Horton

Re: [PATCH] Incremental sort (was: PoC: Partial sort)

Alvaro Herrera <alvherre@2ndquadrant.com>

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From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: James Coleman <jtc331@gmail.com>
Cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>, Michael Paquier <michael@paquier.xyz>, Rafia Sabih <rafia.pghackers@gmail.com>, Peter Geoghegan <pg@bowt.ie>, Simon Riggs <simon@2ndquadrant.com>, Shaun Thomas <shaun.thomas@2ndquadrant.com>, Dmitry Dolgov <9erthalion6@gmail.com>, Alexander Korotkov <a.korotkov@postgrespro.ru>, Tom Lane <tgl@sss.pgh.pa.us>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>, andreas@proxel.se
Date: 2020-03-23T16:44:46Z
Lists: pgsql-hackers 
On 2020-Mar-22, James Coleman wrote:

> One question I have while I work on that: I've noticed some confusion
> in the patch as to whether we should refer to the node below the
> incremental sort node in the plan tree (i.e., the node we get tuples
> from) as the inner node or the outer node. Intuitively I'd expect to
> call it the inner node, but the original patch referred to it
> frequently as the outer node. The outerPlanState/innerPlanState macro
> comments don't offer a lot of clarification though they're "to avoid
> confusion" about right/left inner/outer. I suppose if the
> outerPlanState macro is working here the correct term should be outer?

I think the inner/outer distinction comes from join nodes wanting to
distinguish which child drives the scan of the other.  If there's a
single child, there's no need to make such a distinction: it's just "the
child".  And if it's the only child, conventionally we use the first
one, which conventionally is (for us westerners) the one on the left.
This view is supported by the fact that outerPlanState() appears 113
times in the code whereas innerPlanState() appears only 27 times --
that is, all plan types that use only one child use the outer one.  They
could use either, as long as it does that consistently, I think.

Therefore the term should be "outer".  It's not "outer" to the parent
incremental sort; it's just the "outer" of its two possible children.

I think.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Commits

  1. Further adjustments to Hashagg EXPLAIN ANALYZE output

  2. Rework EXPLAIN format for incremental sort

  3. Fix typos and improve incremental sort comments

  4. Stabilize incremental_sort tests

  5. Minor improvements in Incremental Sort explain

  6. Consider Incremental Sort paths at additional places

  7. Fix representation of SORT_TYPE_STILL_IN_PROGRESS.

  8. Fix failures in incremental_sort due to number of workers

  9. Fix show_incremental_sort_info with force_parallel_mode

  10. Implement Incremental Sort

  11. Fix handling of "Subplans Removed" field in EXPLAIN output.

  12. Fix EXPLAIN (SETTINGS) to follow policy about when to print empty fields.

  13. Ensure plpgsql result tuples have the right composite type marking.

  14. Propagate sort instrumentation from workers back to leader.

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

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

  17. Fix inappropriate printing of never-measured times in EXPLAIN.

  18. Fix some infelicities in EXPLAIN output for parallel query plans.