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Paste P13595

Bad performance of mariadb optimizer
ActivePublic

Authored by jcrespo on Dec 17 2020, 7:32 PM.
root@db1133.eqiad.wmnet[mediabackups]> show create table files\G
*************************** 1. row ***************************
Table: files
Create Table: CREATE TABLE `files` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`wiki` int(10) unsigned NOT NULL,
`upload_name` varbinary(255) DEFAULT NULL,
`swift_container` int(10) unsigned DEFAULT NULL,
`swift_name` varbinary(270) DEFAULT NULL,
`file_type` tinyint(3) unsigned DEFAULT NULL,
`status` tinyint(3) unsigned DEFAULT NULL,
`sha1` varbinary(40) DEFAULT NULL,
`md5` varbinary(32) DEFAULT NULL,
`size` int(10) unsigned DEFAULT NULL,
`upload_timestamp` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
`archived_timestamp` timestamp NULL DEFAULT NULL,
`deleted_timestamp` timestamp NULL DEFAULT NULL,
`backup_status` tinyint(3) unsigned DEFAULT 1,
PRIMARY KEY (`id`), <------------------------- !!!!!!
KEY `sha1` (`sha1`),
KEY `file_type` (`file_type`),
KEY `status` (`status`),
KEY `backup_status` (`backup_status`),
KEY `wiki` (`wiki`),
KEY `swift_container` (`swift_container`),
KEY `upload_name` (`upload_name`,`status`),
KEY `upload_timestamp` (`upload_timestamp`),
CONSTRAINT `files_ibfk_1` FOREIGN KEY (`file_type`) REFERENCES `file_types` (`id`),
CONSTRAINT `files_ibfk_2` FOREIGN KEY (`status`) REFERENCES `file_status` (`id`),
CONSTRAINT `files_ibfk_3` FOREIGN KEY (`wiki`) REFERENCES `wikis` (`id`),
CONSTRAINT `files_ibfk_4` FOREIGN KEY (`backup_status`) REFERENCES `backup_status` (`id`),
CONSTRAINT `files_ibfk_5` FOREIGN KEY (`swift_container`) REFERENCES `swift_containers` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4549852 DEFAULT CHARSET=binary
1 row in set (0.001 sec)
-- simple query, just denormalize the data so it is in "human" readable form
root@db1133.eqiad.wmnet[mediabackups]> select wiki_name, upload_name, size, status_name, sha1, backup_status_name FROM files JOIN file_status ON file_status.id = files.status JOIN backup_status ON backup_status.id = files.backup_status JOIN wikis ON wikis.id = files.wiki ORDER BY files.id LIMIT 10;
<---- waiting for many minutes
^CCtrl-C -- query killed. Continuing normally.
ERROR 1317 (70100): Query execution was interrupted
root@db1133.eqiad.wmnet[mediabackups]> EXPLAIN select wiki_name, upload_name, size, status_name, sha1, backup_status_name FROM files JOIN file_status ON file_status.id = files.status JOIN backup_status ON backup_status.id = files.backup_status JOIN wikis ON wikis.id = files.wiki ORDER BY files.id LIMIT 10\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: files
type: ALL <--------------------------- WTF?????
possible_keys: status,backup_status,wiki
key: NULL
key_len: NULL
ref: NULL
rows: 4549851
Extra: Using where; Using temporary; Using filesort <---- WTF?
*************************** 2. row ***************************
id: 1
select_type: SIMPLE
table: wikis
type: eq_ref
possible_keys: PRIMARY
key: PRIMARY
key_len: 4
ref: mediabackups.files.wiki
rows: 1
Extra:
*************************** 3. row ***************************
id: 1
select_type: SIMPLE
table: backup_status
type: ALL
possible_keys: PRIMARY
key: NULL
key_len: NULL
ref: NULL
rows: 4
Extra: Using where; Using join buffer (flat, BNL join)
*************************** 4. row ***************************
id: 1
select_type: SIMPLE
table: file_status
type: eq_ref
possible_keys: PRIMARY
key: PRIMARY
key_len: 1
ref: mediabackups.files.status
rows: 1
Extra:
4 rows in set (0.001 sec)
root@db1133.eqiad.wmnet[mediabackups]> analyze table files;
+--------------------+---------+----------+-----------------------------------------+
| Table | Op | Msg_type | Msg_text |
+--------------------+---------+----------+-----------------------------------------+
| mediabackups.files | analyze | status | Engine-independent statistics collected |
| mediabackups.files | analyze | status | OK |
+--------------------+---------+----------+-----------------------------------------+
2 rows in set (54.456 sec)
root@db1133.eqiad.wmnet[mediabackups]> select wiki_name, upload_name, size, status_name, sha1, backup_status_name FROM files JOIN file_status ON file_status.id = files.status JOIN backup_status ON backup_status.id = files.backup_status JOIN wikis ON wikis.id = files.wiki ORDER BY files.id LIMIT 10;
<---- waiting for many minutes
^CCtrl-C -- query killed. Continuing normally.
