Re: Disallow unique index on system columns

On 15 April 2016 at 13:02, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> writes:
>> I proposed a fix over there, but it didn't go anywhere, probably
>> because Tom and Andres discussed just disallowing unique indexes on
>> system columns altogether. So, the attached patch does just that, and
>> also fixes up the replica identity bugs too, as it's still possible
>> that someone could create a unique index on a system column with an
>> old version, upgrade, then try to set the replica identity to that
>> index. We'd need to handle that correctly, so I fixed that too.
>
> AFAIR, what we were discussing was disallowing any index on a system
> column (other than OID). I do not see why only unique indexes are
> problematic for them; the semantic issues are independent of that.

I have to admit that my thoughts only considered ctid, which I
imagined would have been OK to have an index on. As for the other
system columns (apart from OID), I agree.

--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services