An extension, that allows to log server name in sequel sharded environment. Useful for debugging, when you need to know where exactly your query is executed.

log_server_name.rb

# This extension is useful for sharded environment.
# It logs server name, for which connection is picked from pool.
# Logging happens using Database::log_info method, so be sure to set logger to database.
# The extension simply overrides original pick_server method and logs server name argument.
module Sequel
  module LogServerName
    def self.extended(db)
      pool = db.pool
      
      # check if pool is sharded
      if is_sharded? pool
        class << pool
          # override original method to log server name
          def pick_server(server)
            @db.log_info "Picking connection for server #{server}"

            super
          end  
        end

      else
        raise "LogServerName extension can only be used with sharded pool!"
      end
    end

    private

    def self.is_sharded? pool
      is_sharded_threaded?(pool) || is_sharded_single?(pool)
    end

    def self.is_sharded_threaded? pool
      defined?(ShardedThreadedConnectionPool) && pool.is_a?(ShardedThreadedConnectionPool)
    end

    def self.is_sharded_single? pool
      defined?(ShardedSingleConnectionPool) && pool.is_a?(ShardedSingleConnectionPool)
    end
  end

  Database.register_extension(:log_server_name, LogServerName)
end