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README

NOTICE: Repository moved to https://github.com/MakeYourLaws/mysql_big_table_migration

MysqlBigTableMigration
======================
                              
A Rails plugin that adds methods to ActiveRecord::Migration to allow columns 
and indexes to be added to and removed from large tables with millions of
rows in MySQL, without leaving processes seemingly stalled in state "copy
to tmp table".
                                    
For each of the standard transformations that operate on columns or indexes, 
this plugin adds a "using_tmp_table" version. These methods create a 
temporary table with the same structure as the table to be altered, applies 
the transformation to the temp table, copies data from the source table to
the temp table and then replaces the source table with the temporary one.

While it does try to ensure that data is consistent at the end of the entire 
process by locking tables and looking for rows created or modified during 
copying, this is NOT TRANSACTION SAFE as it (a) relies on timestamp columns 
and (b) doesn't handle rows that have been deleted from the source table 
after being copied to the temporary table.

Example
=======

class AddIndexOnSomeColumnToSomeTable < ActiveRecord::Migration
  def self.up
    add_index_using_tmp_table :some_table, :some_column
  end

  def self.down
    remove_index_using_tmp_table :some_table, :some_column
  end
end


Copyright (c) 2010 Mark Woods, released under the MIT license

Testing
========

You will need to bundle install dependencies for the project, as well as create a test database. To install dependencies run `bundle install`. To create the database run the following in a MySQL prompt as an admin user:

```
CREATE DATABASE mysql_big_table_migration_test;
GRANT ALL PRIVILEGES ON *.* TO 'dev'@'localhost' IDENTIFIED BY 'password';
```

After bundling dependencies, and setting up the test database, run the tests with `rake test`