Merge branch 'master' of git://github.com/rails/rails

15 files changed, 870 insertions, 581 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
index 20863e73aa..b8f99adc22 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
@@ -1,7 +1,7 @@
 require 'thread'
 require 'monitor'
 require 'set'
-require 'active_support/core_ext/module/synchronization'
+require 'active_support/core_ext/module/deprecation'
 
 module ActiveRecord
   # Raised when a connection could not be obtained within the connection
@@ -9,6 +9,13 @@ module ActiveRecord
   class ConnectionTimeoutError < ConnectionNotEstablished
   end
 
+  # Raised when a connection pool is full and another connection is requested
+  class PoolFullError < ConnectionNotEstablished
+    def initialize size, timeout
+      super("Connection pool of size #{size} and timeout #{timeout}s is full")
+    end
+  end
+
   module ConnectionAdapters
     # Connection pool base class for managing Active Record database
     # connections.
@@ -57,10 +64,35 @@ module ActiveRecord
     # * +wait_timeout+: number of seconds to block and wait for a connection
     #   before giving up and raising a timeout error (default 5 seconds).
     class ConnectionPool
-      attr_accessor :automatic_reconnect
-      attr_reader :spec, :connections
-      attr_reader :columns, :columns_hash, :primary_keys, :tables
-      attr_reader :column_defaults
+      # Every +frequency+ seconds, the reaper will call +reap+ on +pool+.
+      # A reaper instantiated with a nil frequency will never reap the
+      # connection pool.
+      #
+      # Configure the frequency by setting "reaping_frequency" in your
+      # database yaml file.
+      class Reaper
+        attr_reader :pool, :frequency
+
+        def initialize(pool, frequency)
+          @pool      = pool
+          @frequency = frequency
+        end
+
+        def run
+          return unless frequency
+          Thread.new(frequency, pool) { |t, p|
+            while true
+              sleep t
+              p.reap
+            end
+          }
+        end
+      end
+
+      include MonitorMixin
+
+      attr_accessor :automatic_reconnect, :timeout
+      attr_reader :spec, :connections, :size, :reaper
 
       # Creates a new ConnectionPool object. +spec+ is a ConnectionSpecification
       # object which describes database connection information (e.g. adapter,
@@ -69,88 +101,22 @@ module ActiveRecord
       #
       # The default ConnectionPool maximum size is 5.
       def initialize(spec)
+        super()
+
         @spec = spec
 
         # The cache of reserved connections mapped to threads
         @reserved_connections = {}
 
-        # The mutex used to synchronize pool access
-        @connection_mutex = Monitor.new
-        @queue = @connection_mutex.new_cond
         @timeout = spec.config[:wait_timeout] || 5
+        @reaper  = Reaper.new self, spec.config[:reaping_frequency]
+        @reaper.run
 
         # default max pool size to 5
         @size = (spec.config[:pool] && spec.config[:pool].to_i) || 5
 
         @connections         = []
-        @checked_out         = []
         @automatic_reconnect = true
-        @tables              = {}
-        @visitor             = nil
-
-        @columns     = Hash.new do |h, table_name|
-          h[table_name] = with_connection do |conn|
-
-            # Fetch a list of columns
-            conn.columns(table_name, "#{table_name} Columns").tap do |columns|
-
-              # set primary key information
-              columns.each do |column|
-                column.primary = column.name == primary_keys[table_name]
-              end
-            end
-          end
-        end
-
-        @columns_hash = Hash.new do |h, table_name|
-          h[table_name] = Hash[columns[table_name].map { |col|
-            [col.name, col]
-          }]
-        end
-
-        @column_defaults = Hash.new do |h, table_name|
-          h[table_name] = Hash[columns[table_name].map { |col|
-            [col.name, col.default]
-          }]
-        end
-
-        @primary_keys = Hash.new do |h, table_name|
-          h[table_name] = with_connection do |conn|
-            table_exists?(table_name) ? conn.primary_key(table_name) : 'id'
-          end
-        end
-      end
-
-      # A cached lookup for table existence.
-      def table_exists?(name)
-        return true if @tables.key? name
-
-        with_connection do |conn|
-          conn.tables.each { |table| @tables[table] = true }
-          @tables[name] = true if !@tables.key?(name) && conn.table_exists?(name)
-        end
-
-        @tables.key? name
-      end
-
-      # Clears out internal caches:
-      #
-      #   * columns
-      #   * columns_hash
-      #   * tables
-      def clear_cache!
-        @columns.clear
-        @columns_hash.clear
-        @column_defaults.clear
-        @tables.clear
-      end
-
-      # Clear out internal caches for table with +table_name+.
-      def clear_table_cache!(table_name)
-        @columns.delete table_name
-        @columns_hash.delete table_name
-        @column_defaults.delete table_name
-        @primary_keys.delete table_name
       end
 
       # Retrieve the connection associated with the current thread, or call
@@ -165,7 +131,7 @@ module ActiveRecord
       # Check to see if there is an active connection in this connection
       # pool.
       def active_connection?
-        @reserved_connections.key? current_connection_id
+        active_connections.any?
       end
 
       # Signal that the thread is finished with the current connection.
@@ -181,7 +147,7 @@ module ActiveRecord
       # connection when finished.
       def with_connection
         connection_id = current_connection_id
-        fresh_connection = true unless @reserved_connections[connection_id]
+        fresh_connection = true unless active_connection?
         yield connection
       ensure
         release_connection(connection_id) if fresh_connection
@@ -189,94 +155,80 @@ module ActiveRecord
 
       # Returns true if a connection has already been opened.
       def connected?
-        !@connections.empty?
+        synchronize { @connections.any? }
       end
 
