On Wed, Apr 29, 2020 at 2:04 PM Peter Geoghegan <p...@bowt.ie> wrote: > As a bonus, we now have an easy correctness cross-check: if some > random piece of nbtree code lands on a page (having followed a > downlink or sibling link) that is marked recycled, then clearly > something is very wrong -- throw a "can't happen" error.
If this doesn't sound that appealing to any of you, then bear this in mind: nbtree has a terrifying tendency to *not* produce wrong answers to queries when we land on a concurrently-recycled page. _bt_moveright() is willing to move right as many times as it takes to arrive at the correct page, even though in typical cases having to move right once is rare -- twice is exceptional. I suppose that there is roughly a 50% chance that we'll end up landing at a point in the key space that is to the left of the point where we're supposed to arrive at. It might take many, many page accesses before _bt_moveright() finds the correct page, but that often won't be very noticeable. Or if it is noticed, corruption won't be suspected -- we're still getting a correct answer. -- Peter Geoghegan
