arbitrary_servers.rb

The arbitrary_servers extension allows you to connect to arbitrary servers/shards that were not defined when you created the database. To use it, you first load the extension into the Database object:

DB.extension :arbitrary_servers

Then you can pass arbitrary connection options for the server/shard to use as a hash:

DB[:table].server(host: '...', database: '...').all

Because Sequel can never be sure that the connection will be reused, arbitrary connections are disconnected as soon as the outermost block that uses them exits. So this example uses the same connection:

DB.transaction(server: {host: '...', database: '...'}) do |c|
  DB.transaction(server: {host: '...', database: '...'}) do |c2|
    # c == c2
  end
end

But this example does not:

DB.transaction(server: {host: '...', database: '...'}) do |c|
end
DB.transaction(server: {host: '...', database: '...'}) do |c2|
  # c != c2
end

You can use this extension in conjunction with the server_block extension:

DB.with_server(host: '...', database: '...') do
  DB.synchronize do
    # All of these use the host/database given to with_server
    DB[:table].insert(c: 1)
    DB[:table].update(c: 2)
    DB.tables
    DB[:table].all
  end
end

Anyone using this extension in conjunction with the server_block extension may want to do the following to so that you don’t need to call synchronize separately:

def DB.with_server(*a)
  super(*a){synchronize{yield}}
end

Note that this extension only works with the sharded threaded connection pool. If you are using the sharded single connection pool, you need to switch to the sharded threaded connection pool before using this extension.

Related module: Sequel::ArbitraryServers