Re: Experimental ARC implementation

Jan Wieck wrote:

> I will follow up shortly with an approach that integrates Tom's delay
> mechanism plus my first READ_BY_VACUUM hack into one combined experiement.

Okay,

the attached patch contains the 3 already discussed and one additional
change. I also made a few changes.

1) ARC policy. Has no configurable options as it is fully self tuning.

2) vacuum_page_delay. I changed the algorithm not to do a usleep() per
page. The milliseconds usleep() now is done every vacuum_page_groupsize
pages. This makes especially sense if one can only tune in 10ms intervals.

3) Pages faulted in by VACUUM are placed onto the T1 head (LRU position)
in the ARC strategy. Thereby vacuum is even more conservative about
cache pollution than a sequential scan now.

4) A new config option lazy_checkpoint_time causes automatic timeout
controlled checkpoints (the background ones done by postmaster - and
only those) to spread out the BufferSync() over the specified amount of
seconds. This activity does not include the smgrsync() which will
actually cause the kernel to force the stuff out to disk. But it gives
the kernel time to do something already, and thereby possibly shortening
the IO burst caused by smgrsync.

I started with

vacuum_page_delay = 100
vacuum_page_groupsize = 25
checkpoint_timeout = 600
lazy_checkpoint_time = 300

and the system runs a lot smoother than before. The only not addressed
performance drop occurs now after flushing all buffers and finally
syncing during the checkpoints. And I don't have any idea how to tackle
that one.

Comments/Feedback?

Jan

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