diff --git a/bin/standard_benchmark b/bin/standard_benchmark
index 410135a..a977da9 100755
--- a/bin/standard_benchmark
+++ b/bin/standard_benchmark
@@ -64,11 +64,11 @@ def benchmark(str, n, coll_name, data, create_index=false)
   coll.create_index('x') if create_index
   profile(str) do
     times = []
-    GC.start
-    t1 = Time.now
-      n.times { |i| yield(coll, i) }
-    t2 = Time.now
-    times << t2 - t1
+      GC.start
+      t1 = Time.now
+        n.times { |i| yield(coll, i) }
+      t2 = Time.now
+      times << t2 - t1
     report(str, times.min)
   end
 end
diff --git a/lib/mongo.rb b/lib/mongo.rb
index 787de49..f2a65e0 100644
--- a/lib/mongo.rb
+++ b/lib/mongo.rb
@@ -31,5 +31,5 @@ module Mongo
   ASCENDING = 1
   DESCENDING = -1
 
-  VERSION = "0.17.2"
+  VERSION = "0.18"
 end
diff --git a/lib/mongo/admin.rb b/lib/mongo/admin.rb
index 5141efa..66e6f63 100644
--- a/lib/mongo/admin.rb
+++ b/lib/mongo/admin.rb
@@ -30,7 +30,7 @@ module Mongo
     def profiling_level
       oh = OrderedHash.new
       oh[:profile] = -1
-      doc = @db.db_command(oh)
+      doc = @db.command(oh)
       raise "Error with profile command: #{doc.inspect}" unless @db.ok?(doc) && doc['was'].kind_of?(Numeric)
       case doc['was'].to_i
       when 0
@@ -57,7 +57,7 @@ module Mongo
                      else
                        raise "Error: illegal profiling level value #{level}"
                      end
-      doc = @db.db_command(oh)
+      doc = @db.command(oh)
       raise "Error with profile command: #{doc.inspect}" unless @db.ok?(doc)
     end
 
@@ -71,7 +71,7 @@ module Mongo
     # problem or returning an interesting hash (see especially the
     # 'result' string value) if all is well.
     def validate_collection(name)
-      doc = @db.db_command(:validate => name)
+      doc = @db.command(:validate => name)
       raise "Error with validate command: #{doc.inspect}" unless @db.ok?(doc)
       result = doc['result']
       raise "Error with validation data: #{doc.inspect}" unless result.kind_of?(String)
diff --git a/lib/mongo/collection.rb b/lib/mongo/collection.rb
index ce6aaa6..704d629 100644
--- a/lib/mongo/collection.rb
+++ b/lib/mongo/collection.rb
@@ -41,6 +41,7 @@ module Mongo
       end
 
       @db, @name  = db, name
+      @connection = @db.connection
       @pk_factory = pk_factory || ObjectID
       @hint = nil
     end
@@ -222,7 +223,7 @@ module Mongo
       BSON.serialize_cstr(message, "#{@db.name}.#{@name}")
       message.put_int(0)
       message.put_array(BSON_SERIALIZER.serialize(selector, false).unpack("C*"))
-      @db.send_message_with_operation(Mongo::Constants::OP_DELETE, message,
+      @connection.send_message_with_operation(Mongo::Constants::OP_DELETE, message,
         "db.#{@db.name}.remove(#{selector.inspect})")
     end
 
@@ -261,10 +262,10 @@ module Mongo
       message.put_array(BSON_SERIALIZER.serialize(selector, false).unpack("C*"))
       message.put_array(BSON_SERIALIZER.serialize(document, false).unpack("C*"))
       if options[:safe]
-        @db.send_message_with_safe_check(Mongo::Constants::OP_UPDATE, message,
+        @connection.send_message_with_safe_check(Mongo::Constants::OP_UPDATE, message, @db.name,
           "db.#{@name}.update(#{selector.inspect}, #{document.inspect})")
       else
-        @db.send_message_with_operation(Mongo::Constants::OP_UPDATE, message, 
+        @connection.send_message_with_operation(Mongo::Constants::OP_UPDATE, message, 
           "db.#{@name}.update(#{selector.inspect}, #{document.inspect})")
       end
     end
@@ -333,7 +334,7 @@ module Mongo
           reduce = Code.new(reduce)
         end
 
-        result = @db.db_command({"group" =>
+        result = @db.command({"group" =>
                                   {
                                     "ns" => @name,
                                     "$reduce" => reduce,
@@ -406,7 +407,7 @@ EOS
       command[:distinct] = @name
       command[:key]        = key.to_s
 
-      @db.db_command(command)["values"]
+      @db.command(command)["values"]
     end
 
     # Rename this collection.
@@ -488,10 +489,10 @@ EOS
       BSON.serialize_cstr(message, "#{@db.name}.#{collection_name}")
       documents.each { |doc| message.put_array(BSON_SERIALIZER.serialize(doc, check_keys).unpack("C*")) }
       if safe
-        @db.send_message_with_safe_check(Mongo::Constants::OP_INSERT, message,
+        @connection.send_message_with_safe_check(Mongo::Constants::OP_INSERT, message, @db.name,
           "db.#{collection_name}.insert(#{documents.inspect})")
       else
-        @db.send_message_with_operation(Mongo::Constants::OP_INSERT, message,
+        @connection.send_message_with_operation(Mongo::Constants::OP_INSERT, message,
           "db.#{collection_name}.insert(#{documents.inspect})")
       end
       documents.collect { |o| o[:_id] || o['_id'] }
diff --git a/lib/mongo/connection.rb b/lib/mongo/connection.rb
index e28650b..d2ba204 100644
--- a/lib/mongo/connection.rb
+++ b/lib/mongo/connection.rb
@@ -14,12 +14,27 @@
 # limitations under the License.
 # ++
 
+require 'set'
+require 'socket'
+require 'monitor'
+
 module Mongo
 
   # A connection to MongoDB.
   class Connection
 
     DEFAULT_PORT = 27017
+    STANDARD_HEADER_SIZE = 16
+    RESPONSE_HEADER_SIZE = 20
+
+    attr_reader :logger, :size, :host, :port, :nodes, :sockets, :checked_out, :reserved_connections
+
+
+    def slave_ok?; @slave_ok; end
+    def auto_reconnect?; @auto_reconnect; end
+    
+    # Counter for generating unique request ids.
+    @@current_request_id = 0
 
     # Create a Mongo database server instance. You specify either one or a
     # pair of servers. If one, you also say if connecting to a slave is
@@ -69,41 +84,50 @@ module Mongo
     # When a DB object first connects to a pair, it will find the master
     # instance and connect to that one.
     def initialize(pair_or_host=nil, port=nil, options={})
-      @pair = case pair_or_host
-               when String
-                 [[pair_or_host, port ? port.to_i : DEFAULT_PORT]]
-               when Hash
-                connections = []
-                connections << pair_val_to_connection(pair_or_host[:left])
-                connections << pair_val_to_connection(pair_or_host[:right])
-                connections
-               when nil
-                 [['localhost', DEFAULT_PORT]]
-               end
+      @nodes = format_pair(pair_or_host)
 
-      @options = options
+      # Host and port of current master.
+      @host = @port = nil
+      
+      # Lock for request ids.
+      @id_lock = Mutex.new
+
+      # Lock for checking master.
+      @master_lock = Mutex.new
+
+      # Pool size and timeout.
+      @size      = options[:pool_size] || 1
+      @timeout   = options[:timeout]   || 1.0
+
+      # Cache of reserved sockets mapped to threads
+      @reserved_connections = {}
+
+      # Mutex for synchronizing pool access
+      @connection_mutex = Monitor.new
+
+      # Condition variable for signal and wait
+      @queue = @connection_mutex.new_cond
+
+      @sockets      = []
+      @checked_out  = []
+
+      # Slave ok can be true only if one node is specified
+      @auto_reconnect = options[:auto_reconnect]
+      @slave_ok = options[:slave_ok] && @nodes.length == 1
+      @logger   = options[:logger] || nil
+      @options  = options
+
+      should_connect = options[:connect].nil? ? true : options[:connect]
+      connect_to_master if should_connect
     end
 
-    # Return the Mongo::DB named +db_name+. The slave_ok and
-    # auto_reconnect options passed in via #new may be overridden here.
-    # See DB#new for other options you can pass in.
-    def db(db_name, options={})
-      DB.new(db_name, @pair, @options.merge(options))
-    end
-    
-    def logger
-      @options[:logger]
-    end
-
-    # Returns a hash containing database names as keys and disk space for
-    # each as values.
+    # Returns a hash with all database names and their respective sizes on
+    # disk.
     def database_info
-      doc = single_db_command('admin', :listDatabases => 1)
-      h = {}
-      doc['databases'].each { |db|
-        h[db['name']] = db['sizeOnDisk'].to_i
-      }
-      h
+      doc = self['admin'].command(:listDatabases => 1)
+      returning({}) do |info|
+        doc['databases'].each { |db| info[db['name']] = db['sizeOnDisk'].to_i }
+      end
     end
 
     # Returns an array of database names.
@@ -111,9 +135,21 @@ module Mongo
       database_info.keys
     end
 
+    # Return the database named +db_name+. The slave_ok and
+    # auto_reconnect options passed in via #new may be overridden here.
+    # See DB#new for other options you can pass in.
+    def db(db_name, options={})
+      DB.new(db_name, self, options.merge(:logger => @logger))
+    end
+
+    # Return the database named +db_name+.
+    def [](db_name)
+      DB.new(db_name, self, :logger => @logger)
+    end
+
     # Drops the database +name+.
     def drop_database(name)
-      single_db_command(name, :dropDatabase => 1)
+      self[name].command(:dropDatabase => 1)
     end
 
