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To: [email protected]
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Cc: [email protected]
Subject: RE: Improve EXPLAIN output for multicolumn B-Tree Index
Date: Wed, 26 Jun 2024 07:25:26 +0000
Message-ID: <TYWPR01MB109824F6591DC8C72F32FDDFFB1D62@TYWPR01MB10982.jpnprd01.prod.outlook.com> (raw)
In-Reply-To: <CAExHW5sZXUQDoV7VkdMGyFHtWLvkZZgfg05jxyW09jXUjtawEQ@mail.gmail.com>
References: <TYWPR01MB1098260B694D27758FE2BA46FB1C92@TYWPR01MB10982.jpnprd01.prod.outlook.com>
<CAExHW5sdpKOO+cj9=UBx_vSv=0mt2ncjJyrpdwgmbxFmWY0THg@mail.gmail.com>
<TYWPR01MB109825DAFBCA3233CA7EE77D7B1D42@TYWPR01MB10982.jpnprd01.prod.outlook.com>
<CAExHW5sZXUQDoV7VkdMGyFHtWLvkZZgfg05jxyW09jXUjtawEQ@mail.gmail.com>
>>=# EXPLAIN (VERBOSE, ANALYZE) SELECT * FROM test WHERE id1 = 1 AND id3 = 101;
>> QUERY PLAN
>>-------------------------------------------------------------------------------------------------------------------------------
>> Index Scan using test_idx on ikedamsh.test (cost=0.42..12630.10 rows=1 width=18) (actual time=0.175..279.819 rows=1 loops=1)
>> Output: id1, id2, id3, value
>> Index Cond: (test.id1 = 1) -- Change the output. Show only the bound quals.
>> Index Filter: (test.id3 = 101) -- New. Output quals which are not used as the bound quals
>> Rows Removed by Index Filter: 499999 -- New. Output when ANALYZE option is specified
>> Planning Time: 0.354 ms
>> Execution Time: 279.908 ms
>> (7 rows)
>
> I don't think we want to split these clauses. Index Cond should indicate the conditions applied
> to the index scan. Bound quals should be listed separately even though they will have an
> intersection with Index Cond. I am not sure whether Index Filter is the right name,
> maybe Index Bound Cond: But I don't know this area enough to make a final call.
OK, I understood that it's better to only add new ones. I think "Index Filter" fits other than "Index
Bound Cond" if we introduce "Rows Removed By Index Filter".
> About Rows Removed by Index Filter: it's good to provide a number when ANALYZE is
> specified, but it will be also better to specify what was estimated. We do that for (cost snd rows etc.)
> but doing that somewhere in the plan output may not have a precedent. I think we should try that
> and see what others think.
It's interesting! It’s an idea that can be applied not only to multi-column indexes, right?
I will consider the implementation and discuss it in a new thread. However, I would like to
focus on the feature to output information about multi-column indexes at first.
Regards,
--
Masahiro Ikeda
NTT DATA CORPORATION
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Subject: RE: Improve EXPLAIN output for multicolumn B-Tree Index
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