ERROR 1317 (70100): Query execution was interrupted
root@db1133.eqiad.wmnet[mediabackups]> select wiki_name, upload_name, size, status_name, sha1, backup_status_name FROM files JOIN file_status ON file_status.id = files.status JOIN backup_status ON backup_status.id = files.backup_status JOIN wikis ON wikis.id = files.wiki WHERE files.id BETWEEN 1 AND 10; -- note the only change at the end
+-----------+---------------------------------------------------------+--------+-----------
| wiki_name | upload_name | size | status_nam
+-----------+---------------------------------------------------------+--------+-----------
| enwiki | !!!_(Chk_Chk_Chk)_-_One_Girl_One_Boy_cover_art.jpg | 31850 | public
| enwiki | !!!_-_!!!_album_cover.jpg | 43672 | public
| enwiki | !!!_-_Wallop.png | 118745 | public
| enwiki | !0_Trombones_Like_2_Pianos.jpg | 25319 | public
| enwiki | !ClaudiaPascoal.png | 26203 | public
| enwiki | !Haunu.ogg | 13450 | public
| enwiki | !Hero_(album).jpg | 38664 | public
| enwiki | !Women_Art_Revolution_(documentary_film)_poster_art.jpg | 15446 | public
| enwiki | !_(The_Song_Formely_Known_As)_by_Regurgitator.png | 146525 | public
| enwiki | ""Motor-Cycle"_LP_cover-Lotti_Golden.jpg | 17001 | public
+-----------+---------------------------------------------------------+--------+-----------
10 rows in set (0.001 sec)
:-(

Event Timeline

The optimizer trace reveals that for some reason, it believes it is faster to do a full scan even though if the cost is higher :(
Do you mind sending a bug to MariaDB about this? This is the optimizer trace:

root@db1133.eqiad.wmnet[mediabackups]> select * from information_schema.optimizer_trace limit 1\G
*************************** 1. row ***************************
                            QUERY: select wiki_name, upload_name, size, status_name, sha1, backup_status_name FROM files JOIN file_status ON file_status.id = files.status JOIN backup_status ON backup_status.id = files.backup_status JOIN wikis ON wikis.id = files.wiki ORDER BY files.id LIMIT 10
                            TRACE: {
  "steps": [
    {
      "join_preparation": {
        "select_id": 1,
        "steps": [
          {
            "expanded_query": "select wikis.wiki_name AS wiki_name,files.upload_name AS upload_name,files.size AS size,file_status.status_name AS status_name,files.sha1 AS sha1,backup_status.backup_status_name AS backup_status_name from (((files join file_status on(file_status.`id` = files.`status`)) join backup_status on(backup_status.`id` = files.backup_status)) join wikis on(wikis.`id` = files.wiki)) order by files.`id` limit 10"
          }
        ]
      }
    },
    {
      "join_optimization": {
        "select_id": 1,
        "steps": [
          {
            "condition_processing": {
              "condition": "WHERE",
              "original_condition": "wikis.`id` = files.wiki and backup_status.`id` = files.backup_status and file_status.`id` = files.`status`",
              "steps": [
                {
                  "transformation": "equality_propagation",
                  "resulting_condition": "multiple equal(wikis.`id`, files.wiki) and multiple equal(backup_status.`id`, files.backup_status) and multiple equal(file_status.`id`, files.`status`)"
                },
                {
                  "transformation": "constant_propagation",
                  "resulting_condition": "multiple equal(wikis.`id`, files.wiki) and multiple equal(backup_status.`id`, files.backup_status) and multiple equal(file_status.`id`, files.`status`)"
                },
                {
                  "transformation": "trivial_condition_removal",
                  "resulting_condition": "multiple equal(wikis.`id`, files.wiki) and multiple equal(backup_status.`id`, files.backup_status) and multiple equal(file_status.`id`, files.`status`)"
                }
              ]
            }
          },
          {
            "table_dependencies": [
              {
                "table": "files",
                "row_may_be_null": false,
                "map_bit": 0,
                "depends_on_map_bits": []
              },
              {
                "table": "file_status",
                "row_may_be_null": false,
                "map_bit": 1,
                "depends_on_map_bits": []
              },
              {
                "table": "backup_status",
                "row_may_be_null": false,
                "map_bit": 2,
                "depends_on_map_bits": []
              },
              {
                "table": "wikis",
                "row_may_be_null": false,
                "map_bit": 3,
                "depends_on_map_bits": []
              }
            ]
          },
          {
            "ref_optimizer_key_uses": [
              {
                "table": "files",
                "field": "status",
                "equals": "file_status.`id`",
                "null_rejecting": true
              },
              {
                "table": "files",
                "field": "backup_status",
                "equals": "backup_status.`id`",
                "null_rejecting": true
              },
              {
                "table": "files",
                "field": "wiki",
                "equals": "wikis.`id`",
                "null_rejecting": false
              },
              {
                "table": "files",
                "field": "status",
                "equals": "file_status.`id`",
                "null_rejecting": true
              },
              {
                "table": "files",
                "field": "backup_status",
                "equals": "backup_status.`id`",
                "null_rejecting": true
              },
              {
                "table": "files",
                "field": "wiki",
                "equals": "wikis.`id`",
                "null_rejecting": false
              },
              {
                "table": "file_status",
                "field": "id",
                "equals": "files.`status`",
                "null_rejecting": true
              },
              {
                "table": "file_status",
                "field": "id",
                "equals": "files.`status`",
                "null_rejecting": true
              },
              {
                "table": "backup_status",
                "field": "id",
                "equals": "files.backup_status",
                "null_rejecting": true
              },
              {
                "table": "backup_status",
                "field": "id",
                "equals": "files.backup_status",
                "null_rejecting": true
              },
              {
                "table": "wikis",
                "field": "id",
                "equals": "files.wiki",
                "null_rejecting": false
              },
              {
                "table": "wikis",
                "field": "id",