     # Copies the database +from+ on the local server to +to+ on the specified +host+.
@@ -124,7 +160,35 @@ module Mongo
       oh[:fromhost] = host
       oh[:fromdb]   = from
       oh[:todb]     = to
-      single_db_command('admin', oh)
+      self["admin"].command(oh)
+    end
+
+    # Increments and returns the next available request id.
+    def get_request_id
+      request_id = ''
+      @id_lock.synchronize do 
+        request_id = @@current_request_id += 1
+      end
+      request_id
+    end
+
+    # Prepares a message for transmission to MongoDB by
+    # constructing a valid message header.
+    def add_message_headers(operation, message)
+      headers = ByteBuffer.new
+
+      # Message size.
+      headers.put_int(16 + message.size)
+
+      # Unique request id.
+      headers.put_int(get_request_id)
+
+      # Response id.
+      headers.put_int(0)
+
+      # Opcode.
+      headers.put_int(operation)
+      message.prepend!(headers)
     end
 
     # Return the build information for the current connection.
@@ -132,14 +196,375 @@ module Mongo
       db("admin").command({:buildinfo => 1}, {:admin => true, :check_response => true})
     end
 
-    # Returns the build version of the current server, using
-    # a ServerVersion object for comparability.
+    # Get the build version of the current server.
+    # Returns a ServerVersion object for comparability.
     def server_version
       ServerVersion.new(server_info["version"])
     end
 
-    protected
 
+    ## Connections and pooling ##
+    
+    # Sends a message to MongoDB.
+    #
+    # Takes a MongoDB opcode, +operation+, a message of class ByteBuffer,
+    # +message+, and an optional formatted +log_message+.
+    def send_message(operation, message, log_message=nil)
+      @logger.debug("  MONGODB #{log_message || message}") if @logger
+
+      packed_message = pack_message(operation, message)
+      socket = checkout
+      send_message_on_socket(packed_message, socket)
+    end
+
+    # Sends a message to MongoDB and returns the response.
+    #
+    # Takes a MongoDB opcode, +operation+, a message of class ByteBuffer,
+    # +message+, an optional formatted +log_message+, and an optional
+    # socket.
+    def receive_message(operation, message, log_msg=nil, sock=nil)
+      @logger.debug("  MONGODB #{log_message || message}") if @logger
+      packed_message = pack_message(operation, message)
+
+      # This code is used only if we're checking for master.
+      if sock
+        @master_lock.synchronize do 
+          response = send_and_receive(packed_message, sock)
+        end
+      else
+        socket = checkout
+        response = send_and_receive(packed_message, socket)
+      end
+      response
+    end
+
+    # Sends a message to MongoDB.
+    #
+    # Takes a MongoDB opcode, +operation+, a message of class ByteBuffer,
+    # +message+, and an optional formatted +log_message+.
+    # Sends the message to the databse, adding the necessary headers.
+    def send_message_with_operation(operation, message, log_message=nil)
+      @logger.debug("  MONGODB #{log_message || message}") if @logger
+      packed_message = pack_message(operation, message)
+      socket = checkout
+      response = send_message_on_socket(packed_message, socket)
+      checkin(socket)
+      response
+    end
+
+    # Sends a message to the database, waits for a response, and raises
+    # and exception if the operation has failed.
+    def send_message_with_safe_check(operation, message, db_name, log_message=nil)
+      message_with_headers = add_message_headers(operation, message)
+      message_with_check   = last_error_message(db_name)
+      @logger.debug("  MONGODB #{log_message || message}") if @logger
+      sock = checkout
+      msg  = message_with_headers.append!(message_with_check).to_s
+      send_message_on_socket(msg, sock)
+      docs, num_received, cursor_id = receive(sock)
+      if num_received == 1 && error = docs[0]['err']
+        raise Mongo::OperationFailure, error
+      end
+      checkin(sock)
+      [docs, num_received, cursor_id]
+    end
+
+    # Send a message to the database and waits for the response.
+    def receive_message_with_operation(operation, message, log_message=nil, socket=nil)
+      message_with_headers = add_message_headers(operation, message).to_s
+      @logger.debug("  MONGODB #{log_message || message}") if @logger
+      sock = socket || checkout
+
+      send_message_on_socket(message_with_headers, sock)
+      receive(sock)
+    end
+
+    # Creates a new socket and tries to connect to master.
+    # If successful, sets @host and @port to master and returns the socket.
+    def connect_to_master
+      @host = @port = nil
+      for node_pair in @nodes
+        host, port = *node_pair
+        begin
+          socket = TCPSocket.new(host, port)
+          socket.setsockopt(Socket::IPPROTO_TCP, Socket::TCP_NODELAY, 1)
+
+          result = self['admin'].command({:ismaster => 1}, false, false, socket)
+          if result['ok'] == 1 && ((is_master = result['ismaster'] == 1) || @slave_ok)
+            @host, @port = host, port
+          end
+
+          # Note: slave_ok can be true only when connecting to a single node.
+          if !@slave_ok && !is_master
+            raise ConfigurationError, "Trying to connect directly to slave; " +
+              "if this is what you want, specify :slave_ok => true."
+          end
+
+          break if is_master || @slave_ok
+        rescue SocketError, SystemCallError, IOError => ex
+          socket.close if socket
+          false
+        end
+      end 
+      raise ConnectionError, "failed to connect to any given host:port" unless socket
+    end
+
+    def master?
+      doc = self['admin'].command(:ismaster => 1)
+      doc['ok'] == 1 && doc['ismaster'] == 1
+    end
+
+    # Returns a string of the form "host:port" that points to the master
+    # database. Works even if this is the master database.
+    def master
+      doc = self['admin'].command(:ismaster => 1)
+      if doc['ok'] == 1 && doc['ismaster'] == 1
+        "#@host:#@port"
+      elsif doc['remote']
+       doc['remote']
+      else
+        raise "Error retrieving master database: #{doc.inspect}"
+      end
+    end
+
+    def connected?
+      @sockets.detect do |sock|
+        sock.is_a? Socket
+      end || (@host && @port)
+    end
+
+    # Close the connection to the database.
+    def close
+      @sockets.each do |sock|
+        sock.close
+      end
+      @host = @port = nil
+      @sockets.clear   
+      @checked_out.clear
+      @reserved_connections.clear
+    end
+
+    # Get a socket from the pool, mapped to the current thread.
+    def checkout
+      if sock = @reserved_connections[Thread.current.object_id]
+        sock
+      else
+        sock = obtain_socket
+        @reserved_connections[Thread.current.object_id] = sock
+      end
+      sock
+    end
+
+    # Return a socket to the pool.
+    def checkin(socket)
+      @connection_mutex.synchronize do 
+        @checked_out.delete(socket)
+        @reserved_connections.delete Thread.current.object_id
+        @queue.signal
+      end
+    end
+
+    # Releases connection for any dead threads.
+    # Called when the connection pool grows too large
+    # and we need additional sockets.
+    def clear_stale_cached_connections!
+      keys = Set.new(@reserved_connections.keys)
+
+      Thread.list.each do |thread|
+        keys.delete(thread.object_id) if thread.alive?
+      end
+      
+      keys.each do |key|
+        next unless @reserved_connections.has_key?(key)
+        checkin(@reserved_connections[key])
+        @reserved_connections.delete(key)
+      end
+    end
+
+    # Adds a new socket to the pool and checks it out.
+    #
+    # This method is called exclusively from #obtain_socket;
+    # therefore, it runs within a mutex, as it must.
+    def checkout_new_socket
+      socket = TCPSocket.new(@host, @port)
+      socket.setsockopt(Socket::IPPROTO_TCP, Socket::TCP_NODELAY, 1)
+      @sockets << socket
+      @checked_out << socket
+      socket
+    end
+
+    # Checks out the first available socket from the pool.
+    #
+    # This method is called exclusively from #obtain_socket;
+    # therefore, it runs within a mutex, as it must.
+    def checkout_existing_socket
+      socket = (@sockets - @checked_out).first
+      @checked_out << socket
+      socket
+    end
+
+    # Check out an existing socket or create a new socket if the maximum
+    # pool size has not been exceeded. Otherwise, wait for the next
+    # available socket.
+    def obtain_socket
+      @connection_mutex.synchronize do 
+        
+        # NOTE: Not certain that this is the best place for reconnect
+        connect_to_master if !connected? && @auto_reconnect
+        loop do 
+          socket = if @checked_out.size < @sockets.size
+                     checkout_existing_socket
+                   elsif @sockets.size < @size
+                     checkout_new_socket
+                   end
+
+          return socket if socket
+          # No connections available; wait.
+          if @queue.wait(@timeout)
+            next
+          else
+            # Try to clear out any stale threads to free up some connections
+            clear_stale_cached_connections!
+            if @size == @sockets.size
+              raise ConnectionTimeoutError, "could not obtain connection within " +
+                "#{@timeout} seconds. The max pool size is currently #{@size}; " +
+                "consider increasing it."
+            end
+          end # if
+        end # loop
+      end #sync
+    end
+
+    def receive(sock)
+      receive_header(sock)
+      number_received, cursor_id = receive_response_header(sock)
+      read_documents(number_received, cursor_id, sock)
+    end
+
+    def receive_header(sock)
+      header = ByteBuffer.new
+      header.put_array(receive_message_on_socket(16, sock).unpack("C*"))
+      unless header.size == STANDARD_HEADER_SIZE
+        raise "Short read for DB response header: " +
+          "expected #{STANDARD_HEADER_SIZE} bytes, saw #{header.size}" 
+      end
+      header.rewind
+      size        = header.get_int
+      request_id  = header.get_int
+      response_to = header.get_int
+      op          = header.get_int
+    end
+
+    def receive_response_header(sock)
+      header_buf = ByteBuffer.new
+      header_buf.put_array(receive_message_on_socket(RESPONSE_HEADER_SIZE, sock).unpack("C*"))
+      if header_buf.length != RESPONSE_HEADER_SIZE
+        raise "Short read for DB response header; " +
+          "expected #{RESPONSE_HEADER_SIZE} bytes, saw #{header_buf.length}"
+      end
+      header_buf.rewind
+      result_flags     = header_buf.get_int
+      cursor_id        = header_buf.get_long
+      starting_from    = header_buf.get_int
+      number_remaining = header_buf.get_int
+      [number_remaining, cursor_id]
+    end
+
+    def read_documents(number_received, cursor_id, sock)
+      docs = []
+      number_remaining = number_received
+      while number_remaining > 0 do
+        buf = ByteBuffer.new
+        buf.put_array(receive_message_on_socket(4, sock).unpack("C*"))
+        buf.rewind
+        size = buf.get_int
+        buf.put_array(receive_message_on_socket(size - 4, sock).unpack("C*"), 4)
+        number_remaining -= 1
+        buf.rewind
+        docs << BSON.new.deserialize(buf)
+      end
+      [docs, number_received, cursor_id]
+    end
+
+    def last_error_message(db_name)
+      message = ByteBuffer.new
+      message.put_int(0)
+      BSON.serialize_cstr(message, "#{db_name}.$cmd")
+      message.put_int(0)
+      message.put_int(-1)
+      message.put_array(BSON_SERIALIZER.serialize({:getlasterror => 1}, false).unpack("C*"))
+      add_message_headers(Mongo::Constants::OP_QUERY, message)
+    end
+
+    # Prepares a message for transmission to MongoDB by
+    # constructing a message header with a new request id.
+    def pack_message(operation, message)
+      headers = ByteBuffer.new
+
+      # Message size.
+      headers.put_int(16 + message.size)
+
+      # Unique request id.
+      headers.put_int(get_request_id)
+
+      # Response id.
+      headers.put_int(0)
+
+      # Opcode.
+      headers.put_int(operation)
+      message.prepend!(headers)
+      message.to_s
+    end
+
+    #def send_and_receive
+    #  send_message_on_socket(packed_message, socket)
+    #  receive_message_on_socket()
+    #end
+
+    # Low-level method for sending a message on a socket.
+    # Requires a packed message and an available socket, 
+    def send_message_on_socket(packed_message, socket)
+      #socket will be connected to master when we receive it
+      #begin
+      socket.send(packed_message, 0)
+      #rescue => ex
+        # close
+        # need to find a way to release the socket here
+        # checkin(socket)
+      #  raise ex
+      #end
+    end
+
+    # Low-level method for receiving data from socket.
+    # Requires length and an available socket.
+    def receive_message_on_socket(length, socket)
+      message = ""
+      while message.length < length do
+        chunk = socket.recv(length - message.length)
+        raise "connection closed" unless chunk.length > 0
+        message += chunk
+      end
+      message
+    end
+
+
+    ## Private helper methods
+
+    # Returns an array of host-port pairs.
+    def format_pair(pair_or_host)
+      case pair_or_host
+        when String
+          [[pair_or_host, port ? port.to_i : DEFAULT_PORT]]
+        when Hash
+         connections = []
+         connections << pair_val_to_connection(pair_or_host[:left])
+         connections << pair_val_to_connection(pair_or_host[:right])
+         connections
+        when nil
+          [['localhost', DEFAULT_PORT]]
+      end
+    end
+    
     # Turns an array containing a host name string and a
     # port number integer into a [host, port] pair array.
     def pair_val_to_connection(a)
@@ -154,20 +579,5 @@ module Mongo
         a
       end
     end
-
-    # Send cmd (a hash, possibly ordered) to the admin database and return
-    # the answer. Raises an error unless the return is "ok" (DB#ok?
-    # returns +true+).
-    def single_db_command(db_name, cmd)
-      db = nil
-      begin
-        db = db(db_name)
-        doc = db.db_command(cmd)
-        raise "error retrieving database info: #{doc.inspect}" unless db.ok?(doc)
-        doc
-      ensure
-        db.close if db
-      end
-    end
   end
 end
diff --git a/lib/mongo/cursor.rb b/lib/mongo/cursor.rb
index ce4adc7..4bba2cb 100644
--- a/lib/mongo/cursor.rb
+++ b/lib/mongo/cursor.rb
@@ -32,6 +32,7 @@ module Mongo
     def initialize(collection, options={})
       @db         = collection.db
       @collection = collection
+      @connection = @db.connection
 