       # Disconnects all connections in the pool, and clears the pool.
       def disconnect!
-        @reserved_connections.each do |name,conn|
-          checkin conn
-        end
-        @reserved_connections = {}
-        @connections.each do |conn|
-          conn.disconnect!
+        synchronize do
+          @reserved_connections = {}
+          @connections.each do |conn|
+            checkin conn
+            conn.disconnect!
+          end
+          @connections = []
         end
-        @connections = []
       end
 
       # Clears the cache which maps classes.
       def clear_reloadable_connections!
-        @reserved_connections.each do |name, conn|
-          checkin conn
-        end
-        @reserved_connections = {}
-        @connections.each do |conn|
-          conn.disconnect! if conn.requires_reloading?
-        end
-        @connections.delete_if do |conn|
-          conn.requires_reloading?
+        synchronize do
+          @reserved_connections = {}
+          @connections.each do |conn|
+            checkin conn
+            conn.disconnect! if conn.requires_reloading?
+          end
+          @connections.delete_if do |conn|
+            conn.requires_reloading?
+          end
         end
       end
 
       # Verify active connections and remove and disconnect connections
       # associated with stale threads.
       def verify_active_connections! #:nodoc:
-        clear_stale_cached_connections!
-        @connections.each do |connection|
-          connection.verify!
+        synchronize do
+          @connections.each do |connection|
+            connection.verify!
+          end
         end
       end
 
-      # Return any checked-out connections back to the pool by threads that
-      # are no longer alive.
-      def clear_stale_cached_connections!
-        keys = @reserved_connections.keys - Thread.list.find_all { |t|
-          t.alive?
-        }.map { |thread| thread.object_id }
-        keys.each do |key|
-          checkin @reserved_connections[key]
-          @reserved_connections.delete(key)
-        end
+      def clear_stale_cached_connections! # :nodoc:
       end
+      deprecate :clear_stale_cached_connections!
 
       # Check-out a database connection from the pool, indicating that you want
       # to use it. You should call #checkin when you no longer need this.
       #
-      # This is done by either returning an existing connection, or by creating
-      # a new connection. If the maximum number of connections for this pool has
-      # already been reached, but the pool is empty (i.e. they're all being used),
-      # then this method will wait until a thread has checked in a connection.
-      # The wait time is bounded however: if no connection can be checked out
-      # within the timeout specified for this pool, then a ConnectionTimeoutError
-      # exception will be raised.
+      # This is done by either returning and leasing existing connection, or by
+      # creating a new connection and leasing it.
+      #
+      # If all connections are leased and the pool is at capacity (meaning the
+      # number of currently leased connections is greater than or equal to the
+      # size limit set), an ActiveRecord::PoolFullError exception will be raised.
       #
       # Returns: an AbstractAdapter object.
       #
       # Raises:
-      # - ConnectionTimeoutError: no connection can be obtained from the pool
-      #   within the timeout period.
+      # - PoolFullError: no connection can be obtained from the pool.
       def checkout
         # Checkout an available connection
-        @connection_mutex.synchronize do
-          loop do
-            conn = if @checked_out.size < @connections.size
-                     checkout_existing_connection
-                   elsif @connections.size < @size
-                     checkout_new_connection
-                   end
-            return conn if conn
-
-            @queue.wait(@timeout)
-
-            if(@checked_out.size < @connections.size)
-              next
-            else
-              clear_stale_cached_connections!
-              if @size == @checked_out.size
-                raise ConnectionTimeoutError, "could not obtain a database connection#{" within #{@timeout} seconds" if @timeout}. The max pool size is currently #{@size}; consider increasing it."
-              end
-            end
+        synchronize do
+          # Try to find a connection that hasn't been leased, and lease it
+          conn = connections.find { |c| c.lease }
+
+          # If all connections were leased, and we have room to expand,
+          # create a new connection and lease it.
+          if !conn && connections.size < size
+            conn = checkout_new_connection
+            conn.lease
+          end
 
+          if conn
+            checkout_and_verify conn
+          else
+            raise PoolFullError.new(size, timeout)
           end
         end
       end
@@ -287,56 +239,69 @@ module ActiveRecord
       # +conn+: an AbstractAdapter object, which was obtained by earlier by
       # calling +checkout+ on this pool.
       def checkin(conn)
-        @connection_mutex.synchronize do
+        synchronize do
           conn.run_callbacks :checkin do
-            @checked_out.delete conn
-            @queue.signal
+            conn.expire
           end
         end
       end
 
-      synchronize :clear_reloadable_connections!, :verify_active_connections!,
-        :connected?, :disconnect!, :with => :@connection_mutex
+      # Remove a connection from the connection pool.  The connection will
+      # remain open and active but will no longer be managed by this pool.
+      def remove(conn)
+        synchronize do
+          @connections.delete conn
 
-      private
+          # FIXME: we might want to store the key on the connection so that removing
+          # from the reserved hash will be a little easier.
+          thread_id = @reserved_connections.keys.find { |k|
+            @reserved_connections[k] == conn
+          }
+          @reserved_connections.delete thread_id if thread_id
+        end
+      end
 
-      def new_connection
-        connection = ActiveRecord::Base.send(spec.adapter_method, spec.config)
+      # Removes dead connections from the pool.  A dead connection can occur
+      # if a programmer forgets to close a connection at the end of a thread
+      # or a thread dies unexpectedly.
+      def reap
+        synchronize do
+          stale = Time.now - @timeout
+          connections.dup.each do |conn|
+            remove conn if conn.in_use? && stale > conn.last_use && !conn.active?
+          end
+        end
+      end
 
