Andres Freund <andres@anarazel.de> writes:
> On 2016-04-15 11:49:27 -0400, Tom Lane wrote:
>> I think what we should do with this is split it into two patches, one
>> to fix ALTER REPLICA IDENTITY's crash (which we'd back-patch to 9.4)
>> and one to forbid indexes on system columns (which IMO should be HEAD
>> only). The first of those should be pretty uncontroversial, so I'll
>> go ahead with pushing it --- anyone have a problem with the second?
> Only in that I'm wondering whether we shouldn't be more aggressive about
> #2.
Well, if there *is* someone out there somehow making use of an index on
one of these columns, I think we shouldn't break it in a minor release.
A more likely scenario is that someone's created such an index but it's
lying around unused. In that case, with the patch as proposed, they'd
have to drop it before they could upgrade to 9.6. That doesn't bother
me ... but again, possibly causing problems in a minor release does.
regards, tom lane