Peter Geoghegan wrote:
> On Mon, Jun 19, 2017 at 8:36 AM, Jeff Janes <jeff.janes@gmail.com> wrote:
> > Unfortunately, it is only implemented in very narrow circumstances. You
> > have to be doing bitmap index scans of many widely scattered rows to make it
> > useful. I don't think that this is all that common of a situation. The
> > problem is that at every point in the scan, it has to be possible to know
> > what data block it is going to want N iterations in the future, so you can
> > inform the kernel to pre-fetch it. That is only easy to know for bitmap
> > scans.
>
> I think that you could prefetch in index scans by using the
> pointers/downlinks in the immediate parent page of the leaf page that
> the index scan currently pins. The sibling pointer in the leaf itself
> is no good for this, because there is only one block to prefetch
> available at a time.
Surely you could prefetch all the heap pages pointed to by index items
in the current leaf index page ...
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Álvaro Herrera https://www.2ndQuadrant.com/
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