-        # TODO: This is a bit icky, and in the long term we may want to change the method
-        #       signature for connections. Also, if we switch to have one visitor per
-        #       connection (and therefore per thread), we can get rid of the thread-local
-        #       variable in Arel::Visitors::ToSql.
-        @visitor ||= connection.class.visitor_for(self)
-        connection.visitor = @visitor
+      private
 
-        connection
+      def new_connection
+        ActiveRecord::Base.send(spec.adapter_method, spec.config)
       end
 
       def current_connection_id #:nodoc:
-        Thread.current.object_id
+        ActiveRecord::Base.connection_id ||= Thread.current.object_id
       end
 
       def checkout_new_connection
         raise ConnectionNotEstablished unless @automatic_reconnect
 
         c = new_connection
+        c.pool = self
         @connections << c
-        checkout_and_verify(c)
-      end
-
-      def checkout_existing_connection
-        c = (@connections - @checked_out).first
-        checkout_and_verify(c)
+        c
       end
 
       def checkout_and_verify(c)
         c.run_callbacks :checkout do
           c.verify!
-          @checked_out << c
         end
         c
       end
+
+      def active_connections
+        @connections.find_all { |c| c.in_use? }
+      end
     end
 
     # ConnectionHandler is a collection of ConnectionPool objects. It is used
@@ -367,10 +332,12 @@ module ActiveRecord
 
       def initialize(pools = {})
         @connection_pools = pools
+        @class_to_pool    = {}
       end
 
       def establish_connection(name, spec)
-        @connection_pools[name] = ConnectionAdapters::ConnectionPool.new(spec)
+        @connection_pools[spec] ||= ConnectionAdapters::ConnectionPool.new(spec)
+        @class_to_pool[name] = @connection_pools[spec]
       end
 
       # Returns true if there are any active connections among the connection
@@ -421,19 +388,20 @@ module ActiveRecord
       # can be used as an argument for establish_connection, for easily
       # re-establishing the connection.
       def remove_connection(klass)
-        pool = @connection_pools.delete(klass.name)
+        pool = @class_to_pool.delete(klass.name)
         return nil unless pool
 
+        @connection_pools.delete pool.spec
         pool.automatic_reconnect = false
         pool.disconnect!
         pool.spec.config
       end
 
       def retrieve_connection_pool(klass)
-        pool = @connection_pools[klass.name]
+        pool = @class_to_pool[klass.name]
         return pool if pool
-        return nil if ActiveRecord::Base == klass
-        retrieve_connection_pool klass.superclass
+        return nil if ActiveRecord::Model == klass
+        retrieve_connection_pool klass.active_record_super
       end
     end
 
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb b/activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb
deleted file mode 100644
index c08c0263b9..0000000000
--- a/activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb
+++ /dev/null
@@ -1,153 +0,0 @@
-module ActiveRecord
-  class Base
-    class ConnectionSpecification #:nodoc:
-      attr_reader :config, :adapter_method
-      def initialize (config, adapter_method)
-        @config, @adapter_method = config, adapter_method
-      end
-    end
-
-    ##
-    # :singleton-method:
-    # The connection handler
-    class_attribute :connection_handler, :instance_writer => false
-    self.connection_handler = ConnectionAdapters::ConnectionHandler.new
-
-    # Returns the connection currently associated with the class. This can
-    # also be used to "borrow" the connection to do database work that isn't
-    # easily done without going straight to SQL.
-    def connection
-      self.class.connection
-    end
-
-    # Establishes the connection to the database. Accepts a hash as input where
-    # the <tt>:adapter</tt> key must be specified with the name of a database adapter (in lower-case)
-    # example for regular databases (MySQL, Postgresql, etc):
-    #
-    #   ActiveRecord::Base.establish_connection(
-    #     :adapter  => "mysql",
-    #     :host     => "localhost",
-    #     :username => "myuser",
-    #     :password => "mypass",
-    #     :database => "somedatabase"
-    #   )
-    #
-    # Example for SQLite database:
-    #
-    #   ActiveRecord::Base.establish_connection(
-    #     :adapter => "sqlite",
-    #     :database  => "path/to/dbfile"
-    #   )
-    #
-    # Also accepts keys as strings (for parsing from YAML for example):
-    #
-    #   ActiveRecord::Base.establish_connection(
-    #     "adapter" => "sqlite",
-    #     "database"  => "path/to/dbfile"
-    #   )
-    #
-    # Or a URL:
-    #
-    #   ActiveRecord::Base.establish_connection(
-    #     "postgres://myuser:mypass@localhost/somedatabase"
-    #   )
-    #
-    # The exceptions AdapterNotSpecified, AdapterNotFound and ArgumentError
-    # may be returned on an error.
-    def self.establish_connection(spec = ENV["DATABASE_URL"])
-      case spec
-        when nil
-          raise AdapterNotSpecified unless defined?(Rails.env)
-          establish_connection(Rails.env)
-        when ConnectionSpecification
-          self.connection_handler.establish_connection(name, spec)
-        when Symbol, String
-          if configuration = configurations[spec.to_s]
-            establish_connection(configuration)
-          elsif spec.is_a?(String) && hash = connection_url_to_hash(spec)
-            establish_connection(hash)
-          else
-            raise AdapterNotSpecified, "#{spec} database is not configured"
-          end
-        else
-          spec = spec.symbolize_keys
-          unless spec.key?(:adapter) then raise AdapterNotSpecified, "database configuration does not specify adapter" end
-
-          begin
-            require "active_record/connection_adapters/#{spec[:adapter]}_adapter"
-          rescue LoadError => e
-            raise "Please install the #{spec[:adapter]} adapter: `gem install activerecord-#{spec[:adapter]}-adapter` (#{e})"
-          end
-
-          adapter_method = "#{spec[:adapter]}_connection"
-          unless respond_to?(adapter_method)
-            raise AdapterNotFound, "database configuration specifies nonexistent #{spec[:adapter]} adapter"
-          end
-
-          remove_connection
-          establish_connection(ConnectionSpecification.new(spec, adapter_method))
-      end
-    end
-
-    def self.connection_url_to_hash(url) # :nodoc:
-      config = URI.parse url
-      adapter = config.scheme
-      adapter = "postgresql" if adapter == "postgres"
-      spec = { :adapter  => adapter,
-               :username => config.user,
-               :password => config.password,
-               :port     => config.port,
-               :database => config.path.sub(%r{^/},""),
-               :host     => config.host }
-      spec.reject!{ |_,value| !value }
-      if config.query
-        options = Hash[config.query.split("&").map{ |pair| pair.split("=") }].symbolize_keys
-        spec.merge!(options)
-      end
-      spec
-    end
-
-    class << self
-      # Returns the connection currently associated with the class. This can
-      # also be used to "borrow" the connection to do database work unrelated
-      # to any of the specific Active Records.
-      def connection
-        retrieve_connection
-      end
-
-      # Returns the configuration of the associated connection as a hash:
-      #
-      #  ActiveRecord::Base.connection_config
-      #  # => {:pool=>5, :timeout=>5000, :database=>"db/development.sqlite3", :adapter=>"sqlite3"}
-      #
-      # Please use only for reading.
-      def connection_config
-        connection_pool.spec.config
-      end
-
-      def connection_pool
-        connection_handler.retrieve_connection_pool(self) or raise ConnectionNotEstablished
-      end
-
-      def retrieve_connection
-        connection_handler.retrieve_connection(self)
-      end
-
-      # Returns true if Active Record is connected.
-      def connected?
-        connection_handler.connected?(self)
-      end
-
-      def remove_connection(klass = self)
-        connection_handler.remove_connection(klass)
-      end
-
-      def clear_active_connections!
-        connection_handler.clear_active_connections!
-      end
-
-      delegate :clear_reloadable_connections!,
-        :clear_all_connections!,:verify_active_connections!, :to => :connection_handler
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
index dc4a53034b..eb8cff9610 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
@@ -130,7 +130,7 @@ module ActiveRecord
       #
       # In order to get around this problem, #transaction will emulate the effect
       # of nested transactions, by using savepoints:
-      # http://dev.mysql.com/doc/refman/5.0/en/savepoints.html
+      # http://dev.mysql.com/doc/refman/5.0/en/savepoint.html
       # Savepoints are supported by MySQL and PostgreSQL, but not SQLite3.
       #
       # It is safe to call this method if a database transaction is already open,
@@ -341,7 +341,7 @@ module ActiveRecord
 