       @selector   = convert_selector_for_query(options[:selector])
       @fields     = convert_fields_for_query(options[:fields])
@@ -43,8 +44,9 @@ module Mongo
       @snapshot   = options[:snapshot]
       @timeout    = options[:timeout]  || false
       @explain    = options[:explain]
+      @socket     = options[:socket]
 
-      @full_collection_name   = "#{@collection.db.name}.#{@collection.name}"
+      @full_collection_name = "#{@collection.db.name}.#{@collection.name}"
       @cache = []
       @closed = false
       @query_run = false
@@ -83,7 +85,7 @@ module Mongo
       command = OrderedHash["count",  @collection.name,
                             "query",  @selector,
                             "fields", @fields]
-      response = @db.db_command(command)
+      response = @db.command(command)
       return response['n'].to_i if response['ok'] == 1
       return 0 if response['errmsg'] == "ns missing"
       raise OperationFailure, "Count failed: #{response['errmsg']}"
@@ -199,7 +201,7 @@ module Mongo
         message.put_int(0)
         message.put_int(1)
         message.put_long(@cursor_id)
-        @db.send_message_with_operation(Mongo::Constants::OP_KILL_CURSORS, message, "cursor.close()")
+        @connection.send_message_with_operation(Mongo::Constants::OP_KILL_CURSORS, message, "cursor.close()")
       end
       @cursor_id = 0
       @closed    = true
@@ -212,7 +214,7 @@ module Mongo
     # See http://www.mongodb.org/display/DOCS/Mongo+Wire+Protocol#MongoWireProtocol-Mongo::Constants::OPQUERY
     def query_opts
       timeout  = @timeout ? 0 : Mongo::Constants::OP_QUERY_NO_CURSOR_TIMEOUT
-      slave_ok = @db.slave_ok? ? Mongo::Constants::OP_QUERY_SLAVE_OK : 0 
+      slave_ok = @connection.slave_ok? ? Mongo::Constants::OP_QUERY_SLAVE_OK : 0 
       slave_ok + timeout
     end
 
@@ -294,7 +296,7 @@ module Mongo
         
       # Cursor id.
       message.put_long(@cursor_id)
-      results, @n_received, @cursor_id = @db.receive_message_with_operation(Mongo::Constants::OP_GET_MORE, message, "cursor.get_more()")
+      results, @n_received, @cursor_id = @connection.receive_message_with_operation(Mongo::Constants::OP_GET_MORE, message, "cursor.get_more()", @socket)
       @cache += results
       close_cursor_if_query_complete
     end
@@ -305,8 +307,8 @@ module Mongo
         false
       else
         message = construct_query_message
-        results, @n_received, @cursor_id = @db.receive_message_with_operation(Mongo::Constants::OP_QUERY, message, 
-            (query_log_message if @db.logger))  
+        results, @n_received, @cursor_id = @connection.receive_message_with_operation(Mongo::Constants::OP_QUERY, message, 
+            (query_log_message if @connection.logger), @socket)  
         @cache += results
         @query_run = true
         close_cursor_if_query_complete
diff --git a/lib/mongo/db.rb b/lib/mongo/db.rb
index 4033903..c39630c 100644
--- a/lib/mongo/db.rb
+++ b/lib/mongo/db.rb
@@ -27,8 +27,6 @@ module Mongo
   # A Mongo database.
   class DB
 
-    STANDARD_HEADER_SIZE = 16
-    RESPONSE_HEADER_SIZE = 20
     SYSTEM_NAMESPACE_COLLECTION = "system.namespaces"
     SYSTEM_INDEX_COLLECTION = "system.indexes"
     SYSTEM_PROFILE_COLLECTION = "system.profile"
@@ -39,11 +37,10 @@ module Mongo
     @@current_request_id = 0
 
     # Strict mode enforces collection existence checks. When +true+,
-    # asking for a collection that does not exist or trying to create a
-    # collection that already exists raises an error.
+    # asking for a collection that does not exist, or trying to create a
+    # collection that already exists, raises an error.
     #
-    # Strict mode is off (+false+) by default. Its value can be changed at
-    # any time.
+    # Strict mode is disabled by default, but enabled (+true+) at any time.
     attr_writer :strict
 
     # Returns the value of the +strict+ flag.
@@ -52,26 +49,16 @@ module Mongo
     # The name of the database.
     attr_reader :name
 
