> Should we consider this HEAD-only, or a back-patchable bug fix? > Or perhaps compromise on HEAD + 9.5?
It looks like a bug to me, but I think it might destabilize approved execution plans(*), so it may not be such a great idea to back patch branches that are already released. I think HEAD + 9.5 is good.
(*) I hear there are even applications where queries and their approved execution plans are kept in a manifest, and plans that deviate from that raise all kinds of alarms. I have never seen such a thing ...
Ugh. Anyway, do you expect any plans to change only due to avg. width estimation being different? Why would that be so?