Horton

HashAgg's batching counter starts at 0, but Hash's starts at 1.

David Rowley <dgrowleyml@gmail.com>

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From: David Rowley <dgrowleyml@gmail.com>
To: PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>, Jeff Davis <pgsql@j-davis.com>
Date: 2020-07-01T02:03:46Z
Lists: pgsql-hackers 
Hi,

While working on 40efbf870 I noticed that when performing a Hash Join
that we always start out by setting nbatch to 1.  That seems
reasonable as it's hard to imagine being able to complete any non-zero
amount of work in fewer than 1 batch.

In the HashAgg case, since 40efbf870, we'll display:

"HashAgg Batches": 0,

if you do something like: explain(analyze, format json) select
distinct oid from pg_class;

I'd rather this said that the number of batches was 1.

Does anyone have any objections to that being changed?

David

Commits

  1. Make EXPLAIN ANALYZE of HashAgg more similar to Hash Join

  2. Further adjustments to Hashagg EXPLAIN ANALYZE output

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

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

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