On Thu, Mar 7, 2019 at 12:37 AM Peter Geoghegan <pg@bowt.ie> wrote:
> When I drew you that picture while we were in Lisbon, I mentioned to
> you that the patch sometimes used a sentinel scantid value that was
> greater than minus infinity, but less than any real scantid. This
> could be used to force an otherwise-equal-to-pivot search to go left
> rather than uselessly going right. I explained this about 30 minutes
> in, when I was drawing you a picture.
I meant the opposite: it could be used to go right, instead of going
left when descending the tree and unnecessarily moving right on the
leaf level.
As I said, moving right on the leaf level (rather than during the
descent) should only happen when it's necessary, such as when there is
a concurrent page split. It shouldn't happen reliably when searching
for the same value, unless there really are matches across multiple
leaf pages, and that's just what we have to do.
--
Peter Geoghegan