+    # The Mongo::Connection instance connecting to the MongoDB server.
     attr_reader :connection
-
-    # Host to which we are currently connected.
-    attr_reader :host
-    # Port to which we are currently connected.
-    attr_reader :port
-
+    
     # An array of [host, port] pairs.
     attr_reader :nodes
 
-    # The database's socket. For internal (and Cursor) use only.
-    attr_reader :socket
-    
-    # The logger instance if :logger is passed to initialize
+    # The logger instance if :logger is passed to initialize.
     attr_reader :logger
 
-    def slave_ok?; @slave_ok; end
-
-    # A primary key factory object (or +nil+). See the README.doc file or
-    # DB#new for details.
+    # The primary key factory object (or +nil+).
     attr_reader :pk_factory
 
     def pk_factory=(pk_factory)
@@ -91,8 +78,7 @@ module Mongo
     # Options:
     #
     # :strict :: If true, collections must exist to be accessed and must
-    #            not exist to be created. See #collection and
-    #            #create_collection.
+    #            not exist to be created. See #collection and #create_collection.
     #
     # :pk :: A primary key factory object that must respond to :create_pk,
     #        which should take a hash and return a hash which merges the
@@ -119,72 +105,18 @@ module Mongo
     # When a DB object first connects to a pair, it will find the master
     # instance and connect to that one. On socket error or if we recieve a
     # "not master" error, we again find the master of the pair.
-    def initialize(db_name, nodes, options={})
-      case db_name
-      when Symbol, String
-      else
-        raise TypeError, "db_name must be a string or symbol"
-      end
-
-      [" ", ".", "$", "/", "\\"].each do |invalid_char|
-        if db_name.include? invalid_char
-          raise InvalidName, "database names cannot contain the character '#{invalid_char}'"
-        end
-      end
-      if db_name.empty?
-        raise InvalidName, "database name cannot be the empty string"
-      end
-
-      @connection = options[:connection]
-
-      @name, @nodes = db_name, nodes
-      @strict = options[:strict]
+    def initialize(db_name, connection, options={})
+      @name       = validate_db_name(db_name)
+      @connection = connection
+      @strict     = options[:strict]
       @pk_factory = options[:pk]
-      @slave_ok = options[:slave_ok] && @nodes.length == 1 # only OK if one node
-      if options[:auto_reconnect]
-        warn(":auto_reconnect is deprecated. henceforth, any time an operation fails, " + 
-             "the driver will attempt to reconnect master on subsequent operations.")
-      end
-      @semaphore = Mutex.new
-      @socket = nil
-      @logger = options[:logger]
-      @network_timeout = 20
-      connect_to_master
-    end
-
-    def connect_to_master
-      close if @socket
-      @host = @port = nil
-      @nodes.detect { |hp|
-        @host, @port = *hp
-        begin
-          @socket = TCPSocket.new(@host, @port)
-          @socket.setsockopt(Socket::IPPROTO_TCP, Socket::TCP_NODELAY, 1)
-
-          # Check for master. Can't call master? because it uses mutex,
-          # which may already be in use during this call.
-          semaphore_is_locked = @semaphore.locked?
-          @semaphore.unlock if semaphore_is_locked
-          is_master = master?
-          @semaphore.lock if semaphore_is_locked
-
-          if @nodes.length == 1 && !is_master && !@slave_ok
-            raise ConfigurationError, "Trying to connect directly to slave; if this is what you want, specify :slave_ok => true."
-          end
-          is_master || @slave_ok
-        rescue SocketError, SystemCallError, IOError => ex
-          close if @socket
-          false
-        end
-      }
-      raise ConnectionFailure, "error: failed to connect to any given host:port" unless @socket
     end
 
     # Returns true if +username+ has +password+ in
     # +SYSTEM_USER_COLLECTION+. +name+ is username, +password+ is
     # plaintext password.
     def authenticate(username, password)
-      doc = db_command(:getnonce => 1)
+      doc = command(:getnonce => 1)
       raise "error retrieving nonce: #{doc}" unless ok?(doc)
       nonce = doc['nonce']
 
@@ -193,12 +125,12 @@ module Mongo
       auth['user'] = username
       auth['nonce'] = nonce
       auth['key'] = Digest::MD5.hexdigest("#{nonce}#{username}#{hash_password(username, password)}")
-      ok?(db_command(auth))
+      ok?(command(auth))
     end
 
     # Deauthorizes use for this database for this connection.
     def logout
-      doc = db_command(:logout => 1)
+      doc = command(:logout => 1)
       raise "error logging out: #{doc.inspect}" unless ok?(doc)
     end
 
@@ -252,7 +184,7 @@ module Mongo
       # Create new collection
       oh = OrderedHash.new
       oh[:create] = name
-      doc = db_command(oh.merge(options || {}))
+      doc = command(oh.merge(options || {}))
       ok = doc['ok']
       return Collection.new(self, name, @pk_factory) if ok.kind_of?(Numeric) && (ok.to_i == 1 || ok.to_i == 0)
       raise "Error creating collection: #{doc.inspect}"
@@ -276,20 +208,20 @@ module Mongo
     def drop_collection(name)
       return true unless collection_names.include?(name)
 
-      ok?(db_command(:drop => name))
+      ok?(command(:drop => name))
     end
 
     # Returns the error message from the most recently executed database
     # operation for this connection, or +nil+ if there was no error.
     def error
-      doc = db_command(:getlasterror => 1)
+      doc = command(:getlasterror => 1)
       raise "error retrieving last error: #{doc}" unless ok?(doc)
       doc['err']
     end
 
     # Get status information from the last operation on this connection.
     def last_status
-      db_command(:getlasterror => 1)
+      command(:getlasterror => 1)
     end
 
     # Returns +true+ if an error was caused by the most recently executed
@@ -303,7 +235,7 @@ module Mongo
     # Only returns errors that have occured since the last call to
     # DB#reset_error_history - returns +nil+ if there is no such error.
     def previous_error
-      error = db_command(:getpreverror => 1)
+      error = command(:getpreverror => 1)
       if error["err"]
         error
       else
@@ -316,42 +248,7 @@ module Mongo
     # Calls to DB#previous_error will only return errors that have occurred
     # since the most recent call to this method.
     def reset_error_history
-      db_command(:reseterror => 1)
-    end
-
-    # Returns true if this database is a master (or is not paired with any
-    # other database), false if it is a slave.
-    def master?
-      doc = db_command(:ismaster => 1)
-      is_master = doc['ismaster']
-      ok?(doc) && is_master.kind_of?(Numeric) && is_master.to_i == 1
-    end
-
-    # Returns a string of the form "host:port" that points to the master
-    # database. Works even if this is the master database.
-    def master
-      doc = db_command(:ismaster => 1)
-      is_master = doc['ismaster']
-      raise "Error retrieving master database: #{doc.inspect}" unless ok?(doc) && is_master.kind_of?(Numeric)
-      case is_master.to_i
-      when 1
-        "#@host:#@port"
-      else
-        doc['remote']
-      end
-    end
-
-    # Close the connection to the database.
-    def close
-      if @socket
-        s = @socket
-        @socket = nil
-        s.close
-      end
-    end
-
-    def connected?
-      @socket != nil
+      command(:reseterror => 1)
     end
 
     # Returns a Cursor over the query results.
@@ -380,7 +277,7 @@ module Mongo
       oh = OrderedHash.new
       oh[:$eval] = code
       oh[:args] = args
-      doc = db_command(oh)
+      doc = command(oh)
       return doc['retval'] if ok?(doc)
       raise OperationFailure, "eval failed: #{doc['errmsg']}"
     end
@@ -391,7 +288,7 @@ module Mongo
       oh = OrderedHash.new
       oh[:renameCollection] = "#{@name}.#{from}"
       oh[:to] = "#{@name}.#{to}"
-      doc = db_command(oh, true)
+      doc = command(oh, true)
       raise "Error renaming collection: #{doc.inspect}" unless ok?(doc)
     end
 
@@ -401,7 +298,7 @@ module Mongo
       oh = OrderedHash.new
       oh[:deleteIndexes] = collection_name
       oh[:index] = name
-      doc = db_command(oh)
+      doc = command(oh)
       raise "Error with drop_index command: #{doc.inspect}" unless ok?(doc)
     end
 
