Re: limiting hint bit I/O

On Tue, Jan 18, 2011 at 3:47 AM, Jim Nasby <jim(at)nasby(dot)net> wrote:
> On Jan 16, 2011, at 4:37 PM, Kevin Grittner wrote:
>> Robert Haas  wrote:
>>
>>> a quick-and-dirty attempt to limit the amount of I/O caused by hint
>>> bits. I'm still very interested in knowing what people think about
>>> that.
>>
>> I found the elimination of the response-time spike promising.  I
>> don't think I've seen enough data yet to feel comfortable endorsing
>> it, though.  I guess the question in my head is: how much of the
>> lingering performance hit was due to having to go to clog and how
>> much was due to competition with the deferred writes?  If much of it
>> is due to repeated recalculation of visibility based on clog info, I
>> think there would need to be some way to limit how many times that
>> happened before the hint bits were saved.
>
> What if we sped up the case where hint bits aren't set? Has anyone collected data on the actual pain points of checking visibility when hint bits aren't set?

I think that's worth looking into, but I don't have any present plan
to actually do it.

--
Robert Haas
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