Horton

Re: POC: converting Lists into arrays

David Rowley <david.rowley@2ndquadrant.com>

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From: David Rowley <david.rowley@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Jesper Pedersen <jesper.pedersen@redhat.com>, Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-07-22T04:46:02Z
Lists: pgsql-hackers 
On Mon, 22 Jul 2019 at 16:37, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> David Rowley <david.rowley@2ndquadrant.com> writes:
> > So the bms_next_member() loop is slower when the bitmapset is fully
> > populated with all subplans, but way faster when there's just 1
> > member.
>
> Interesting.  I wonder if bms_next_member() could be made any quicker?

I had a quick look earlier and the only thing I saw was maybe to do
the first loop differently from subsequent ones.  The "w &= mask;"
does nothing useful once we're past the first bitmapword that the loop
touches.  Not sure what the could would look like exactly yet, or how
much it would help. I'll maybe experiment a bit later, but as separate
work from the other patch.

> Still, I agree that this is negligible compared to the actual work
> needed per live subplan, and the fact that the cost scales per live
> subplan is a good thing.  So no objection to this patch, but a mental
> note to take another look at bms_next_member() someday.

Thanks for having a look.  I'll have another look and will likely push
this a bit later on today if all is well.

-- 
 David Rowley                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

Commits

  1. Remove EState.es_range_table_array.

  2. Rationalize use of list_concat + list_copy combinations.

  3. Cosmetic improvements in setup of planner's per-RTE arrays.

  4. Make better use of the new List implementation in a couple of places

  5. Fix sepgsql test results for commit d97b714a2.

  6. Avoid using lcons and list_delete_first where it's easy to do so.

  7. Remove lappend_cell...() family of List functions.

  8. Clean up some ad-hoc code for sorting and de-duplicating Lists.

  9. Redesign the API for list sorting (list_qsort becomes list_sort).

  10. Remove dead code.

  11. Represent Lists as expansible arrays, not chains of cons-cells.

  12. Standardize some more loops that chase down parallel lists.

  13. Reimplement the linked list data structure used throughout the backend.