@@ -428,59 +325,7 @@ module Mongo
     def create_index(collection_name, field_or_spec, unique=false)
       self.collection(collection_name).create_index(field_or_spec, unique)
     end
-
-    # Sends a message to MongoDB.
-    #
-    # Takes a MongoDB opcode, +operation+, a message of class ByteBuffer,
-    # +message+, and an optional formatted +log_message+.
-    # Sends the message to the databse, adding the necessary headers.
-    def send_message_with_operation(operation, message, log_message=nil)
-      message_with_headers = add_message_headers(operation, message).to_s
-      @logger.debug("  MONGODB #{log_message || message}") if @logger
-      @semaphore.synchronize do
-        send_message_on_socket(message_with_headers)
-      end
-    end
-
-    def send_message_with_operation_raw(operation, message, log_message=nil)
-      message_with_headers = add_message_headers_raw(operation, message)
-      @logger.debug("  MONGODB #{log_message || message}") if @logger
-      @semaphore.synchronize do
-        send_message_on_socket(message_with_headers)
-      end
-    end
-
-    # Sends a message to the database, waits for a response, and raises
-    # and exception if the operation has failed.
-    def send_message_with_safe_check(operation, message, log_message=nil)
-      message_with_headers = add_message_headers(operation, message)
-      message_with_check   = last_error_message
-      @logger.debug("  MONGODB #{log_message || message}") if @logger
-      @semaphore.synchronize do
-        send_message_on_socket(message_with_headers.append!(message_with_check).to_s)
-        docs, num_received, cursor_id = receive
-        if num_received == 1 && error = docs[0]['err']
-          if docs[0]['err'] == 'not master'
-            raise ConnectionFailure
-          else
-            raise Mongo::OperationFailure, error
-          end
-        else
-          true
-        end
-      end
-    end
-
-    # Send a message to the database and waits for the response.
-    def receive_message_with_operation(operation, message, log_message=nil)
-      message_with_headers = add_message_headers(operation, message).to_s
-      @logger.debug("  MONGODB #{log_message || message}") if @logger
-      @semaphore.synchronize do
-        send_message_on_socket(message_with_headers)
-        receive
-      end
-    end
-
+    
     # Return +true+ if +doc+ contains an 'ok' field with the value 1.
     def ok?(doc)
       ok = doc['ok']
@@ -490,14 +335,14 @@ module Mongo
     # DB commands need to be ordered, so selector must be an OrderedHash
     # (or a Hash with only one element). What DB commands really need is
     # that the "command" key be first.
-    def db_command(selector, use_admin_db=false)
+    def command(selector, use_admin_db=false, sock=nil)
       if !selector.kind_of?(OrderedHash)
         if !selector.kind_of?(Hash) || selector.keys.length > 1
-          raise "db_command must be given an OrderedHash when there is more than one key"
+          raise "command must be given an OrderedHash when there is more than one key"
         end
       end
 
-      cursor = Cursor.new(Collection.new(self, SYSTEM_COMMAND_COLLECTION), :admin => use_admin_db, :limit => -1, :selector => selector)
+      cursor = Cursor.new(Collection.new(self, SYSTEM_COMMAND_COLLECTION), :admin => use_admin_db, :limit => -1, :selector => selector, :socket => sock)
       cursor.next_object
     end
     
@@ -514,14 +359,14 @@ module Mongo
     #
     # Note: DB commands must start with the "command" key. For this reason,
     # any selector containing more than one key must be an OrderedHash.
-    def command(selector, admin=false, check_response=false)
+    def command(selector, admin=false, check_response=false, sock=nil)
       raise MongoArgumentError, "command must be given a selector" unless selector.is_a?(Hash) && !selector.empty?
       if selector.class.eql?(Hash) && selector.keys.length > 1 
         raise MongoArgumentError, "DB#command requires an OrderedHash when hash contains multiple keys"
       end
 
       result = Cursor.new(system_command_collection, :admin => admin, 
-        :limit => -1, :selector => selector).next_object
+        :limit => -1, :selector => selector, :socket => sock).next_object
 
       if check_response && !ok?(result)
         raise OperationFailure, "Database command '#{selector.keys.first}' failed."
@@ -530,147 +375,18 @@ module Mongo
       end
     end
 
+    # DEPRECATED: please use DB#command instead.
+    def db_command(*args)
+      warn "DB#db_command has been DEPRECATED. Please use DB#command instead."
+      command(args[0], args[1])
+    end
+
     def full_collection_name(collection_name)
       "#{@name}.#{collection_name}"
     end
 
     private
 
-    def receive
-      receive_header
-      number_received, cursor_id = receive_response_header
-      read_documents(number_received, cursor_id)
-    end
-
-    def receive_header
-      header = ByteBuffer.new
-      header.put_array(receive_data_on_socket(16).unpack("C*"))
-      unless header.size == STANDARD_HEADER_SIZE
-        raise "Short read for DB response header: " +
-          "expected #{STANDARD_HEADER_SIZE} bytes, saw #{header.size}" 
-      end
-      header.rewind
-      size        = header.get_int
-      request_id  = header.get_int
-      response_to = header.get_int
-      op          = header.get_int
-    end
-
-    def receive_response_header
-      header_buf = ByteBuffer.new
-      header_buf.put_array(receive_data_on_socket(RESPONSE_HEADER_SIZE).unpack("C*"))
-      if header_buf.length != RESPONSE_HEADER_SIZE
-        raise "Short read for DB response header; " +
-          "expected #{RESPONSE_HEADER_SIZE} bytes, saw #{header_buf.length}"
-      end
-      header_buf.rewind
-      result_flags     = header_buf.get_int
-      cursor_id        = header_buf.get_long
-      starting_from    = header_buf.get_int
-      number_remaining = header_buf.get_int
-      [number_remaining, cursor_id]
-    end
-
-    def read_documents(number_received, cursor_id)
-      docs = []
-      number_remaining = number_received
-      while number_remaining > 0 do
-        buf = ByteBuffer.new
-        buf.put_array(receive_data_on_socket(4).unpack("C*"))
-        buf.rewind
-        size = buf.get_int
-        buf.put_array(receive_data_on_socket(size - 4).unpack("C*"), 4)
-        number_remaining -= 1
-        buf.rewind
-        docs << BSON.new.deserialize(buf)
-      end
-      [docs, number_received, cursor_id]
-    end
-
-    # Sending a message on socket.
-    def send_message_on_socket(packed_message)
-      connect_to_master if !connected?
-      begin
-        @socket.print(packed_message)
-        @socket.flush
-      rescue => ex
-        close
-        raise ConnectionFailure, "Operation failed with the following exception: #{ex}."
-      end
-    end
-
-    # Receive data of specified length on socket.
-    def receive_data_on_socket(length)
-      connect_to_master if !connected?
-      message = ""
-      chunk   = ""
-      while message.length < length do
-        begin
-          chunk = @socket.read(length - message.length)
-          raise ConnectionFailure, "connection closed" unless chunk && chunk.length > 0
-          message += chunk
-        rescue => ex
-          raise ConnectionFailure, "Operation failed with the following exception: #{ex}"
-        end
-      end
-      message
-    end
-
-    # Prepares a message for transmission to MongoDB by
-    # constructing a valid message header.
-    def add_message_headers(operation, message)
-      headers = ByteBuffer.new
-
-      # Message size.
-      headers.put_int(16 + message.size)
-
-      # Unique request id.
-      headers.put_int(get_request_id)
-
-      # Response id.
-      headers.put_int(0)
-
-      # Opcode.
-      headers.put_int(operation)
-      message.prepend!(headers)
-    end
-
-    # Increments and then returns the next available request id.
-    # Note: this method should be called from within a lock.
-    def get_request_id
-      @@current_request_id += 1
-      @@current_request_id
-    end
-
-    # Creates a getlasterror message.
-    def last_error_message
-      generate_last_error_message
-    end
-
-    def generate_last_error_message
-      message = ByteBuffer.new
-      message.put_int(0)
-      BSON.serialize_cstr(message, "#{@name}.$cmd")
-      message.put_int(0)
-      message.put_int(-1)
-      message.put_array(BSON_SERIALIZER.serialize({:getlasterror => 1}, false).unpack("C*"))
-      add_message_headers(Mongo::Constants::OP_QUERY, message)
-    end
-
-    def reset_error_message
-      @@reset_error_message ||= generate_reset_error_message
-    end
-
-    def generate_reset_error_message
-      message = ByteBuffer.new
-      message.put_int(0)
-      BSON.serialize_cstr(message, "#{@name}.$cmd")
-      message.put_int(0)
-      message.put_int(-1)
-      message.put_array(BSON_SERIALIZER.serialize({:reseterror => 1}, false).unpack("C*"))
-      add_message_headers(Mongo::Constants::OP_QUERY, message)
-    end
-
     def hash_password(username, plaintext)
       Digest::MD5.hexdigest("#{username}:mongo:#{plaintext}")
     end
@@ -678,5 +394,19 @@ module Mongo
     def system_command_collection
       Collection.new(self, SYSTEM_COMMAND_COLLECTION)
     end
+
+    def validate_db_name(db_name)
+      unless [String, Symbol].include?(db_name.class)
+        raise TypeError, "db_name must be a string or symbol"
+      end
+
+      [" ", ".", "$", "/", "\\"].each do |invalid_char|
+        if db_name.include? invalid_char
+          raise InvalidName, "database names cannot contain the character '#{invalid_char}'"
+        end
+      end
+      raise InvalidName, "database name cannot be the empty string" if db_name.empty?
+      db_name
+    end
   end
 end
diff --git a/lib/mongo/errors.rb b/lib/mongo/errors.rb
index 326f9d2..69cc9e5 100644
--- a/lib/mongo/errors.rb
+++ b/lib/mongo/errors.rb
@@ -27,6 +27,12 @@ module Mongo
   # Raised when invalid arguments are sent to Mongo Ruby methods.
   class MongoArgumentError < MongoRubyError; end
 
+  # Raised on failures in connection to the database server.
+  class ConnectionError < MongoRubyError; end
+
+  # Raised on failures in connection to the database server.
+  class ConnectionTimeoutError < MongoRubyError; end
+
   # Raised when a database operation fails.
   class OperationFailure < MongoDBError; end
   
diff --git a/lib/mongo/gridfs/grid_store.rb b/lib/mongo/gridfs/grid_store.rb
index 4ae53fa..126026a 100644
--- a/lib/mongo/gridfs/grid_store.rb
+++ b/lib/mongo/gridfs/grid_store.rb
@@ -442,7 +442,7 @@ module GridFS
       md5_command = OrderedHash.new
       md5_command['filemd5'] = @files_id
       md5_command['root'] = @root
-      h['md5'] = @db.db_command(md5_command)['md5']
+      h['md5'] = @db.command(md5_command)['md5']
       h
     end
 
diff --git a/test/test_collection.rb b/test/test_collection.rb
index 2ddf4cb..34f1efc 100644
--- a/test/test_collection.rb
+++ b/test/test_collection.rb
@@ -144,7 +144,7 @@ class TestCollection < Test::Unit::TestCase
 
