Tom Lane wrote:
> Jan Wieck <JanWieck@Yahoo.com> writes:
>
>>What about a little hint to the buffer management that if it has to
>>evict another buffer to physically read this one (meaning the buffer
>>pool was full already) then it will not put this buffer at the top of
>>the LRU chain but rather at it's end? This way a vacuum on a large table
>>will not cause a complete cache eviction.
>
>
> I think what we really need is a way to schedule VACUUM's I/O at a lower
> priority than normal I/Os. Wouldn't be very portable :-( ... but if the
> OS offers a facility for requesting this, it'd be worth experimenting
> with.
Whatever priority it has, I think the fact that a VACUUM is kicking
everything out of a carefully populated buffer cache and possibly
replacing it with data of low to no interest at all should have some
space for improvement. And that one single optimizer mistake choosing a
seqscan over an index scan for a huge table does the same doesn't strike
me as smart either.
Jan
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