                "equals": "files.wiki",
                "null_rejecting": false
              }
            ]
          },
          {
            "rows_estimation": [
              {
                "table": "files",
                "table_scan": {
                  "rows": 4549851,
                  "cost": 46144
                }
              },
              {
                "table": "file_status",
                "table_scan": {
                  "rows": 4,
                  "cost": 1
                }
              },
              {
                "table": "backup_status",
                "table_scan": {
                  "rows": 4,
                  "cost": 1
                }
              },
              {
                "table": "wikis",
                "table_scan": {
                  "rows": 999,
                  "cost": 4
                }
              }
            ]
          },
          {
            "considered_execution_plans": [
              {
                "plan_prefix": [],
                "table": "file_status",
                "best_access_path": {
                  "considered_access_paths": [
                    {
                      "access_type": "scan",
                      "resulting_rows": 4,
                      "cost": 1,
                      "chosen": true
                    }
                  ],
                  "chosen_access_method": {
                    "type": "scan",
                    "records": 4,
                    "cost": 1,
                    "uses_join_buffering": false
                  }
                },
                "rows_for_plan": 4,
                "cost_for_plan": 1.8,
                "rest_of_plan": [
                  {
                    "plan_prefix": ["file_status"],
                    "table": "backup_status",
                    "best_access_path": {
                      "considered_access_paths": [
                        {
                          "access_type": "scan",
                          "resulting_rows": 4,
                          "cost": 1,
                          "chosen": true
                        }
                      ],
                      "chosen_access_method": {
                        "type": "scan",
                        "records": 4,
                        "cost": 1,
                        "uses_join_buffering": true
                      }
                    },
                    "rows_for_plan": 16,
                    "cost_for_plan": 6,
                    "rest_of_plan": [
                      {
                        "plan_prefix": ["file_status", "backup_status"],
                        "table": "wikis",
                        "best_access_path": {
                          "considered_access_paths": [
                            {
                              "access_type": "scan",
                              "resulting_rows": 999,
                              "cost": 4,
                              "chosen": true
                            }
                          ],
                          "chosen_access_method": {
                            "type": "scan",
                            "records": 999,
                            "cost": 4,
                            "uses_join_buffering": true
                          }
                        },
                        "rows_for_plan": 15984,
                        "cost_for_plan": 3206.8,
                        "rest_of_plan": [
                          {
                            "plan_prefix": [
                              "file_status",
                              "backup_status",
                              "wikis"
                            ],
                            "table": "files",
                            "best_access_path": {
                              "considered_access_paths": [
                                {
                                  "access_type": "ref",
                                  "index": "status",
                                  "rows": 1.52e6,
                                  "cost": 2.21e9,
                                  "chosen": true
                                },
                                {
                                  "access_type": "ref",
                                  "index": "backup_status",
                                  "rows": 2.27e6,
                                  "cost": 2.21e9,
                                  "chosen": false,
                                  "cause": "cost"
                                },
                                {
                                  "access_type": "ref",
                                  "index": "wiki",
                                  "rows": 4.55e6,
                                  "cost": 2.21e9,
                                  "chosen": false,
                                  "cause": "cost"
                                },
                                {
                                  "access_type": "scan",
                                  "resulting_rows": 4.55e6,
                                  "cost": 784448,
                                  "chosen": false
                                }
                              ],
                              "chosen_access_method": {
                                "type": "ref",
                                "records": 1.52e6,
                                "cost": 2.21e9,
                                "uses_join_buffering": false
                              }
                            },
                            "rows_for_plan": 2.4e10,
                            "cost_for_plan": 7.06e9,
                            "cost_for_sorting": 2.4e10,
                            "estimated_join_cardinality": 2.4e10
                          }
                        ]
                      },
                      {
                        "plan_prefix": ["file_status", "backup_status"],
                        "table": "files",
                        "best_access_path": {
                          "considered_access_paths": [
                            {
                              "access_type": "ref",
                              "index": "status",
                              "rows": 1.52e6,
                              "cost": 2.21e6,
                              "chosen": true
                            },
                            {
                              "access_type": "ref",
                              "index": "backup_status",
                              "rows": 2.27e6,
                              "cost": 2.21e6,
                              "chosen": false,
                              "cause": "cost"
                            },
                            {
                              "access_type": "scan",