       # Can't duplicate an index.
       assert_raise OperationFailure do
-        @@test.update({}, {"x" => 10}, :safe => true, :upsert => true)
+        @@test.update({}, {"x" => 10}, :safe => true)
       end
     end
   end
@@ -154,7 +154,6 @@ class TestCollection < Test::Unit::TestCase
 
     @@test.save("hello" => "world")
     @@test.save("hello" => "world")
-    assert(@@db.error.include?("E11000"))
 
     assert_raise OperationFailure do
       @@test.save({"hello" => "world"}, :safe => true)
diff --git a/test/test_connection.rb b/test/test_connection.rb
index 42a5c18..499de84 100644
--- a/test/test_connection.rb
+++ b/test/test_connection.rb
@@ -79,8 +79,7 @@ class TestConnection < Test::Unit::TestCase
     logger = Logger.new(output)
     logger.level = Logger::DEBUG
     db = Connection.new(@host, @port, :logger => logger).db('ruby-mongo-test')
-
-    assert output.string.include?("$cmd.find")
+    assert output.string.include?("admin.$cmd.find")
   end
   
   def test_connection_logger
@@ -106,23 +105,23 @@ class TestConnection < Test::Unit::TestCase
     assert !@mongo.database_names.include?('ruby-mongo-will-be-deleted')
   end
 
-  def test_pair
-    db = Connection.new({:left => ['foo', 123]})
-    pair = db.instance_variable_get('@pair')
-    assert_equal 2, pair.length
-    assert_equal ['foo', 123], pair[0]
-    assert_equal ['localhost', Connection::DEFAULT_PORT], pair[1]
+  def test_nodes
+    db = Connection.new({:left => ['foo', 123]}, nil, :connect => false)
+    nodes = db.nodes
+    assert_equal 2, db.nodes.length
+    assert_equal ['foo', 123], nodes[0]
+    assert_equal ['localhost', Connection::DEFAULT_PORT], nodes[1]
 
-    db = Connection.new({:right => 'bar'})
-    pair = db.instance_variable_get('@pair')
-    assert_equal 2, pair.length
-    assert_equal ['localhost', Connection::DEFAULT_PORT], pair[0]
-    assert_equal ['bar', Connection::DEFAULT_PORT], pair[1]
+    db = Connection.new({:right => 'bar'}, nil, :connect => false)
+    nodes = db.nodes
+    assert_equal 2, nodes.length
+    assert_equal ['localhost', Connection::DEFAULT_PORT], nodes[0]
+    assert_equal ['bar', Connection::DEFAULT_PORT], nodes[1]
 
-    db = Connection.new({:right => ['foo', 123], :left => 'bar'})
-    pair = db.instance_variable_get('@pair')
-    assert_equal 2, pair.length
-    assert_equal ['bar', Connection::DEFAULT_PORT], pair[0]
-    assert_equal ['foo', 123], pair[1]
+    db = Connection.new({:right => ['foo', 123], :left => 'bar'}, nil, :connect => false)
+    nodes = db.nodes
+    assert_equal 2, nodes.length
+    assert_equal ['bar', Connection::DEFAULT_PORT], nodes[0]
+    assert_equal ['foo', 123], nodes[1]
   end
 end
diff --git a/test/test_cursor.rb b/test/test_cursor.rb
index fda57ba..30da2f4 100644
--- a/test/test_cursor.rb
+++ b/test/test_cursor.rb
@@ -246,26 +246,26 @@ class CursorTest < Test::Unit::TestCase
   def test_kill_cursors
     @@coll.drop
 
-    client_cursors = @@db.db_command("cursorInfo" => 1)["clientCursors_size"]
-    by_location = @@db.db_command("cursorInfo" => 1)["byLocation_size"]
+    client_cursors = @@db.command("cursorInfo" => 1)["clientCursors_size"]
+    by_location = @@db.command("cursorInfo" => 1)["byLocation_size"]
 
     10000.times do |i|
       @@coll.insert("i" => i)
     end
 
     assert_equal(client_cursors,
-                 @@db.db_command("cursorInfo" => 1)["clientCursors_size"])
+                 @@db.command("cursorInfo" => 1)["clientCursors_size"])
     assert_equal(by_location,
-                 @@db.db_command("cursorInfo" => 1)["byLocation_size"])
+                 @@db.command("cursorInfo" => 1)["byLocation_size"])
 
     10.times do |i|
       @@coll.find_one()
     end
 
     assert_equal(client_cursors,
-                 @@db.db_command("cursorInfo" => 1)["clientCursors_size"])
+                 @@db.command("cursorInfo" => 1)["clientCursors_size"])
     assert_equal(by_location,
-                 @@db.db_command("cursorInfo" => 1)["byLocation_size"])
+                 @@db.command("cursorInfo" => 1)["byLocation_size"])
 
     10.times do |i|
       a = @@coll.find()
@@ -274,49 +274,49 @@ class CursorTest < Test::Unit::TestCase
     end
 
     assert_equal(client_cursors,
-                 @@db.db_command("cursorInfo" => 1)["clientCursors_size"])
+                 @@db.command("cursorInfo" => 1)["clientCursors_size"])
     assert_equal(by_location,
-                 @@db.db_command("cursorInfo" => 1)["byLocation_size"])
+                 @@db.command("cursorInfo" => 1)["byLocation_size"])
 
     a = @@coll.find()
     a.next_object()
 
     assert_not_equal(client_cursors,
-                     @@db.db_command("cursorInfo" => 1)["clientCursors_size"])
+                     @@db.command("cursorInfo" => 1)["clientCursors_size"])
     assert_not_equal(by_location,
-                     @@db.db_command("cursorInfo" => 1)["byLocation_size"])
+                     @@db.command("cursorInfo" => 1)["byLocation_size"])
 
     a.close()
 
     assert_equal(client_cursors,
-                 @@db.db_command("cursorInfo" => 1)["clientCursors_size"])
+                 @@db.command("cursorInfo" => 1)["clientCursors_size"])
     assert_equal(by_location,
-                 @@db.db_command("cursorInfo" => 1)["byLocation_size"])
+                 @@db.command("cursorInfo" => 1)["byLocation_size"])
 
     a = @@coll.find({}, :limit => 10).next_object()
 
     assert_equal(client_cursors,
-                 @@db.db_command("cursorInfo" => 1)["clientCursors_size"])
+                 @@db.command("cursorInfo" => 1)["clientCursors_size"])
     assert_equal(by_location,
-                 @@db.db_command("cursorInfo" => 1)["byLocation_size"])
+                 @@db.command("cursorInfo" => 1)["byLocation_size"])
 
     @@coll.find() do |cursor|
       cursor.next_object()
     end
 
     assert_equal(client_cursors,
-                 @@db.db_command("cursorInfo" => 1)["clientCursors_size"])
+                 @@db.command("cursorInfo" => 1)["clientCursors_size"])
     assert_equal(by_location,
-                 @@db.db_command("cursorInfo" => 1)["byLocation_size"])
+                 @@db.command("cursorInfo" => 1)["byLocation_size"])
 
     @@coll.find() { |cursor|
       cursor.next_object()
     }
 
     assert_equal(client_cursors,
-                 @@db.db_command("cursorInfo" => 1)["clientCursors_size"])
+                 @@db.command("cursorInfo" => 1)["clientCursors_size"])
     assert_equal(by_location,
-                 @@db.db_command("cursorInfo" => 1)["byLocation_size"])
+                 @@db.command("cursorInfo" => 1)["byLocation_size"])
   end
 
   def test_count_with_fields
diff --git a/test/test_db.rb b/test/test_db.rb
index fdf1e0b..0f1c574 100644
--- a/test/test_db.rb
+++ b/test/test_db.rb
@@ -17,9 +17,10 @@ class DBTest < Test::Unit::TestCase
 
   include Mongo
 
-  @@host = ENV['MONGO_RUBY_DRIVER_HOST'] || 'localhost'
-  @@port = ENV['MONGO_RUBY_DRIVER_PORT'] || Connection::DEFAULT_PORT
-  @@db = Connection.new(@@host, @@port).db('ruby-mongo-test')
+  @@host  = ENV['MONGO_RUBY_DRIVER_HOST'] || 'localhost'
+  @@port  = ENV['MONGO_RUBY_DRIVER_PORT'] || Connection::DEFAULT_PORT
+  @@conn  = Connection.new(@@host, @@port)
+  @@db    = @@conn.db('ruby-mongo-test')
   @@users = @@db.collection('system.users')
 
   def setup
@@ -35,8 +36,8 @@ class DBTest < Test::Unit::TestCase
   end
 
   def test_close
-    @@db.close
-    assert !@@db.connected?
+    @@conn.close
+    assert !@@conn.connected?
     begin
       @@db.collection('test').insert('a' => 1)
       fail "expected 'NilClass' exception"
@@ -52,10 +53,10 @@ class DBTest < Test::Unit::TestCase
     output = StringIO.new
     logger = Logger.new(output)
     logger.level = Logger::DEBUG
-    db = Connection.new(@host, @port, :logger => logger).db('ruby-mongo-test')
-    assert_equal logger, db.logger
+    conn = Connection.new(@host, @port, :logger => logger)
+    assert_equal logger, conn.logger
     