         # Send a rollback message to all records after they have been rolled back. If rollback
         # is false, only rollback records since the last save point.
-        def rollback_transaction_records(rollback) #:nodoc
+        def rollback_transaction_records(rollback)
           if rollback
             records = @_current_transaction_records.flatten
             @_current_transaction_records.clear
@@ -361,7 +361,7 @@ module ActiveRecord
         end
 
         # Send a commit message to all records after they have been committed.
-        def commit_transaction_records #:nodoc
+        def commit_transaction_records
           records = @_current_transaction_records.flatten
           @_current_transaction_records.clear
           unless records.blank?
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
index 82f564e41d..132ca10f79 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
@@ -6,7 +6,7 @@ require 'bigdecimal/util'
 
 module ActiveRecord
   module ConnectionAdapters #:nodoc:
-    class IndexDefinition < Struct.new(:table, :name, :unique, :columns, :lengths) #:nodoc:
+    class IndexDefinition < Struct.new(:table, :name, :unique, :columns, :lengths, :orders) #:nodoc:
     end
 
     # Abstract representation of a column definition. Instances of this type
@@ -46,13 +46,13 @@ module ActiveRecord
     # +change_table+ is actually of this type:
     #
     #   class SomeMigration < ActiveRecord::Migration
-    #     def self.up
+    #     def up
     #       create_table :foo do |t|
     #         puts t.class  # => "ActiveRecord::ConnectionAdapters::TableDefinition"
     #       end
     #     end
     #
-    #     def self.down
+    #     def down
     #       ...
     #     end
     #   end
@@ -66,6 +66,7 @@ module ActiveRecord
 
       def initialize(base)
         @columns = []
+        @columns_hash = {}
         @base = base
       end
 
@@ -86,7 +87,7 @@ module ActiveRecord
 
       # Returns a ColumnDefinition for the column with name +name+.
       def [](name)
-        @columns.find {|column| column.name.to_s == name.to_s}
+        @columns_hash[name.to_s]
       end
 
       # Instantiates a new column for the table.
@@ -224,35 +225,38 @@ module ActiveRecord
       #     t.references :taggable, :polymorphic => { :default => 'Photo' }
       #   end
       def column(name, type, options = {})
-        column = self[name] || ColumnDefinition.new(@base, name, type)
-        if options[:limit]
-          column.limit = options[:limit]
-        elsif native[type.to_sym].is_a?(Hash)
-          column.limit = native[type.to_sym][:limit]
+        name = name.to_s
+        type = type.to_sym
+
+        column = self[name] || new_column_definition(@base, name, type)
+
+        limit = options.fetch(:limit) do
+          native[type][:limit] if native[type].is_a?(Hash)
         end
+
+        column.limit     = limit
         column.precision = options[:precision]
-        column.scale = options[:scale]
-        column.default = options[:default]
-        column.null = options[:null]
-        @columns << column unless @columns.include? column
+        column.scale     = options[:scale]
+        column.default   = options[:default]
+        column.null      = options[:null]
         self
       end
 
