On 15 April 2016 at 13:56, Tom Lane <t...@sss.pgh.pa.us> wrote: > David Rowley <david.row...@2ndquadrant.com> writes: >> On 15 April 2016 at 13:30, Andres Freund <and...@anarazel.de> wrote: >>> What'd be the point of indexing ctid, and why would it be correct? >>> Wouldn't, hm, HOT break it? > >> I don't personally see the point. > > An index on ctid is useless by definition: if you know the ctid of > a tuple, you can just go get it, never mind the index.
I'm not sure that's 100% accurate, and perhaps it's not worth arguing, as they're likely broken because of HOT anyway, but it does seem like you've totally disregarded the fact that a TIDscan does not support range scanning, where an index scan on ctid would. E.g; how many live tuples are on page 0? select count(*) from t where ctid between '(0,0)' and '(0,10000)'; I'm not saying it's going to be a common case. I just want to ensure we've considered all semi realistic use cases before we go and turn this off. -- David Rowley http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