                              "resulting_rows": 4.55e6,
                              "cost": 46144,
                              "chosen": false
                            }
                          ],
                          "chosen_access_method": {
                            "type": "ref",
                            "records": 1.52e6,
                            "cost": 2.21e6,
                            "uses_join_buffering": false
                          }
                        },
                        "rows_for_plan": 2.43e7,
                        "cost_for_plan": 7.07e6,
                        "rest_of_plan": [
                          {
                            "plan_prefix": [
                              "file_status",
                              "backup_status",
                              "files"
                            ],
                            "table": "wikis",
                            "best_access_path": {
                              "considered_access_paths": [
                                {
                                  "access_type": "eq_ref",
                                  "index": "PRIMARY",
                                  "rows": 1,
                                  "cost": 6.07e6,
                                  "chosen": true
                                },
                                {
                                  "type": "scan",
                                  "chosen": false,
                                  "cause": "cost"
                                }
                              ],
                              "chosen_access_method": {
                                "type": "eq_ref",
                                "records": 1,
                                "cost": 6.07e6,
                                "uses_join_buffering": false
                              }
                            },
                            "rows_for_plan": 2.43e7,
                            "cost_for_plan": 1.8e7,
                            "cost_for_sorting": 2.43e7,
                            "estimated_join_cardinality": 2.43e7
                          }
                        ]
                      }
                    ]
                  },
                  {
                    "plan_prefix": ["file_status"],
                    "table": "wikis",
                    "best_access_path": {
                      "considered_access_paths": [
                        {
                          "access_type": "scan",
                          "resulting_rows": 999,
                          "cost": 4,
                          "chosen": true
                        }
                      ],
                      "chosen_access_method": {
                        "type": "scan",
                        "records": 999,
                        "cost": 4,
                        "uses_join_buffering": true
                      }
                    },
                    "rows_for_plan": 3996,
                    "cost_for_plan": 805,
                    "rest_of_plan": [
                      {
                        "plan_prefix": ["file_status", "wikis"],
                        "table": "backup_status",
                        "best_access_path": {
                          "considered_access_paths": [
                            {
                              "access_type": "scan",
                              "resulting_rows": 4,
                              "cost": 3,
                              "chosen": true
                            }
                          ],
                          "chosen_access_method": {
                            "type": "scan",
                            "records": 4,
                            "cost": 3,
                            "uses_join_buffering": true
                          }
                        },
                        "rows_for_plan": 15984,
                        "cost_for_plan": 4004.8,
                        "rest_of_plan": [
                          {
                            "plan_prefix": [
                              "file_status",
                              "wikis",
                              "backup_status"
                            ],
                            "table": "files",
                            "best_access_path": {
                              "considered_access_paths": [
                                {
                                  "access_type": "ref",
                                  "index": "status",
                                  "rows": 1.52e6,
                                  "cost": 2.21e9,
                                  "chosen": true
                                },
                                {
                                  "access_type": "ref",
                                  "index": "backup_status",
                                  "rows": 2.27e6,
                                  "cost": 2.21e9,
                                  "chosen": false,
                                  "cause": "cost"
                                },
                                {
                                  "access_type": "ref",
                                  "index": "wiki",
                                  "rows": 4.55e6,
                                  "cost": 2.21e9,
                                  "chosen": false,
                                  "cause": "cost"
                                },
                                {
                                  "access_type": "scan",
                                  "resulting_rows": 4.55e6,
                                  "cost": 784448,
                                  "chosen": false
                                }
                              ],
                              "chosen_access_method": {
                                "type": "ref",
                                "records": 1.52e6,
                                "cost": 2.21e9,
                                "uses_join_buffering": false
                              }
                            },
                            "rows_for_plan": 2.4e10,
                            "cost_for_plan": 7.06e9,
                            "pruned_by_cost": true
                          }
                        ]
                      },
                      {
                        "plan_prefix": ["file_status", "wikis"],
                        "table": "files",
                        "best_access_path": {
                          "considered_access_paths": [
                            {
                              "access_type": "ref",
                              "index": "status",
                              "rows": 1.52e6,
                              "cost": 5.53e8,
                              "chosen": true
                            },
