Rails优化mysql索引

DesignImage.from.available.audited_with_colors

# ALWAYS used

tar = DesignImage.from.available.audited_with_colors.first

> DesignImage Load (9.3ms) SELECT `design_images`.* FROM `design_images` WHERE (design_images.created_at > ('2013-3-1')) AND (design_images.imageable_id is not null and design_images.imageable_type is not null and design_images.imageable_type <> 'Inspiration' and design_images.user_id is not null) AND (edited_color = 1 and audited = 1) LIMIT 1

======================

考虑建立联合索引

检查design_images.imageable_type <> 'Inspiration'的稀疏程度

#ruby

has = {all:0, on:0, off:0}

has[:all] = DesignImage.where('design_images.created_at > "2013-03-01"').count

DesignImage.where('design_images.created_at > "2013-03-01"').find_each{|e| has[:off] = has[:off] + 1 if e.imageable_type != 'Inspiration' }

has[:on] = has[:all] - has[:off]

has

=> {:all=>132099, :on=>245, :off=>131854}

结论：

绝大部分都是imageable_type <> 'Inspiration'

建立联合索引 edited_color，audited，created_at

======================

mysql> show index from design_images;

+---------------+---------------------------------------+--------------+-----------------+-----------+-------------+------+------------+

+---------------+---------------------------------------+--------------+-----------------+-----------+-------------+------+------------+

| design_images | PRIMARY | 1 | id | A | 176810 | | BTREE |

| design_images | NewIndex1 | 1 | user_id | A | 19645 | YES | BTREE |

| design_images | NewIndex4 | 1 | is_cover | A | 176810 | YES | BTREE |

| design_images | NewIndex5 | 1 | created_at | A | 176810 | | BTREE |

| design_images | index_design_images_on_file_file_size | 1 | file_file_size | A | 176810 | YES | BTREE |

| design_images | index_design_images_on_imageable_id | 1 | imageable_id | A | 35362 | YES | BTREE |

| design_images | index_design_images_on_is_cover | 1 | is_cover | A | 176810 | YES | BTREE |

| design_images | sorts | 1 | sorts | A | 6 | YES | BTREE |

| design_images | audited | 1 | audited | A | 2 | YES | BTREE |

| design_images | edited_color | 1 | edited_color | A | 2 | YES | BTREE |

| design_images | area_id | 1 | area_id | A | 58936 | YES | BTREE |

| design_images | index_design_images_on_timestamp | 1 | created_at | A | 176810 | | BTREE |

| design_images | index_design_images_on_timestamp | 2 | file_file_name | A | 176810 | YES | BTREE |

| design_images | index_design_images_on_timestamp | 3 | file_updated_at | A | 176810 | YES | BTREE |

| design_images | index_design_images_on_imageable_type | 1 | imageable_type | A | 2996 | YES | BTREE |

| design_images | index_design_images_on_title | 1 | title | A | 44202 | YES | BTREE |

| design_images | count_index | 1 | created_at | A | 176810 | | BTREE |

| design_images | count_index | 2 | imageable_id | A | 176810 | YES | BTREE |

| design_images | count_index | 3 | imageable_type | A | 176810 | YES | BTREE |

| design_images | count_index | 4 | user_id | A | 176810 | YES | BTREE |

| design_images | count_index | 5 | edited_color | A | 176810 | YES | BTREE |

| design_images | count_index | 6 | audited | A | 176810 | YES | BTREE |

+---------------+---------------------------------------+--------------+-----------------+-----------+-------------+------+------------+

22 rows in set (0.00 sec)

add 1 => [audited, edited_color, created_at]

del 4 => count_index, audited, edited_color, index_design_images_on_timestamp

add 1 => updated_at

del 4 => index_design_images_on_file_file_size, index_design_images_on_is_cover, NewIndex4, sorts

add 1 => no_audited

db/migrate/20140716104927_remove_index_of_design_images.rb

class RemoveIndexOfDesignImages < ActiveRecord::Migration

# >show index from design_images;
#
# add 1 => [audited, edited_color, created_at]
# del 4 => count_index, audited, edited_color, index_design_images_on_timestamp
# add 1 => updated_at
# del 4 => index_design_images_on_file_file_size, index_design_images_on_is_cover, NewIndex4, sorts
# add 1 => no_audited

  def up
    remove_index :design_images, name:'count_index'
    remove_index :design_images, name:'audited'
    remove_index :design_images, name:'edited_color'
    remove_index :design_images, name:'index_design_images_on_timestamp'
    remove_index :design_images, :file_file_size
    remove_index :design_images, :is_cover
    remove_index :design_images, name:'NewIndex4'
    remove_index :design_images, name:'sorts'
    add_index :design_images, [:audited,:edited_color,:created_at], name:'from_available_audited_with_colors'
    add_index :design_images, :updated_at
    add_index :design_images, :no_audited
  end

  def down
    remove_index :design_images, name:'from_available_audited_with_colors'
    remove_index :design_images, :updated_at
    remove_index :design_images, :no_audited
    add_index :design_images, [:created_at,:imageable_id,:imageable_type,:user_id,:edited_color,:audited], name:'count_index'
    add_index :design_images, :audited, name:'audited'
    add_index :design_images, :edited_color, name:'edited_color'
    add_index :design_images, [:created_at,:file_file_name,:file_updated_at], name:'index_design_images_on_timestamp'
    add_index :design_images, :file_file_size
    add_index :design_images, :is_cover
    add_index :design_images, :is_cover, name:'NewIndex4'
    add_index :design_images, :sorts, name:'sorts'
  end
end

http://guides.rubyonrails.org/v3.2.15/migrations.html#using-the-change-method

针对有名字的索引进行删除 remove_index :design_images, name:'count_index'

remove_index方法没有在支持change的函数列表中，所以migration需要写up和down

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