From: | Andres Freund <andres(at)anarazel(dot)de> |
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To: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Disallow unique index on system columns |
Date: | 2016-04-15 01:30:24 |
Message-ID: | 20160415013024.msdqhq4zr3jlylxt@alap3.anarazel.de |
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Lists: | pgsql-hackers |
On 2016-04-15 13:26:35 +1200, David Rowley wrote:
> 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.
What'd be the point of indexing ctid, and why would it be correct?
Wouldn't, hm, HOT break it?
Andres
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