Horton

Re: Hybrid Hash/Nested Loop joins and caching results from subplans

David Rowley <dgrowleyml@gmail.com>

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From: David Rowley <dgrowleyml@gmail.com>
To: Andy Fan <zhihui.fan1213@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Alvaro Herrera <alvherre@alvh.no-ip.org>, Andres Freund <andres@anarazel.de>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Date: 2020-12-06T23:50:11Z
Lists: pgsql-hackers 
On Sun, 6 Dec 2020 at 03:52, Andy Fan <zhihui.fan1213@gmail.com> wrote:
>
> On Fri, Dec 4, 2020 at 10:41 PM David Rowley <dgrowleyml@gmail.com> wrote:
>>
>> I also
>> noticed that the code I'd written to build the cache lookup expression
>> included a step to deform the outer tuple. This was unnecessary and
>> slowed down the expression evaluation.
>>
>
> I thought it would be something like my 3rd suggestion on [1], however after
> I read the code,  it looked like no.  Could you explain what changes it is?
> I probably missed something.

Basically, an extra argument in ExecBuildParamSetEqual() which allows
the TupleTableSlotOps for the left and right side to be set
individually. Previously I was passing a single TupleTableSlotOps of
TTSOpsMinimalTuple.  The probeslot is a TTSOpsVirtual tuple, so
passing TTSOpsMinimalTuple causes the function to add a needless
EEOP_OUTER_FETCHSOME step to the expression.

David

Commits

  1. Add Result Cache executor node (take 2)

  2. Add Result Cache executor node

  3. Allow estimate_num_groups() to pass back further details about the estimation

  4. Allow users of simplehash.h to perform direct deletions

  5. Cache if PathTarget and RestrictInfos contain volatile functions

  6. Fix pull_varnos' miscomputation of relids set for a PlaceHolderVar.