Rails/MySql consolidation of migrations

Question

I have a Rails app running over a MySql DB.

Is there a way to consolidate migrations? for example:

lets say I have a very large table called members and I create a migration to add column name to that table, later on I create another migration that adds another field address and adds index to the address field.

when i run the migration now, it will change the table 3 times: add name, add address and add index. and in each of the times, the alter table command will actually create a new table, copy all the data to it and drop the old table.

in my case, the members table is very big, over 10M records so each alter takes a few hours.

is there a way to consolidate the changes into one alter?

m_x · Accepted Answer · 2011-10-03 23:36:32Z

2

Your question is a bit difficult to understand, as you're not limited to one operation per migration.

you can easily do :

class AddNameAddressAndIndexToMembers < ActiveRecord::Migration
  def up
    change_table :members do |t|
      t.string :name
      t.text :address
      t.index :name
    end
  end

  def down
    change_table :members do |t|
      t.remove_index :name
      t.remove :name, :address
    end
  end
end

just reverse your migrations, delete previous migration files, run this migration and all should be well.

Now, if you mean that these are old migrations, it can be tricky because you don't want to reverse tons of migrations. But what do you want to achieve ? if you only need to deploy, use the current schema.rb with rake db:schema:dump and rake db:schema:load

answered Oct 3, 2011 at 23:36

m_x

12.6k7 gold badges49 silver badges60 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

mike montagne · Accepted Answer · 2012-09-10 21:32:27Z

1

If you're really wanting to maximize speed, you probably should consider deploying SQL in an execute call, in which you can for instance create a temporary result set with your desired structure, empty, drop, and/or alter the existing table, and re-populate that table from the temporary result set:

class SQLRevisions < ActiveRecord::Migration
    def change
        execute "
            [SQL PROCESS CALL]
            [SQL PROCESS CALL]
            [ETC.]"
        end
    end

Test your migration locally for the intended results, and then run it on your production instance.

answered Sep 10, 2012 at 21:32

mike montagne

1512 silver badges7 bronze badges

Collectives™ on Stack Overflow

Rails/MySql consolidation of migrations

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related