Re: Summary Sort workers Stats in EXPLAIN ANALYZE

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От Jian Guo
Тема Re: Summary Sort workers Stats in EXPLAIN ANALYZE
Дата
Msg-id SN6PR05MB519978F0435079207762C54EC4199@SN6PR05MB5199.namprd05.prod.outlook.com
обсуждение исходный текст
Ответ на Re: Summary Sort workers Stats in EXPLAIN ANALYZE  (Jian Guo <gjian@vmware.com>)
Ответы Re: Summary Sort workers Stats in EXPLAIN ANALYZE  (Julien Rouhaud <rjuju123@gmail.com>)
Список pgsql-hackers
Дерево обсуждения
For a simple demo, with this explain statement：

-- Test sort stats summary
set force_parallel_mode=on;
select explain_filter('explain (analyze, summary off, timing off, costs off, format json) select * from tenk1 order by unique1');

Before this patch, we got plan like this:


           "Node Type": "Sort",                +
           "Parent Relationship": "Outer",     +
           "Parallel Aware": false,            +
           "Async Capable": false,             +
           "Actual Rows": 10000,               +
           "Actual Loops": 1,                  +
           "Sort Key": ["unique1"],            +
           "Workers": [                        +
             {                                 +
               "Worker Number": 0,             +
               "Sort Method": "external merge",+
               "Sort Space Used": 2496,        +
               "Sort Space Type": "Disk"       +
             }                                 +
           ],                                  +



After this patch, the effected plan is this:

           "Node Type": "Sort",               +
           "Parent Relationship": "Outer",    +
           "Parallel Aware": false,           +
           "Async Capable": false,            +
           "Actual Rows": N,                  +
           "Actual Loops": N,                 +
           "Sort Key": ["unique1"],           +
           "Workers planned": N,              +
           "Sort Method": "external merge",   +
           "Average Sort Space Used": N,      +
           "Peak Sort Space Used": N,         +
           "Sort Space Type": "Disk",         +
From: Jian Guo <gjian@vmware.com>
Sent: Monday, March 21, 2022 15:50
To: pgsql-hackers@lists.postgresql.org <pgsql-hackers@lists.postgresql.org>
Cc: Zhenghua Lyu <zlyu@vmware.com>
Subject: Re: Summary Sort workers Stats in EXPLAIN ANALYZE
 
There is some problem with the last patch, I have removed the `ExplainOpenWorker` call to fix.

And also, I have added a test case in explain.sql​ according to the code change.
From: Jian Guo <gjian@vmware.com>
Sent: Monday, March 21, 2022 11:36
To: pgsql-hackers@lists.postgresql.org <pgsql-hackers@lists.postgresql.org>
Cc: Zhenghua Lyu <zlyu@vmware.com>
Subject: Summary Sort workers Stats in EXPLAIN ANALYZE
 

In current EXPLAIN ANALYZE implementation, the Sort Node stats from each workers are not summarized: https://github.com/postgres/postgres/blob/d4ba8b51c76300f06cc23f4d8a41d9f7210c4866/src/backend/commands/explain.c#L2762

When the worker number is large, it will print out huge amount of node details in the plan. I have created this patch to summarize the tuplesort stats by AverageSpaceUsed / PeakSpaceUsed, make it behave just like in `show_incremental_sort_group_info()`: https://github.com/postgres/postgres/blob/d4ba8b51c76300f06cc23f4d8a41d9f7210c4866/src/backend/commands/explain.c#L2890

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