Re: Experimental ARC implementation

Greg Stark wrote:
>
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
>
> > Have you considered having the background writer check the pages it is
> > about to write to see if they can be added to the FSM, thereby reducing
> > the need for vacuum? Seems we would need to add a statistics parameter
> > so pg_autovacuum would know how many tuples the background write added
> > to the freespace map, so it doesn't vacuum a table that doesn't need it.
>
> This would suffer from the previously mentioned problem of having to pull in
> index pages and dirty them when it's trying to flush and clean pages.

I am confused why the index would be involved in this.

> Conceivably it could just count up the dead tuples and provide that
> information to something like pg_autovacuum so it knows when it's time to run
> a vacuum. I don't see that as all that much of a win over the current
> heuristics. At best it means a big batch update will trigger a vacuum sooner
> so you don't have to manually run vacuum to avoid overflowing the fsm.

Yea, probably. Another idea would be for tuple reuse to favor pages
already in the cache so it doesn't have to read in a page from disk.

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