Horton

Re: [PATCH] Push limit to sort through a subquery

Douglas Doole <dougdoole@gmail.com>

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From: Douglas Doole <dougdoole@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Konstantin Knizhnik <k.knizhnik@postgrespro.ru>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2017-08-18T20:08:28Z
Lists: pgsql-hackers

Attachments

>
> 1. The header comment for pass_down_bound() could mention "one or more
> levels of subqueries" rather than "a subquery".
>

Fixed

2. The first of the comments in the function body appears to have a
> whitespace issue that needs to be fixed manually or, better yet,
> addressed by pgindent.
>

Fixed


> 3. The formatting of the comment in the regression tests appears to be
> unlike any other comment in that same file.
>

A side effect of inheriting it from our branches ;-) Reworked.


> 4. I am pretty doubtful that "Memory: 25kB" is going to be stable
> enough for us to want that output memorialized in the regression ...
>

Fair enough. I wanted to be a bit more sophisticated in my check than
looking for a single value so I worked out something that distills the
explain down to the key elements.

Commits

  1. Propagate sort instrumentation from workers back to leader.

  2. Push tuple limits through Gather and Gather Merge.

  3. Code review for pushing LIMIT through subqueries.

  4. Make new regression test case parallel-safe, and improve its output.

  5. Push limit through subqueries to underlying sort, where possible.

  6. Move targetlist SRF handling from expression evaluation to new executor node.