Overview

This provides an API that’s relatively convenient for:

• Reading from slaves

• Using multiple shards

Usage

module MySpecProvider
  def spec_for_new
    { :adapter => 'mysql', :host => ...}
  end

  def spec_for_master shard_id
    ...
  end

  def spec_for_slave shard_id
    ...
  end
end

module MyDB
  class Widget < ActiveRecord::Base; end
  include MyStuff::MultiDB::Sharded
  extend MySpecProvider
end

MyDB.with_master_for_new do |db,spec|
  db::Widget.create(...)
end

MyDB.with_slave_for(shard_id) do |db|
  db::Widget.find(record_id);
  ...
end

Another option, if you only do primary key lookups, is to encode the shard ID into the record id.

For more, see:

• ./examples/run

• comments at top of lib/mystuff/multidb.rb

How It Works

For every spec, it defines a new sub-module of MyStuff::MultiDB, which encodes the database details, and creates new subclasses of your ActiveRecord::Base classes, within these modules. For example:

$ bin/my_stuff-multidb-unmangle MyStuff::MultiDB::MYSTUFF_MULTIDB_DB_216c6f63616c686f7374213333303621::MyDB::Widget
MyStuff::MultiDB::<localhost:3306/>::MyDB::Widget
$

There’s also lots of deep voodoo making the ActiveRecord stack use the right connection details :)

Caveats

You can not do cross-shard operations simply, eg joins.

Copying

See the COPYING file.