Re: [PATCH] Add extra statistics to explain for Nested Loop
От | Tomas Vondra |
---|---|
Тема | Re: [PATCH] Add extra statistics to explain for Nested Loop |
Дата | |
Msg-id | 20201031012053.arjh7eehmlzud45p@development обсуждение исходный текст |
Ответ на | Re: [PATCH] Add extra statistics to explain for Nested Loop (e.sokolova@postgrespro.ru) |
Ответы |
Re: [PATCH] Add extra statistics to explain for Nested Loop
Re: [PATCH] Add extra statistics to explain for Nested Loop |
Список | pgsql-hackers |
Hello Ekaterina, seems like an interesting and useful improvement. I did a quick review of the patch - attached is a 0002 patch with a couple minor changes (the 0001 is just your v1 patch, to keep cfbot happy). 1) There's a couple changes to follow project code style (e.g. brackets after "if" on a separate line, no brackets around single-line blocks, etc.). I've reverted some unnecessary whitespace changes. Minor stuff. 2) I don't think InstrEndLoop needs to check if min_t == 0 before initializing it in the first loop. It certainly has to be 0, no? Same for min_tuples. I also suggest comment explaining that we don't have to initialize the max values. 3) In ExplainNode, in the part processing per-worker stats, I think some of the fields are incorrectly referencing planstate->instrument instead of using the 'instrument' variable from WorkerInstrumentation. In general, I agree with Andres this might add overhead to explain analyze, although I doubt it's going to be measurable. But maybe try doing some measurements for common and worst-cases. I wonder if we should have another option EXPLAIN option enabling this. I.e. by default we'd not collect/print this, and users would have to pass some option to EXPLAIN. Or maybe we could tie this to VERBOSE? Also, why print this only for nested loop, and not for all nodes with (nloops > 1)? I see there was some discussion why checking nodeTag is necessary to identify NL, but that's not my point. regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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