       %w( string text integer float decimal datetime timestamp time date binary boolean ).each do |column_type|
         class_eval <<-EOV, __FILE__, __LINE__ + 1
-          def #{column_type}(*args)                                               # def string(*args)
-            options = args.extract_options!                                       #   options = args.extract_options!
-            column_names = args                                                   #   column_names = args
-                                                                                  #
-            column_names.each { |name| column(name, '#{column_type}', options) }  #   column_names.each { |name| column(name, 'string', options) }
-          end                                                                     # end
+          def #{column_type}(*args)                                   # def string(*args)
+            options = args.extract_options!                           #   options = args.extract_options!
+            column_names = args                                       #   column_names = args
+            type = :'#{column_type}'                                  #   type = :string
+            column_names.each { |name| column(name, type, options) }  #   column_names.each { |name| column(name, type, options) }
+          end                                                         # end
         EOV
       end
 
       # Appends <tt>:datetime</tt> columns <tt>:created_at</tt> and
       # <tt>:updated_at</tt> to the table.
       def timestamps(*args)
-        options = args.extract_options!
+        options = { :null => false }.merge(args.extract_options!)
         column(:created_at, :datetime, options)
         column(:updated_at, :datetime, options)
       end
@@ -275,9 +279,16 @@ module ActiveRecord
       end
 
       private
-        def native
-          @base.native_database_types
-        end
+      def new_column_definition(base, name, type)
+        definition = ColumnDefinition.new base, name, type
+        @columns << definition
+        @columns_hash[name] = definition
+        definition
+      end
+
+      def native
+        @base.native_database_types
+      end
     end
 
     # Represents an SQL table in an abstract way for updating a table.
@@ -453,13 +464,13 @@ module ActiveRecord
           def #{column_type}(*args)                                          # def string(*args)
             options = args.extract_options!                                  #   options = args.extract_options!
             column_names = args                                              #   column_names = args
-                                                                             #
+            type = :'#{column_type}'                                         #   type = :string
             column_names.each do |name|                                      #   column_names.each do |name|
-              column = ColumnDefinition.new(@base, name, '#{column_type}')   #     column = ColumnDefinition.new(@base, name, 'string')
+              column = ColumnDefinition.new(@base, name.to_s, type)          #     column = ColumnDefinition.new(@base, name, type)
               if options[:limit]                                             #     if options[:limit]
                 column.limit = options[:limit]                               #       column.limit = options[:limit]
-              elsif native['#{column_type}'.to_sym].is_a?(Hash)              #     elsif native['string'.to_sym].is_a?(Hash)
-                column.limit = native['#{column_type}'.to_sym][:limit]       #       column.limit = native['string'.to_sym][:limit]
+              elsif native[type].is_a?(Hash)                                 #     elsif native[type].is_a?(Hash)
+                column.limit = native[type][:limit]                          #       column.limit = native[type][:limit]
               end                                                            #     end
               column.precision = options[:precision]                         #     column.precision = options[:precision]
               column.scale = options[:scale]                                 #     column.scale = options[:scale]
@@ -479,4 +490,3 @@ module ActiveRecord
 
   end
 end
-
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index 8e3ba1297e..20d3b4a1ef 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -1,4 +1,5 @@
 require 'active_support/core_ext/array/wrap'
+require 'active_support/deprecation/reporting'
 
 module ActiveRecord
   module ConnectionAdapters # :nodoc:
@@ -15,8 +16,6 @@ module ActiveRecord
         table_name[0...table_alias_length].gsub(/\./, '_')
       end
 
-      # def tables(name = nil) end
-
       # Checks to see if the table +table_name+ exists on the database.
       #
       # === Example
@@ -113,7 +112,7 @@ module ActiveRecord
       #   Defaults to +id+. If <tt>:id</tt> is false this option is ignored.
       #
       #   Also note that this just sets the primary key in the table. You additionally
-      #   need to configure the primary key in the model via the +set_primary_key+ macro.
+      #   need to configure the primary key in the model via +self.primary_key=+.
       #   Models do NOT auto-detect the primary key from their table definition.
       #
       # [<tt>:options</tt>]
@@ -302,15 +301,8 @@ module ActiveRecord
       # Adds a new index to the table. +column_name+ can be a single Symbol, or
       # an Array of Symbols.
       #
-      # The index will be named after the table and the first column name,
-      # unless you pass <tt>:name</tt> as an option.
-      #
-      # When creating an index on multiple columns, the first column is used as a name
-      # for the index. For example, when you specify an index on two columns
-      # [<tt>:first</tt>, <tt>:last</tt>], the DBMS creates an index for both columns as well as an
-      # index for the first column <tt>:first</tt>. Using just the first name for this index
-      # makes sense, because you will never have to create a singular index with this
-      # name.
+      # The index will be named after the table and the column name(s), unless
+      # you pass <tt>:name</tt> as an option.
       #
       # ===== Examples
       #
@@ -339,6 +331,14 @@ module ActiveRecord
       #  CREATE INDEX by_name_surname ON accounts(name(10), surname(15))
       #
       # Note: SQLite doesn't support index length
+      #
+      # ====== Creating an index with a sort order (desc or asc, asc is the default)
+      #  add_index(:accounts, [:branch_id, :party_id, :surname], :order => {:branch_id => :desc, :part_id => :asc})
+      # generates
+      #  CREATE INDEX by_branch_desc_party ON accounts(branch_id DESC, party_id ASC, surname)
+      #
+      # Note: mysql doesn't yet support index order (it accepts the syntax but ignores it)
+      #
       def add_index(table_name, column_name, options = {})
         index_name, index_type, index_columns = add_index_options(table_name, column_name, options)
         execute "CREATE #{index_type} INDEX #{quote_column_name(index_name)} ON #{quote_table_name(table_name)} (#{index_columns})"
@@ -405,7 +405,7 @@ module ActiveRecord
 
       def dump_schema_information #:nodoc:
         sm_table = ActiveRecord::Migrator.schema_migrations_table_name
-        migrated = select_values("SELECT version FROM #{sm_table}")
+        migrated = select_values("SELECT version FROM #{sm_table} ORDER BY version")
         migrated.map { |v| "INSERT INTO #{sm_table} (version) VALUES ('#{v}');" }.join("\n\n")
       end
 