                            {
                              "access_type": "ref",
                              "index": "wiki",
                              "rows": 4.55e6,
                              "cost": 5.53e8,
                              "chosen": false,
                              "cause": "cost"
                            },
                            {
                              "access_type": "scan",
                              "resulting_rows": 4.55e6,
                              "cost": 138432,
                              "chosen": false
                            }
                          ],
                          "chosen_access_method": {
                            "type": "ref",
                            "records": 1.52e6,
                            "cost": 5.53e8,
                            "uses_join_buffering": false
                          }
                        },
                        "rows_for_plan": 6.06e9,
                        "cost_for_plan": 1.77e9,
                        "pruned_by_cost": true
                      }
                    ]
                  },
                  {
                    "plan_prefix": ["file_status"],
                    "table": "files",
                    "best_access_path": {
                      "considered_access_paths": [
                        {
                          "access_type": "ref",
                          "index": "status",
                          "rows": 1.52e6,
                          "cost": 553732,
                          "chosen": true
                        },
                        {
                          "access_type": "scan",
                          "resulting_rows": 4.55e6,
                          "cost": 46144,
                          "chosen": false
                        }
                      ],
                      "chosen_access_method": {
                        "type": "ref",
                        "records": 1.52e6,
                        "cost": 553732,
                        "uses_join_buffering": false
                      }
                    },
                    "rows_for_plan": 6.07e6,
                    "cost_for_plan": 1.77e6,
                    "rest_of_plan": [
                      {
                        "plan_prefix": ["file_status", "files"],
                        "table": "wikis",
                        "best_access_path": {
                          "considered_access_paths": [
                            {
                              "access_type": "eq_ref",
                              "index": "PRIMARY",
                              "rows": 1,
                              "cost": 6.07e6,
                              "chosen": true
                            },
                            {
                              "type": "scan",
                              "chosen": false,
                              "cause": "cost"
                            }
                          ],
                          "chosen_access_method": {
                            "type": "eq_ref",
                            "records": 1,
                            "cost": 6.07e6,
                            "uses_join_buffering": false
                          }
                        },
                        "rows_for_plan": 6.07e6,
                        "cost_for_plan": 9.05e6,
                        "rest_of_plan": [
                          {
                            "plan_prefix": ["file_status", "files", "wikis"],
                            "table": "backup_status",
                            "best_access_path": {
                              "considered_access_paths": [
                                {
                                  "access_type": "eq_ref",
                                  "index": "PRIMARY",
                                  "rows": 1,
                                  "cost": 6.07e6,
                                  "chosen": true
                                },
                                {
                                  "access_type": "scan",
                                  "resulting_rows": 4,
                                  "cost": 7892,
                                  "chosen": true
                                }
                              ],
                              "chosen_access_method": {
                                "type": "scan",
                                "records": 4,
                                "cost": 7892,
                                "uses_join_buffering": true
                              }
                            },
                            "rows_for_plan": 2.43e7,
                            "cost_for_plan": 1.39e7,
                            "cost_for_sorting": 2.43e7,
                            "estimated_join_cardinality": 2.43e7
                          }
                        ]
                      },
                      {
                        "plan_prefix": ["file_status", "files"],
                        "table": "backup_status",
                        "best_access_path": {
                          "considered_access_paths": [
                            {
                              "access_type": "eq_ref",
                              "index": "PRIMARY",
                              "rows": 1,
                              "cost": 6.07e6,
                              "chosen": true
                            },
                            {
                              "access_type": "scan",
                              "resulting_rows": 4,
                              "cost": 6388,
                              "chosen": true
                            }
                          ],
                          "chosen_access_method": {
                            "type": "scan",
                            "records": 4,
                            "cost": 6388,
                            "uses_join_buffering": true
                          }
                        },
                        "rows_for_plan": 2.43e7,
                        "cost_for_plan": 6.63e6,
                        "rest_of_plan": [
                          {
                            "plan_prefix": [
                              "file_status",
                              "files",
                              "backup_status"
                            ],
                            "table": "wikis",
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                    "uses_join_buffering": false
                  }
                },
                "rows_for_plan": 4.55e6,
                "cost_for_plan": 956114,
                "rest_of_plan": [
                  {
                    "plan_prefix": ["files"],
                    "table": "backup_status",
