Peter Geoghegan wrote: > On Mon, Jun 19, 2017 at 8:36 AM, Jeff Janes <jeff.ja...@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 ... -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