@@ -426,6 +426,7 @@ module ActiveRecord
           si_table = Base.table_name_prefix + 'schema_info' + Base.table_name_suffix
 
           if table_exists?(si_table)
+            ActiveRecord::Deprecation.warn "Usage of the schema table `#{si_table}` is deprecated. Please switch to using `schema_migrations` table"
 
             old_version = select_value("SELECT version FROM #{quote_table_name(si_table)}").to_i
             assume_migrated_upto_version(old_version)
@@ -507,8 +508,8 @@ module ActiveRecord
       # ===== Examples
       #  add_timestamps(:suppliers)
       def add_timestamps(table_name)
-        add_column table_name, :created_at, :datetime
-        add_column table_name, :updated_at, :datetime
+        add_column table_name, :created_at, :datetime, :null => false
+        add_column table_name, :updated_at, :datetime, :null => false
       end
 
       # Removes the timestamp columns (created_at and updated_at) from the table definition.
@@ -520,9 +521,29 @@ module ActiveRecord
       end
 
       protected
+        def add_index_sort_order(option_strings, column_names, options = {})
+          if options.is_a?(Hash) && order = options[:order]
+            case order
+            when Hash
+              column_names.each {|name| option_strings[name] += " #{order[name].to_s.upcase}" if order.has_key?(name)}
+            when String
+              column_names.each {|name| option_strings[name] += " #{order.upcase}"}
+            end
+          end
+
+          return option_strings
+        end
+
         # Overridden by the mysql adapter for supporting index lengths
         def quoted_columns_for_index(column_names, options = {})
-          column_names.map {|name| quote_column_name(name) }
+          option_strings = Hash[column_names.map {|name| [name, '']}]
+
+          # add index sort order if supported
+          if supports_index_sort_order?
+            option_strings = add_index_sort_order(option_strings, column_names, options)
+          end
+
+          column_names.map {|name| quote_column_name(name) + option_strings[name]}
         end
 
         def options_include_default?(options)
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index 443e61b527..edea414db7 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -3,12 +3,15 @@ require 'bigdecimal'
 require 'bigdecimal/util'
 require 'active_support/core_ext/benchmark'
 require 'active_support/deprecation'
+require 'active_record/connection_adapters/schema_cache'
+require 'monitor'
 
 module ActiveRecord
   module ConnectionAdapters # :nodoc:
     extend ActiveSupport::Autoload
 
     autoload :Column
+    autoload :ConnectionSpecification
 
     autoload_under 'abstract' do
       autoload :IndexDefinition,  'active_record/connection_adapters/abstract/schema_definitions'
@@ -24,7 +27,6 @@ module ActiveRecord
       autoload :ConnectionPool
       autoload :ConnectionHandler,       'active_record/connection_adapters/abstract/connection_pool'
       autoload :ConnectionManagement,    'active_record/connection_adapters/abstract/connection_pool'
-      autoload :ConnectionSpecification
 
       autoload :QueryCache
     end
@@ -47,39 +49,44 @@ module ActiveRecord
       include DatabaseLimits
       include QueryCache
       include ActiveSupport::Callbacks
+      include MonitorMixin
 
       define_callbacks :checkout, :checkin
 
-      attr_accessor :visitor
-
-      def initialize(connection, logger = nil) #:nodoc:
-        @active = nil
-        @connection, @logger = connection, logger
+      attr_accessor :visitor, :pool
+      attr_reader :schema_cache, :last_use, :in_use
+      alias :in_use? :in_use
+
+      def initialize(connection, logger = nil, pool = nil) #:nodoc:
+        super()
+
+        @active              = nil
+        @connection          = connection
+        @in_use              = false
+        @instrumenter        = ActiveSupport::Notifications.instrumenter
+        @last_use            = false
+        @logger              = logger
+        @open_transactions   = 0
+        @pool                = pool
+        @query_cache         = Hash.new { |h,sql| h[sql] = {} }
         @query_cache_enabled = false
-        @query_cache = Hash.new { |h,sql| h[sql] = {} }
-        @open_transactions = 0
-        @instrumenter = ActiveSupport::Notifications.instrumenter
-        @visitor = nil
-      end
-
-      # Returns a visitor instance for this adaptor, which conforms to the Arel::ToSql interface
-      def self.visitor_for(pool) # :nodoc:
-        adapter = pool.spec.config[:adapter]
-
-        if Arel::Visitors::VISITORS[adapter]
-          ActiveSupport::Deprecation.warn(
-            "Arel::Visitors::VISITORS is deprecated and will be removed. Database adapters " \
-            "should define a visitor_for method which returns the appropriate visitor for " \
-            "the database. For example, MysqlAdapter.visitor_for(pool) returns " \
-            "Arel::Visitors::MySQL.new(pool)."
-          )
-
-          Arel::Visitors::VISITORS[adapter].new(pool)
-        else
-          Arel::Visitors::ToSql.new(pool)
+        @schema_cache        = SchemaCache.new self
+        @visitor             = nil
+      end
+
+      def lease
+        synchronize do
+          unless in_use
+            @in_use   = true
+            @last_use = Time.now
+          end
         end
       end
 