-    db.logger.debug 'testing'
+    conn.logger.debug 'testing'
     assert output.string.include?('testing')
   end
 
@@ -89,12 +90,16 @@ class DBTest < Test::Unit::TestCase
   end
 
   def test_pair
-    @@db.close
+    @@conn.close
     @@users = nil
-    @@db = Connection.new({:left => "this-should-fail", :right => [@@host, @@port]}).db('ruby-mongo-test')
-    assert @@db.connected?
+    @@conn  = Connection.new({:left => "this-should-fail", :right => [@@host, @@port]})
+    @@db    = @@conn['ruby-mongo-test']
+    assert @@conn.connected?
   ensure
-    @@db = Connection.new(@@host, @@port).db('ruby-mongo-test') unless @@db.connected?
+    unless @@conn.connected?
+      @@conn = Connection.new(@@host, @@port) 
+      @@db   = @@conn.db('ruby-mongo-test')
+    end
     @@users = @@db.collection('system.users')
   end
 
@@ -122,7 +127,8 @@ class DBTest < Test::Unit::TestCase
   end
 
   def test_pk_factory_reset
-    db = Connection.new(@@host, @@port).db('ruby-mongo-test')
+    conn = Connection.new(@@host, @@port)
+    db   = conn.db('ruby-mongo-test')
     db.pk_factory = Object.new # first time
     begin
       db.pk_factory = Object.new
@@ -130,7 +136,7 @@ class DBTest < Test::Unit::TestCase
     rescue => ex
       assert_match /can not change PK factory/, ex.to_s
     ensure
-      db.close
+      conn.close
     end
   end
 
@@ -150,12 +156,12 @@ class DBTest < Test::Unit::TestCase
     assert !@@db.error?
     assert_nil @@db.previous_error
 
-    @@db.send(:db_command, :forceerror => 1)
+    @@db.send(:command, :forceerror => 1)
     assert @@db.error?
     assert_not_nil @@db.error
     assert_not_nil @@db.previous_error
 
-    @@db.send(:db_command, :forceerror => 1)
+    @@db.send(:command, :forceerror => 1)
     assert @@db.error?
     assert @@db.error
     prev_error = @@db.previous_error
@@ -192,10 +198,10 @@ class DBTest < Test::Unit::TestCase
     assert !@@db.last_status()["updatedExisting"]
   end
 
-  def test_text_port_number
-    db = DB.new('ruby-mongo-test', [[@@host, @@port.to_s]])
-    # If there is no error, all is well
-    db.collection('users').remove
+  def test_text_port_number_raises_no_errors
+    conn = Connection.new(@@host, @@port.to_s)
+    db   = conn['ruby-mongo-test']
+    assert db.collection('users').remove
   end
 
 end
diff --git a/test/test_db_api.rb b/test/test_db_api.rb
index 6b187ff..b291c04 100644
--- a/test/test_db_api.rb
+++ b/test/test_db_api.rb
@@ -6,11 +6,11 @@ require 'test/unit'
 class DBAPITest < Test::Unit::TestCase
   include Mongo
 
-  @@connection = Connection.new(ENV['MONGO_RUBY_DRIVER_HOST'] || 'localhost',
+  @@conn = Connection.new(ENV['MONGO_RUBY_DRIVER_HOST'] || 'localhost',
                         ENV['MONGO_RUBY_DRIVER_PORT'] || Connection::DEFAULT_PORT)
-  @@db   = @@connection.db("ruby-mongo-test")
+  @@db   = @@conn.db("ruby-mongo-test")
   @@coll = @@db.collection('test')
-  @@version = @@connection.server_version
+  @@version = @@conn.server_version
 
   def setup
     @@coll.remove
@@ -95,7 +95,7 @@ class DBAPITest < Test::Unit::TestCase
     # Can't compare _id values because at insert, an _id was added to @r1 by
     # the database but we don't know what it is without re-reading the record
     # (which is what we are doing right now).
-#     assert_equal doc['_id'], @r1['_id']
+#   assert_equal doc['_id'], @r1['_id']
     assert_equal doc['a'], @r1['a']
   end
 
@@ -489,11 +489,11 @@ class DBAPITest < Test::Unit::TestCase
   end
 
   def test_ismaster
-    assert @@db.master?
+    assert @@conn.master?
   end
 
   def test_master
-    assert_equal "#{@@db.host}:#{@@db.port}", @@db.master
+    assert_equal "#{@@conn.host}:#{@@conn.port}", @@conn.master
   end
 
   def test_where
diff --git a/test/test_slave_connection.rb b/test/test_slave_connection.rb
index caf9af8..84b9340 100644
--- a/test/test_slave_connection.rb
+++ b/test/test_slave_connection.rb
@@ -9,8 +9,8 @@ class SlaveConnectionTest < Test::Unit::TestCase
   def self.connect_to_slave
     @@host = ENV['MONGO_RUBY_DRIVER_HOST'] || 'localhost'
     @@port = ENV['MONGO_RUBY_DRIVER_PORT'] || Connection::DEFAULT_PORT
-    db = Connection.new(@@host, @@port, :slave_ok => true).db('ruby-mongo-demo')
-    !db.master?
+    conn = Connection.new(@@host, @@port, :slave_ok => true)
+    !conn.master?
   end
 
   if self.connect_to_slave
@@ -30,8 +30,8 @@ class SlaveConnectionTest < Test::Unit::TestCase
     puts "Not connected to slave; skipping slave connection tests."
 
     def test_slave_ok_false_on_queries
-      @db = Connection.new(@@host, @@port).db('ruby-mongo-demo')
-      assert !@db.slave_ok?
+      @conn = Connection.new(@@host, @@port)
+      assert !@conn.slave_ok?
     end
   end
 end
diff --git a/test/test_threading.rb b/test/test_threading.rb
index fb2a78c..0e0c7c7 100644
--- a/test/test_threading.rb
+++ b/test/test_threading.rb
@@ -4,14 +4,14 @@ class TestThreading < Test::Unit::TestCase
 
   include Mongo
 
-  @@db = Connection.new.db('ruby-mongo-test')
+  @@db = Connection.new('localhost', 27017, :pool_size => 150, :timeout => 1).db('ruby-mongo-test')
   @@coll = @@db.collection('thread-test-collection')
 
   def set_up_safe_data
     @@db.drop_collection('duplicate')
     @@db.drop_collection('unique')
     @duplicate = @@db.collection('duplicate')
-    @unique    = @@db.collection('unique') 
+    @unique    = @@db.collection('unique')
 
     @duplicate.insert("test" => "insert")
     @duplicate.insert("test" => "update")
diff --git a/test/unit/collection_test.rb b/test/unit/collection_test.rb
index 2d8c0e8..0289d39 100644
--- a/test/unit/collection_test.rb
+++ b/test/unit/collection_test.rb
@@ -1,12 +1,6 @@
 require 'test/test_helper'
 
-class CollectionTest < Test::Unit::TestCase
-
-  class MockDB < DB
-    def connect_to_master
-      true
-    end
-  end
+class ConnectionTest < Test::Unit::TestCase
 
   context "Basic operations: " do 
     setup do 
@@ -14,36 +8,40 @@ class CollectionTest < Test::Unit::TestCase
     end
 
     should "send update message" do 
-      @db = MockDB.new("testing", ['localhost', 27017], :logger => @logger)
+      @conn = Connection.new('localhost', 27017, :logger => @logger, :connect => false)
+      @db   = @conn['testing']
       @coll = @db.collection('books')
-      @db.expects(:send_message_with_operation).with do |op, msg, log| 
+      @conn.expects(:send_message_with_operation).with do |op, msg, log| 
         op == 2001 && log.include?("db.books.update")
       end
       @coll.update({}, {:title => 'Moby Dick'})
     end
 
     should "send insert message" do 
-      @db = MockDB.new("testing", ['localhost', 27017], :logger => @logger)
+      @conn = Connection.new('localhost', 27017, :logger => @logger, :connect => false)
+      @db   = @conn['testing']
       @coll = @db.collection('books')
-      @db.expects(:send_message_with_operation).with do |op, msg, log| 
+      @conn.expects(:send_message_with_operation).with do |op, msg, log| 
         op == 2002 && log.include?("db.books.insert")
       end
       @coll.insert({:title => 'Moby Dick'})
     end
 
     should "send safe update message" do
-      @db = MockDB.new("testing", ['localhost', 27017], :logger => @logger)
+      @conn = Connection.new('localhost', 27017, :logger => @logger, :connect => false)
+      @db   = @conn['testing']
       @coll = @db.collection('books')
-      @db.expects(:send_message_with_safe_check).with do |op, msg, log|
+      @conn.expects(:send_message_with_safe_check).with do |op, msg, db_name, log|
         op == 2001 && log.include?("db.books.update")
       end
       @coll.update({}, {:title => 'Moby Dick'}, :safe => true)
     end
 
