> thread in CS\SC
>> and we can do a little (almost nothing) when page lock is downgraded (often
>> case in CS, i
>> think).
>>
>
> What prevents us from adding cache writer to classic?
Cache writer is useful for large cache. It adds almost none or even could
drop
performance for small cache (which is typical for CS). Small cache often
overfilled
during one operation and dirty pages written as result of preemption by new
pages.
Technically we can enable cache writer for CS but i doubt it is good idea and
i'm
afraid to add more threads per process on Linux.
>> I don't think that writting more than one dirty page when free buffer is
>> needed is good
>> idea as it could delay user process significantly. I could be wrong...
>>
>
> Worth checking...
> Remember how changing FW affects tpc/c performance on small database?
It was expected :)
My doubt is that we will write more pages than necessary. Imagine small
cache (CS)
and set of actively modifying pages. Currently we will write them one-by-one
when new
buffer is required. You offer to write, say, 2 pages at time and replace one of
them.
Second written page could be modified again and we will write it again, so
first write
was not needed.
Regards,
Vlad
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