Discovered as part of MDEV-9420. See these comments:
https://mariadb.atlassian.net/browse/MDEV-9420?focusedCommentId=80164&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-80164
https://mariadb.atlassian.net/browse/MDEV-9420?focusedCommentId=80165&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-80165
Copying here:
Checking problem #1.
MariaDB 10.0:
MariaDB [j10]> explain select * from point_activite
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WHERE `id_activity_list` = 1479 AND `id_contact_Script` = 2075347 AND `id_contact_campaign_pass` = 1920183 \G
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*************************** 1. row ***************************
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id: 1
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select_type: SIMPLE
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table: point_activite
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type: index_merge
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possible_keys: id_contact_Script,id_activity_list,id_contact_campaign_pass
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key: id_contact_campaign_pass,id_contact_Script
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key_len: 9,9
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ref: NULL
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rows: 1
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Extra: Using intersect(id_contact_campaign_pass,id_contact_Script); Using where
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MariaDB [j10]> explain select * from point_activite
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WHERE `id_activity_list` = 1479 AND `id_contact_Script` = 2075347 AND `id_contact_campaign_pass` = 1920183
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ORDER BY `IDPoint_Activite`\G
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*************************** 1. row ***************************
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id: 1
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select_type: SIMPLE
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table: point_activite
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type: index_merge
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possible_keys: id_contact_Script,id_activity_list,id_contact_campaign_pass
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key: id_contact_campaign_pass,id_contact_Script
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key_len: 9,9
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ref: NULL
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rows: 1
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Extra: Using intersect(id_contact_campaign_pass,id_contact_Script); Using where; Using filesort
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So, in 10.0, the plan is always to use index_merge to produce one row. Actually, two rows are produced and the query finishes in 0.05 sec or less.
In 10.1.10:
MariaDB [j10]> explain select * from point_activite
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WHERE `id_activity_list` = 1479 AND `id_contact_Script` = 2075347 AND `id_contact_campaign_pass` = 1920183\G
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*************************** 1. row ***************************
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id: 1
|
select_type: SIMPLE
|
table: point_activite
|
type: index_merge
|
possible_keys: id_contact_Script,id_activity_list,id_contact_campaign_pass
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key: id_contact_campaign_pass,id_contact_Script
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key_len: 9,9
|
ref: NULL
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rows: 1
|
Extra: Using intersect(id_contact_campaign_pass,id_contact_Script); Using where
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The same so far. Adding ORDER BY:
explain select * from point_activite
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WHERE `id_activity_list` = 1479 AND `id_contact_Script` = 2075347 AND `id_contact_campaign_pass` = 1920183
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ORDER BY `IDPoint_Activite`\G
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*************************** 1. row ***************************
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id: 1
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select_type: SIMPLE
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table: point_activite
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type: index
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possible_keys: id_contact_Script,id_activity_list,id_contact_campaign_pass
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key: PRIMARY
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key_len: 8
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ref: NULL
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rows: 1997722
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Extra: Using where
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And the plan becomes much worse. It wants to read nearly 2M rows. Execution takes 1 min 39 sec.
Sergei Petrunia
made changes -
| Field |
Original Value |
New Value |
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Component/s
|
|
Optimizer
[ 10200
]
|
Sergei Petrunia
made changes -
|
Labels
|
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order-by-optimization regression
|
Sergei Petrunia
made changes -
|
Labels
|
order-by-optimization regression
|
optimizer order-by-optimization regression
|
Sergei Petrunia
made changes -
|
Fix Version/s
|
|
10.1.11
[ 21202
]
|
|
Resolution
|
|
Fixed
[ 1
]
|
|
Status
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Open
[ 1
]
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Closed
[ 6
]
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Sergei Petrunia
made changes -
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Affects Version/s
|
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10.1.10
[ 20402
]
|
|
Affects Version/s
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10.1
[ 16100
]
|
|
Sergei Golubchik
made changes -
|
Workflow
|
MariaDB v3
[ 73737
]
|
MariaDB v4
[ 150030
]
|
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Bug
Major