Add/Remove Indexes - Media Table

[kaysiz]

Purpose

We have an incomplete index that is causing the query to do a filesort in the filter. The first part of the query uses index to fetch record but other part is now using filesort.

=> EXPLAIN for: SELECT `media`.* FROM `media` WHERE `media`.`dataset` = 38 ORDER BY created DESC
+----+-------------+-------+------------+------+-----------------------------------+-----------------+---------+-------+------+----------+---------------------------------------+
| id | select_type | table | partitions | type | possible_keys                     | key             | key_len | ref   | rows | filtered | Extra                                 |
+----+-------------+-------+------------+------+-----------------------------------+-----------------+---------+-------+------+----------+---------------------------------------+
|  1 | SIMPLE      | media | NULL       | ref  | dataset_updated,FK62F6FE44D3D6B1B | dataset_updated | 8       | const |    1 |    100.0 | Using index condition; Using filesort |
+----+-------------+-------+------------+------+-----------------------------------+-----------------+---------+-------+------+----------+---------------------------------------+

closes: #1124

Approach

• Add a composite index that will cover both parts of the query

=> EXPLAIN for: SELECT `media`.* FROM `media` WHERE `media`.`dataset` = 38 ORDER BY created DESC
+----+-------------+-------+------------+------+---------------------------------------------------------------+-----------------------------+---------+-------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys                                                 | key                         | key_len | ref   | rows | filtered | Extra       |
+----+-------------+-------+------------+------+---------------------------------------------------------------+-----------------------------+---------+-------+------+----------+-------------+
|  1 | SIMPLE      | media | NULL       | ref  | dataset_updated,FK62F6FE44D3D6B1B,index_media_dataset_created | index_media_dataset_created | 8       | const |    1 |    100.0 | Using where |
+----+-------------+-------+------------+------+---------------------------------------------------------------+-----------------------------+---------+-------+------+----------+-------------+

• Refactor Media related queries

Open Questions and Pre-Merge TODOs

Learning

Types of changes

• Bug fix (non-breaking change which fixes an issue)

• New feature (non-breaking change which adds functionality)

• Breaking change (fix or feature that would cause existing functionality to change)

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[kaysiz]

Specifying a table name is only necessary on complex queries, simple queries like this one you can just specify the column as there is no ambiguity as to where the column belongs

[kaysiz]

This is already defined in the association has_many :media, -> { order "created DESC" }.. as a result it produces a query like this "SELECT `media`.* FROM `media` WHERE `media`.`dataset` = 38 ORDER BY created DESC, media.created DESC"