                    "best_access_path": {
                      "considered_access_paths": [
                        {
                          "access_type": "eq_ref",
                          "index": "PRIMARY",
                          "rows": 1,
                          "cost": 4.55e6,
                          "chosen": true
                        },
                        {
                          "access_type": "scan",
                          "resulting_rows": 4,
                          "cost": 3003,
                          "chosen": true
                        }
                      ],
                      "chosen_access_method": {
                        "type": "scan",
                        "records": 4,
                        "cost": 3003,
                        "uses_join_buffering": true
                      }
                    },
                    "rows_for_plan": 1.82e7,
                    "cost_for_plan": 4.6e6,
                    "rest_of_plan": [
                      {
                        "plan_prefix": ["files", "backup_status"],
                        "table": "wikis",
                        "best_access_path": {
                          "considered_access_paths": [
                            {
                              "access_type": "eq_ref",
                              "index": "PRIMARY",
                              "rows": 1,
                              "cost": 4.55e6,
                              "chosen": true
                            },
                            {
                              "type": "scan",
                              "chosen": false,
                              "cause": "cost"
                            }
                          ],
                          "chosen_access_method": {
                            "type": "eq_ref",
                            "records": 1,
                            "cost": 4.55e6,
                            "uses_join_buffering": false
                          }
                        },
                        "rows_for_plan": 1.82e7,
                        "cost_for_plan": 1.28e7,
                        "rest_of_plan": [
                          {
                            "plan_prefix": ["files", "backup_status", "wikis"],
                            "table": "file_status",
                            "best_access_path": {
                              "considered_access_paths": [
                                {
                                  "access_type": "eq_ref",
                                  "index": "PRIMARY",
                                  "rows": 1,
                                  "cost": 4.55e6,
                                  "chosen": true
                                },
                                {
                                  "access_type": "scan",
                                  "resulting_rows": 4,
                                  "cost": 23674,
                                  "chosen": false
                                }
                              ],
                              "chosen_access_method": {
                                "type": "eq_ref",
                                "records": 1,
                                "cost": 4.55e6,
                                "uses_join_buffering": false
                              }
                            },
                            "rows_for_plan": 1.82e7,
                            "cost_for_plan": 2.1e7,
                            "estimated_join_cardinality": 1.82e7
                          }
                        ]
                      },
                      {
                        "plan_prefix": ["files", "backup_status"],
                        "table": "file_status",
                        "best_access_path": {
                          "considered_access_paths": [
                            {
                              "access_type": "eq_ref",
                              "index": "PRIMARY",
                              "rows": 1,
                              "cost": 4.55e6,
                              "chosen": true
                            },
                            {
                              "access_type": "scan",
                              "resulting_rows": 4,
                              "cost": 19162,
                              "chosen": false
                            }
                          ],
                          "chosen_access_method": {
                            "type": "eq_ref",
                            "records": 1,
                            "cost": 4.55e6,
                            "uses_join_buffering": false
                          }
                        },
                        "rows_for_plan": 1.82e7,
                        "cost_for_plan": 1.28e7,
                        "pruned_by_heuristic": true
                      }
                    ]
                  },
                  {
                    "plan_prefix": ["files"],
                    "table": "wikis",
                    "best_access_path": {
                      "considered_access_paths": [
                        {
                          "access_type": "eq_ref",
                          "index": "PRIMARY",
                          "rows": 1,
                          "cost": 4.55e6,
                          "chosen": true
                        },
                        {
                          "type": "scan",
                          "chosen": false,
                          "cause": "cost"
                        }
                      ],
                      "chosen_access_method": {
                        "type": "eq_ref",
                        "records": 1,
                        "cost": 4.55e6,
                        "uses_join_buffering": false
                      }
                    },
                    "rows_for_plan": 4.55e6,
                    "cost_for_plan": 6.42e6,
                    "rest_of_plan": [
                      {
                        "plan_prefix": ["files", "wikis"],
                        "table": "backup_status",
                        "best_access_path": {
                          "considered_access_paths": [
                            {
                              "access_type": "eq_ref",
                              "index": "PRIMARY",
                              "rows": 1,
                              "cost": 4.55e6,
                              "chosen": true
                            },
                            {
                              "access_type": "scan",
                              "resulting_rows": 4,
                              "cost": 4131,
                              "chosen": true
                            }
                          ],
                          "chosen_access_method": {
