Re: Joins on TID

On Sat, 22 Dec 2018 at 16:31, Tom Lane <tgl@sss.pgh.pa.us> wrote:


> What I'm thinking about in this thread is joins on TID, which we have only
> very weak support for today --- you'll basically always wind up with a
> mergejoin, which requires full-table scan and sort of its inputs.  Still,
> that's better than a naive nestloop, and for years we've been figuring
> that that was good enough.  Several people in the other thread that
> I cited felt that that isn't good enough.  But if we think it's worth
> taking seriously, then IMO we need to add both parameterized scans (for
> nestloop-with-inner-fetch-by-tid) and hash join, because each of those
> can dominate depending on how many tuples you're joining.
>

That would certainly help if you are building a column store, or other new
index types.

-- 
Simon Riggs                http://www.2ndQuadrant.com/
<http://www.2ndquadrant.com/>
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services