Re: Summary Sort workers Stats in EXPLAIN ANALYZE

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(at)vmware(dot)com>
Sent: Monday, March 21, 2022 15:50
To: pgsql-hackers(at)lists(dot)postgresql(dot)org <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Cc: Zhenghua Lyu <zlyu(at)vmware(dot)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(at)vmware(dot)com>
Sent: Monday, March 21, 2022 11:36
To: pgsql-hackers(at)lists(dot)postgresql(dot)org <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Cc: Zhenghua Lyu <zlyu(at)vmware(dot)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<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fpostgres%2Fpostgres%2Fblob%2Fd4ba8b51c76300f06cc23f4d8a41d9f7210c4866%2Fsrc%2Fbackend%2Fcommands%2Fexplain.c%23L2762&data=04%7C01%7Cgjian%40vmware.com%7C0f2c3df25e8a46bdd84f08da0aebff59%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C637834305971955895%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=RXY0uDuK7cFraHJqwU%2FQv%2BXhq3n%2F2cO6nv%2BoxHTbmCM%3D&reserved=0>

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<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fpostgres%2Fpostgres%2Fblob%2Fd4ba8b51c76300f06cc23f4d8a41d9f7210c4866%2Fsrc%2Fbackend%2Fcommands%2Fexplain.c%23L2890&data=04%7C01%7Cgjian%40vmware.com%7C0f2c3df25e8a46bdd84f08da0aebff59%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C637834305971955895%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=NotrZFufFycTmlVy3SKioUSWGzLalSu9SWCOccMXGCI%3D&reserved=0>