                            "type": "scan",
                            "records": 4,
                            "cost": 4131,
                            "uses_join_buffering": true
                          }
                        },
                        "rows_for_plan": 1.82e7,
                        "cost_for_plan": 1.01e7,
                        "rest_of_plan": [
                          {
                            "plan_prefix": ["files", "wikis", "backup_status"],
                            "table": "file_status",
                            "best_access_path": {
                              "considered_access_paths": [
                                {
                                  "access_type": "eq_ref",
                                  "index": "PRIMARY",
                                  "rows": 1,
                                  "cost": 4.55e6,
                                  "chosen": true
                                },
                                {
                                  "access_type": "scan",
                                  "resulting_rows": 4,
                                  "cost": 23674,
                                  "chosen": false
                                }
                              ],
                              "chosen_access_method": {
                                "type": "eq_ref",
                                "records": 1,
                                "cost": 4.55e6,
                                "uses_join_buffering": false
                              }
                            },
                            "rows_for_plan": 1.82e7,
                            "cost_for_plan": 1.82e7,
                            "estimated_join_cardinality": 1.82e7
                          }
                        ]
                      },
                      {
                        "plan_prefix": ["files", "wikis"],
                        "table": "file_status",
                        "best_access_path": {
                          "considered_access_paths": [
                            {
                              "access_type": "eq_ref",
                              "index": "PRIMARY",
                              "rows": 1,
                              "cost": 4.55e6,
                              "chosen": true
                            },
                            {
                              "access_type": "scan",
                              "resulting_rows": 4,
                              "cost": 4131,
                              "chosen": true
                            }
                          ],
                          "chosen_access_method": {
                            "type": "scan",
                            "records": 4,
                            "cost": 4131,
                            "uses_join_buffering": true
                          }
                        },
                        "rows_for_plan": 1.82e7,
                        "cost_for_plan": 1.01e7,
                        "pruned_by_heuristic": true
                      }
                    ]
                  },
                  {
                    "plan_prefix": ["files"],
                    "table": "file_status",
                    "best_access_path": {
                      "considered_access_paths": [
                        {
                          "access_type": "eq_ref",
                          "index": "PRIMARY",
                          "rows": 1,
                          "cost": 4.55e6,
                          "chosen": true
                        },
                        {
                          "access_type": "scan",
                          "resulting_rows": 4,
                          "cost": 3003,
                          "chosen": true
                        }
                      ],
                      "chosen_access_method": {
                        "type": "scan",
                        "records": 4,
                        "cost": 3003,
                        "uses_join_buffering": true
                      }
                    },
                    "rows_for_plan": 1.82e7,
                    "cost_for_plan": 4.6e6,
                    "pruned_by_heuristic": true
                  }
                ]
              }
            ]
          },
          {
            "best_join_order": ["files", "wikis", "backup_status", "file_status"]
          },
          {
            "attaching_conditions_to_tables": {
              "original_condition": "wikis.`id` = files.wiki and backup_status.`id` = files.backup_status and file_status.`id` = files.`status`",
              "attached_conditions_computation": [
                {
                  "table": "backup_status",
                  "range_analysis": {
                    "table_scan": {
                      "rows": 4,
                      "cost": 3.9
                    },
                    "potential_range_indexes": [
                      {
                        "index": "PRIMARY",
                        "usable": true,
                        "key_parts": ["id"]
                      }
                    ],
                    "setup_range_conditions": [],
                    "group_index_range": {
                      "chosen": false,
                      "cause": "not single_table"
                    },
                    "analyzing_range_alternatives": {
                      "range_scan_alternatives": [
                        {
                          "index": "PRIMARY",
                          "chosen": false,
                          "cause": "depends on unread values"
                        }
                      ],
                      "analyzing_roworder_intersect": {
                        "cause": "too few roworder scans"
                      },
                      "analyzing_index_merge_union": []
                    }
                  }
                }
              ],
              "attached_conditions_summary": [
                {
                  "table": "files",
                  "attached": "files.`status` is not null"
                },
                {
                  "table": "wikis",
                  "attached": null
                },
                {
                  "table": "backup_status",
                  "attached": "backup_status.`id` = files.backup_status"
                },
                {
                  "table": "file_status",
                  "attached": null
                }
              ]
            }
          }
        ]
      }
    },
    {
      "join_execution": {
        "select_id": 1,
        "steps": []
      }
    }
  ]
}
MISSING_BYTES_BEYOND_MAX_MEM_SIZE: 0
          INSUFFICIENT_PRIVILEGES: 0

I am going to test the same db on MySQL/Percona for comparison first, on db2102.

