mysql_double_index

MysqlDoubleIndex

Welcome to your new gem! In this directory, you'll find the files you need to be able to package up your Ruby library into a gem. Put your Ruby code in the file lib/mysql_double_index. To experiment with that code, run bin/console for an interactive prompt.

TODO: Delete this and the text above, and describe your gem

Doc

冗余和重复索引的概念：

MySQL允许在相同列上创建多个索引，无论是有意的还是无意的。MySQL需要单独维护重复的索引，并且优化器在优化查询的时候也需要逐个地进行考虑，这会影响性能。

重复索引：是指在相同的列上按照相同的顺序创建的相同类型的索引。应该避免这样创建重复索引，发现后也应该立即移除。

冗余索引：冗余索引和重复索引有一些不同，如果创建了索引(A,B)，再创建索引(A)就是冗余索引，因为这只是前一个索引的前缀索引。因此索引(A,B)也可以当索引(A)来使用(这种冗余只是对B-Tree索引来说)。冗余索引通常发生在为表添加新索引的时候。例如，有人可能会增加一个新的索引(A,B)而不是扩展已有的索引(A)。还有一种情况是将一个索引扩展为(A,ID)，其中ID是主键，对于InnoDB来说主键列已经包含在二级索引中了，索引也是冗余的。

大多数的情况下都不需要冗余索引，应该尽量扩展已有的索引而不是创建新索引。但也有时候出于性能方面的考虑需要冗余索引，因为扩展已有的索引会导致其变得太大，从而影响其它使用该索引的查询的性能。

Installation

Add this line to your application's Gemfile:

gem 'mysql_double_index'

And then execute:

$ bundle

Or install it yourself as:

$ gem install mysql_double_index

Usage

And then execute:

$ rails c

#查询单个表重复&冗余索引
$ > MysqlDoubleIndex.db_double_index("articles")

#查询所有表重复&冗余索引
$ > MysqlDoubleIndex.db_double_index

#查询单个表磁盘占用大小
$ > MysqlDoubleIndex.db_table_size("articles")

#查询所有表磁盘占用大小
$ > MysqlDoubleIndex.db_table_size

Development

After checking out the repo, run bin/setup to install dependencies. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/mysql_double_index. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

The gem is available as open source under the terms of the MIT License.