     should "send safe insert message" do
-      @db = MockDB.new("testing", ['localhost', 27017], :logger => @logger)
+      @conn = Connection.new('localhost', 27017, :logger => @logger, :connect => false)
+      @db   = @conn['testing']
       @coll = @db.collection('books')
-      @db.expects(:send_message_with_safe_check).with do |op, msg, log|
+      @conn.expects(:send_message_with_safe_check).with do |op, msg, db_name, log|
         op == 2001 && log.include?("db.books.update")
       end
       @coll.update({}, {:title => 'Moby Dick'}, :safe => true)
diff --git a/test/unit/connection_test.rb b/test/unit/connection_test.rb
new file mode 100644
index 0000000..a6690b8
--- /dev/null
+++ b/test/unit/connection_test.rb
@@ -0,0 +1,133 @@
+require 'test/test_helper'
+
+class ConnectionTest < Test::Unit::TestCase
+
+  def new_mock_socket
+    socket = Object.new
+    socket.stubs(:setsockopt).with(Socket::IPPROTO_TCP, Socket::TCP_NODELAY, 1)
+    socket
+  end
+
+  def new_mock_db
+    db = Object.new
+  end
+
+  context "Initialization: " do 
+
+    context "given a single node" do 
+      setup do 
+        @conn = Connection.new('localhost', 27107, :connect => false)
+
+        admin_db = new_mock_db
+        admin_db.expects(:command).returns({'ok' => 1, 'ismaster' => 1})
+        @conn.expects(:[]).with('admin').returns(admin_db)
+        @conn.connect_to_master
+      end
+
+      should "set localhost and port to master" do 
+        assert_equal 'localhost', @conn.host
+        assert_equal 27017, @conn.port
+      end
+
+      should "set connection pool to 1" do 
+        assert_equal 1, @conn.size
+      end
+
+      should "default slave_ok to false" do 
+        assert !@conn.slave_ok?
+      end
+
+      should "default auto_reconnect to false" do 
+        assert !@conn.auto_reconnect? 
+      end
+    end
+  end
+
+  context "Connection pooling: " do 
+    setup do 
+      @conn = Connection.new('localhost', 27107, :connect => false, 
+                                   :pool_size => 3)
+
+      admin_db = new_mock_db
+      admin_db.expects(:command).returns({'ok' => 1, 'ismaster' => 1})
+      @conn.expects(:[]).with('admin').returns(admin_db)
+      @conn.connect_to_master
+    end
+
+    should "check out a new connection" do 
+      socket = @conn.checkout
+      assert @conn.reserved_connections.keys.include? Thread.current.object_id
+    end
+
+    context "with multiple threads" do 
+      setup do 
+        @thread1 = Object.new
+        @thread2 = Object.new
+        @thread3 = Object.new
+        @thread4 = Object.new
+        
+        Thread.stubs(:current).returns(@thread1)
+        @socket1 = @conn.checkout
+        Thread.stubs(:current).returns(@thread2)
+        @socket2 = @conn.checkout
+        Thread.stubs(:current).returns(@thread3)
+        @socket3 = @conn.checkout
+      end
+
+      should "add each thread to the reserved pool" do 
+        assert @conn.reserved_connections.keys.include?(@thread1.object_id)
+        assert @conn.reserved_connections.keys.include?(@thread2.object_id)
+        assert @conn.reserved_connections.keys.include?(@thread3.object_id)
+      end
+
+      should "only add one socket per thread" do 
+        @conn.reserved_connections.values do |socket|
+          assert [@socket1, @socket2, @socket3].include?(socket)
+        end
+      end
+
+      should "check out all sockets" do 
+        assert_equal @conn.sockets.size, @conn.checked_out.size
+        @conn.sockets.each do |sock|
+          assert @conn.checked_out.include?(sock)
+        end
+      end
+
+      should "raise an error if no more sockets can be checked out" do
+        # This can't be tested with mock threads.
+        # Will test in integration tests.
+      end
+
+      context "when releasing dead threads" do 
+        setup do 
+          @thread1.expects(:alive?).returns(false)
+          @thread2.expects(:alive?).returns(true)
+          @thread3.expects(:alive?).returns(true)
+          Thread.expects(:list).returns([@thread1, @thread2, @thread3])
+          @conn.clear_stale_cached_connections!
+        end
+
+        should "return connections for dead threads" do 
+          assert !@conn.checked_out.include?(@socket1)
+          assert_nil @conn.reserved_connections[@thread1.object_id]
+        end
+
+        should "maintain connection for live threads" do 
+          assert @conn.checked_out.include?(@socket2)
+          assert @conn.checked_out.include?(@socket3)
+        end
+      end
+
+      context "when checking in a socket" do 
+        setup do 
+          @conn.checkin(@socket3)
+        end
+
+        should "reduce the number checked out by one" do 
+          assert_equal @conn.checked_out.size, (@conn.sockets.size - 1)
+        end
+      end
+    end
+  end
+end 
+
diff --git a/test/unit/cursor_test.rb b/test/unit/cursor_test.rb
index 1fe011f..cc2e489 100644
--- a/test/unit/cursor_test.rb
+++ b/test/unit/cursor_test.rb
@@ -4,7 +4,8 @@ class TestCursor < Test::Unit::TestCase
 
   context "Cursor options" do 
     setup do 
-      @db         = stub(:name => "testing", :slave_ok? => false)    
+      @connection = stub(:class => Connection)
+      @db         = stub(:name => "testing", :slave_ok? => false, :connection => @connection)    
       @collection = stub(:db => @db, :name => "items")
       @cursor     = Cursor.new(@collection)
     end
@@ -64,39 +65,10 @@ class TestCursor < Test::Unit::TestCase
     end
   end
 
-  context "Query options" do 
-    should "test timeout true and slave_ok false" do 
-      @db = stub(:slave_ok? => false, :name => "testing")
-      @collection = stub(:db => @db, :name => "items")
-      @cursor     = Cursor.new(@collection, :timeout => true)
-      assert_equal 0, @cursor.query_opts
-    end
-
-    should "test timeout false and slave_ok false" do 
-      @db = stub(:slave_ok? => false, :name => "testing")
-      @collection = stub(:db => @db, :name => "items")
-      @cursor     = Cursor.new(@collection, :timeout => false)
-      assert_equal 16, @cursor.query_opts
-    end
-
-    should "set timeout true and slave_ok true" do 
-      @db = stub(:slave_ok? => true, :name => "testing")
-      @collection = stub(:db => @db, :name => "items")
-      @cursor = Cursor.new(@collection, :timeout => true)
-      assert_equal 4, @cursor.query_opts
-    end
-
-    should "set timeout false and slave_ok true" do 
-      @db = stub(:slave_ok? => true, :name => "testing")
-      @collection = stub(:db => @db, :name => "items")
-      @cursor = Cursor.new(@collection, :timeout => false)
-      assert_equal 20, @cursor.query_opts
-    end
-  end
-
   context "Query fields" do 
     setup do 
-      @db = stub(:slave_ok? => true, :name => "testing")
+      @connection = stub(:class => Collection)
+      @db = stub(:slave_ok? => true, :name => "testing", :connection => @connection)
       @collection = stub(:db => @db, :name => "items")
     end
 
diff --git a/test/unit/db_test.rb b/test/unit/db_test.rb
index 2622cbf..7444778 100644
--- a/test/unit/db_test.rb
+++ b/test/unit/db_test.rb
@@ -2,16 +2,6 @@ require 'test/test_helper'
 
 class DBTest < Test::Unit::TestCase
 
-  class MockDB < DB
-    attr_accessor :socket
-
-    def connect_to_master
-      true
-    end
-
-    public :add_message_headers
-  end
-
   def insert_message(db, documents)
     documents = [documents] unless documents.is_a?(Array)
     message = ByteBuffer.new
@@ -23,7 +13,8 @@ class DBTest < Test::Unit::TestCase
 
   context "DB commands" do 
     setup do 
-      @db = MockDB.new("testing", ['localhost', 27017])
+      @conn = stub()
+      @db   = DB.new("testing", @conn)
       @collection = mock()
       @db.stubs(:system_command_collection).returns(@collection)
     end
@@ -43,7 +34,7 @@ class DBTest < Test::Unit::TestCase
     should "create the proper cursor" do 
       @cursor = mock(:next_object => {"ok" => 1})
       Cursor.expects(:new).with(@collection, :admin => true,
-        :limit => -1, :selector => {:buildinfo => 1}).returns(@cursor)
+        :limit => -1, :selector => {:buildinfo => 1}, :socket => nil).returns(@cursor)
       command = {:buildinfo => 1}
       @db.command(command, true)
     end
@@ -51,32 +42,13 @@ class DBTest < Test::Unit::TestCase
     should "raise an error when the command fails" do 
       @cursor = mock(:next_object => {"ok" => 0})
       Cursor.expects(:new).with(@collection, :admin => true,
-        :limit => -1, :selector => {:buildinfo => 1}).returns(@cursor)
+        :limit => -1, :selector => {:buildinfo => 1}, :socket => nil).returns(@cursor)
       assert_raise OperationFailure do 
         command = {:buildinfo => 1}
         @db.command(command, true, true)
       end
     end
   end
-
-  context "safe messages" do
-    setup do
-      @db = MockDB.new("testing", ['localhost', 27017])
-      @collection = mock()
-      @db.stubs(:system_command_collection).returns(@collection)
-    end
-
-    should "receive getlasterror message" do
-      @socket = mock()
-      @socket.stubs(:close)
-      @socket.expects(:flush)
-      @socket.expects(:print).with { |message| message.include?('getlasterror') }
-      @db.socket = @socket
-      @db.stubs(:receive)
-      message = insert_message(@db, {:a => 1})
-      @db.send_message_with_safe_check(Mongo::Constants::OP_QUERY, message)
-    end
-  end
 end