root@db2102.codfw.wmnet[mediabackups]> explain select wiki_name, upload_name, size, status_name, sha1, backup_status_name FROM files JOIN file_status ON file_status.id = files.status JOIN backup_status ON backup_status.id = files.backup_status JOIN wikis ON wikis.id = files.wiki ORDER BY files.id LIMIT 10\G
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: files
   partitions: NULL
         type: index
possible_keys: status,backup_status,wiki
          key: PRIMARY <------------------------------------- preferred index
      key_len: 4
          ref: NULL
         rows: 10
     filtered: 100.00
        Extra: Using where <------------------------------------ no filesort
*************************** 2. row ***************************
           id: 1
  select_type: SIMPLE
        table: file_status
   partitions: NULL
         type: eq_ref
possible_keys: PRIMARY
          key: PRIMARY
      key_len: 1
          ref: mediabackups.files.status
         rows: 1
     filtered: 100.00
        Extra: NULL
*************************** 3. row ***************************
           id: 1
  select_type: SIMPLE
        table: backup_status
   partitions: NULL
         type: eq_ref
possible_keys: PRIMARY
          key: PRIMARY
      key_len: 1
          ref: mediabackups.files.backup_status
         rows: 1
     filtered: 100.00
        Extra: NULL
*************************** 4. row ***************************
           id: 1
  select_type: SIMPLE
        table: wikis
   partitions: NULL
         type: eq_ref
possible_keys: PRIMARY
          key: PRIMARY
      key_len: 4
          ref: mediabackups.files.wiki
         rows: 1
     filtered: 100.00
        Extra: NULL
4 rows in set, 1 warning (0.035 sec)

root@db2102.codfw.wmnet[mediabackups]> show warnings;
+-------+------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Level | Code | Message                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
+-------+------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Note  | 1003 | /* select#1 */ select `mediabackups`.`wikis`.`wiki_name` AS `wiki_name`,`mediabackups`.`files`.`upload_name` AS `upload_name`,`mediabackups`.`files`.`size` AS `size`,`mediabackups`.`file_status`.`status_name` AS `status_name`,`mediabackups`.`files`.`sha1` AS `sha1`,`mediabackups`.`backup_status`.`backup_status_name` AS `backup_status_name` from `mediabackups`.`files` join `mediabackups`.`file_status` join `mediabackups`.`backup_status` join `mediabackups`.`wikis` where ((`mediabackups`.`file_status`.`id` = `mediabackups`.`files`.`status`) and (`mediabackups`.`backup_status`.`id` = `mediabackups`.`files`.`backup_status`) and (`mediabackups`.`wikis`.`id` = `mediabackups`.`files`.`wiki`)) order by `mediabackups`.`files`.`id` limit 10 |
+-------+------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.034 sec)

root@db2102.codfw.wmnet[mediabackups]> select wiki_name, upload_name, size, status_name, sha1, backup_status_name FROM files JOIN file_status ON file_status.id = files.status JOIN backup_status ON backup_status.id = files.backup_status JOIN wikis ON wikis.id = files.wiki ORDER BY files.id LIMIT 10;
+-----------+---------------------------------------------------------+--------+-------------+------------------------------------------+--------------------+
| wiki_name | upload_name                                             | size   | status_name | sha1                                     | backup_status_name |
+-----------+---------------------------------------------------------+--------+-------------+------------------------------------------+--------------------+
| enwiki    | !!!_(Chk_Chk_Chk)_-_One_Girl_One_Boy_cover_art.jpg      |  31850 | public      | 2c5f4c5ff0e57ffcea85c1da92b4599336d75fb9 | backedup           |
| enwiki    | !!!_-_!!!_album_cover.jpg                               |  43672 | public      | 25c046a856d14314cda3c741539f41fbc6c63fe2 | backedup           |
| enwiki    | !!!_-_Wallop.png                                        | 118745 | public      | 3fccf40bfd27ccfac1d057198fd4315afd50b42d | backedup           |
| enwiki    | !0_Trombones_Like_2_Pianos.jpg                          |  25319 | public      | 3ec8b40e128ad8c677b869ef9280104c03bff2e5 | backedup           |
| enwiki    | !ClaudiaPascoal.png                                     |  26203 | public      | 66a8f68f1ac4708aaa600dcc5a5690836868a2c9 | backedup           |
| enwiki    | !Haunu.ogg                                              |  13450 | public      | 77577544869768e619829c4e9e6e0ddde94f9421 | backedup           |
| enwiki    | !Hero_(album).jpg                                       |  38664 | public      | c42574f1639e0bd96749f0ac3e76b69573ce2ba3 | backedup           |
| enwiki    | !Women_Art_Revolution_(documentary_film)_poster_art.jpg |  15446 | public      | fd33557daf97103c72401e7a33723360cd0db9f4 | backedup           |
| enwiki    | !_(The_Song_Formely_Known_As)_by_Regurgitator.png       | 146525 | public      | c491daf7642bfa1d192b22bc83cc41c721d1092e | backedup           |
| enwiki    | ""Motor-Cycle"_LP_cover-Lotti_Golden.jpg                |  17001 | public      | dbc8dcac96e647d0dfcba702c88e86a0935e2d88 | backedup           |
+-----------+---------------------------------------------------------+--------+-------------+------------------------------------------+--------------------+
10 rows in set (0.035 sec)
jcrespo changed the title of this paste from Terrible mariadb optimizer (FYI) to Bad performance of mariadb optimizer.Dec 18 2020, 9:21 AM