+      def expire
+        @in_use = false
+      end
+
       # Returns the human-readable name of the adapter. Use mixed case - one
       # can always use downcase if needed.
       def adapter_name
@@ -130,6 +137,17 @@ module ActiveRecord
         false
       end
 
+      # Does this adapter support index sort order?
+      def supports_index_sort_order?
+        false
+      end
+
+      # Does this adapter support explain? As of this writing sqlite3,
+      # mysql2, and postgresql are the only ones that do.
+      def supports_explain?
+        false
+      end
+
       # QUOTING ==================================================
 
       # Override to return the quoted table name. Defaults to column quoting.
@@ -238,10 +256,19 @@ module ActiveRecord
         node
       end
 
+      def case_insensitive_comparison(table, attribute, column, value)
+        table[attribute].lower.eq(table.lower(value))
+      end
+
       def current_savepoint_name
         "active_record_#{open_transactions}"
       end
 
+      # Check the connection back in to the connection pool
+      def close
+        pool.checkin self
+      end
+
       protected
 
         def log(sql, name = "SQL", binds = [])
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 4b7c74e0b8..560773ca86 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -4,6 +4,13 @@ module ActiveRecord
   module ConnectionAdapters
     class AbstractMysqlAdapter < AbstractAdapter
       class Column < ConnectionAdapters::Column # :nodoc:
+        attr_reader :collation
+
+        def initialize(name, default, sql_type = nil, null = true, collation = nil)
+          super(name, default, sql_type, null)
+          @collation = collation
+        end
+
         def extract_default(default)
           if sql_type =~ /blob/i || type == :text
             if default.blank?
@@ -28,6 +35,10 @@ module ActiveRecord
           raise NotImplementedError
         end
 
+        def case_sensitive?
+          collation && !collation.match(/_ci$/)
+        end
+
         private
 
         def simplified_type(field_type)
@@ -116,10 +127,7 @@ module ActiveRecord
         super(connection, logger)
         @connection_options, @config = connection_options, config
         @quoted_column_names, @quoted_table_names = {}, {}
-      end
-
-      def self.visitor_for(pool) # :nodoc:
-        Arel::Visitors::MySQL.new(pool)
+        @visitor = Arel::Visitors::MySQL.new self
       end
 
       def adapter_name #:nodoc:
@@ -144,6 +152,12 @@ module ActiveRecord
         true
       end
 
+      # Technically MySQL allows to create indexes with the sort order syntax
+      # but at the moment (5.5) it doesn't yet implement them
+      def supports_index_sort_order?
+        true
+      end
+
       def native_database_types
         NATIVE_DATABASE_TYPES
       end
@@ -157,8 +171,8 @@ module ActiveRecord
       end
 
       # Overridden by the adapters to instantiate their specific Column type.
-      def new_column(field, default, type, null) # :nodoc:
-        Column.new(field, default, type, null)
+      def new_column(field, default, type, null, collation) # :nodoc:
+        Column.new(field, default, type, null, collation)
       end
 
       # Must return the Mysql error number from the exception, if the exception has an
@@ -298,11 +312,11 @@ module ActiveRecord
           sql = "SHOW TABLES"
         end
 
-        select_all(sql).map do |table|
+        select_all(sql).map { |table|
           table.delete('Table_type')
           sql = "SHOW CREATE TABLE #{quote_table_name(table.to_a.first.last)}"
           exec_without_stmt(sql).first['Create Table'] + ";\n\n"
-        end.join("")
+        }.join
       end
 
       # Drops the database specified on the +name+ attribute
@@ -349,8 +363,10 @@ module ActiveRecord
         show_variable 'collation_database'
       end
 
-      def tables(name = nil, database = nil) #:nodoc:
-        sql = ["SHOW TABLES", database].compact.join(' IN ')
+      def tables(name = nil, database = nil, like = nil) #:nodoc:
+        sql = "SHOW TABLES "
+        sql << "IN #{database} " if database
+        sql << "LIKE #{quote(like)}" if like
 
         execute_and_free(sql, 'SCHEMA') do |result|
           result.collect { |field| field.first }
@@ -358,7 +374,8 @@ module ActiveRecord
       end
 
       def table_exists?(name)
-        return true if super
+        return false unless name
+        return true if tables(nil, nil, name).any?
 
         name          = name.to_s
         schema, table = name.split('.', 2)
@@ -368,7 +385,7 @@ module ActiveRecord
           schema = nil
         end
 
-        tables(nil, schema).include? table
+        tables(nil, schema, table).any?
       end
 
       # Returns an array of indexes for the given table.
@@ -393,10 +410,10 @@ module ActiveRecord
 
       # Returns an array of +Column+ objects for the table specified by +table_name+.
       def columns(table_name, name = nil)#:nodoc:
-        sql = "SHOW FIELDS FROM #{quote_table_name(table_name)}"
+        sql = "SHOW FULL FIELDS FROM #{quote_table_name(table_name)}"
         execute_and_free(sql, 'SCHEMA') do |result|
           each_hash(result).map do |field|
-            new_column(field[:Field], field[:Default], field[:Type], field[:Null] == "YES")
+            new_column(field[:Field], field[:Default], field[:Type], field[:Null] == "YES", field[:Collation])
           end
         end
       end
@@ -485,9 +502,14 @@ module ActiveRecord
 
