Re: New style of hash join proposal

"Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

> Gregory Stark <stark(at)enterprisedb(dot)com> writes:
>> "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
>>> I don't understand which part of "we can do that now" isn't clear to you.
>
>> Uh, except we can't.
>
> I already demonstrated that we could. If the problem is that the
> planner is cutting over from one plan type to the other at the wrong
> rowcount because of bad cost estimates, that's a different issue
> altogether.

We seem to be talking past each other. The plan you showed is analogous but
using a plain old index scan. That means it has to look up each matching
record in a separate index scan, potentially repeatedly. A bitmap index scan
would be able to look up precisely the elements in the hash in sequential
order and precisely once.

--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com
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