       # Returns a table's primary key and belonging sequence.
       def pk_and_sequence_for(table)
-        execute_and_free("DESCRIBE #{quote_table_name(table)}", 'SCHEMA') do |result|
-          keys = each_hash(result).select { |row| row[:Key] == 'PRI' }.map { |row| row[:Field] }
-          keys.length == 1 ? [keys.first, nil] : nil
+        execute_and_free("SHOW CREATE TABLE #{quote_table_name(table)}", 'SCHEMA') do |result|
+          create_table = each_hash(result).first[:"Create Table"]
+          if create_table.to_s =~ /PRIMARY KEY\s+\((.+)\)/
+            keys = $1.split(",").map { |key| key.gsub(/`/, "") }
+            keys.length == 1 ? [keys.first, nil] : nil
+          else
+            nil
+          end
         end
       end
 
@@ -501,23 +523,43 @@ module ActiveRecord
         Arel::Nodes::Bin.new(node)
       end
 
+      def case_insensitive_comparison(table, attribute, column, value)
+        if column.case_sensitive?
+          super
+        else
+          table[attribute].eq(value)
+        end
+      end
+
       def limited_update_conditions(where_sql, quoted_table_name, quoted_primary_key)
         where_sql
       end
 
       protected
 
+      def add_index_length(option_strings, column_names, options = {})
+        if options.is_a?(Hash) && length = options[:length]
+          case length
+          when Hash
+            column_names.each {|name| option_strings[name] += "(#{length[name]})" if length.has_key?(name)}
+          when Fixnum
+            column_names.each {|name| option_strings[name] += "(#{length})"}
+          end
+        end
+
+        return option_strings
+      end
+
       def quoted_columns_for_index(column_names, options = {})
-        length = options[:length] if options.is_a?(Hash)
+        option_strings = Hash[column_names.map {|name| [name, '']}]
 
-        case length
-        when Hash
-          column_names.map {|name| length[name] ? "#{quote_column_name(name)}(#{length[name]})" : quote_column_name(name) }
-        when Fixnum
-          column_names.map {|name| "#{quote_column_name(name)}(#{length})"}
-        else
-          column_names.map {|name| quote_column_name(name) }
-        end
+        # add index length
+        option_strings = add_index_length(option_strings, column_names, options)
+
+        # add index sort order
+        option_strings = add_index_sort_order(option_strings, column_names, options)
+
+        column_names.map {|name| quote_column_name(name) + option_strings[name]}
       end
 
       def translate_exception(exception, message)
diff --git a/activerecord/lib/active_record/connection_adapters/column.rb b/activerecord/lib/active_record/connection_adapters/column.rb
index a7856539b7..6aa4a2c5b3 100644
--- a/activerecord/lib/active_record/connection_adapters/column.rb
+++ b/activerecord/lib/active_record/connection_adapters/column.rb
@@ -80,9 +80,10 @@ module ActiveRecord
         when :decimal              then klass.value_to_decimal(value)
         when :datetime, :timestamp then klass.string_to_time(value)
         when :time                 then klass.string_to_dummy_time(value)
-        when :date                 then klass.string_to_date(value)
+        when :date                 then klass.value_to_date(value)
         when :binary               then klass.binary_to_string(value)
         when :boolean              then klass.value_to_boolean(value)
+        when :hstore               then klass.cast_hstore(value)
         else value
         end
       end
@@ -97,9 +98,10 @@ module ActiveRecord
         when :decimal              then "#{klass}.value_to_decimal(#{var_name})"
         when :datetime, :timestamp then "#{klass}.string_to_time(#{var_name})"
         when :time                 then "#{klass}.string_to_dummy_time(#{var_name})"
-        when :date                 then "#{klass}.string_to_date(#{var_name})"
+        when :date                 then "#{klass}.value_to_date(#{var_name})"
         when :binary               then "#{klass}.binary_to_string(#{var_name})"
         when :boolean              then "#{klass}.value_to_boolean(#{var_name})"
+        when :hstore               then "#{klass}.cast_hstore(#{var_name})"
         else var_name
         end
       end
@@ -132,11 +134,15 @@ module ActiveRecord
           value
         end
 
-        def string_to_date(string)
-          return string unless string.is_a?(String)
-          return nil if string.empty?
-
-          fast_string_to_date(string) || fallback_string_to_date(string)
+        def value_to_date(value)
+          if value.is_a?(String)
+            return nil if value.empty?
+            fast_string_to_date(value) || fallback_string_to_date(value)
+          elsif value.respond_to?(:to_date)
+            value.to_date
+          else
+            value
+          end
         end
 
         def string_to_time(string)
diff --git a/activerecord/lib/active_record/connection_adapters/connection_specification.rb b/activerecord/lib/active_record/connection_adapters/connection_specification.rb
new file mode 100644
index 0000000000..8491d42b86
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/connection_specification.rb
@@ -0,0 +1,83 @@
+module ActiveRecord
+  module ConnectionAdapters
+    class ConnectionSpecification #:nodoc:
+      attr_reader :config, :adapter_method
+
+      def initialize(config, adapter_method)
+        @config, @adapter_method = config, adapter_method
+      end
+
+      def initialize_dup(original)
+        @config = original.config.dup
+      end
+
+      ##
+      # Builds a ConnectionSpecification from user input
+      class Resolver # :nodoc:
+        attr_reader :config, :klass, :configurations
+
+        def initialize(config, configurations)
+          @config         = config
+          @configurations = configurations
+        end
+
+        def spec
+          case config
+          when nil
+            raise AdapterNotSpecified unless defined?(Rails.env)
+            resolve_string_connection Rails.env
+          when Symbol, String
+            resolve_string_connection config.to_s
+          when Hash
+            resolve_hash_connection config
+          end
+        end
+
+        private
+        def resolve_string_connection(spec) # :nodoc:
+          hash = configurations.fetch(spec) do |k|
+            connection_url_to_hash(k)
+          end
+
+          raise(AdapterNotSpecified, "#{spec} database is not configured") unless hash
+
+          resolve_hash_connection hash
+        end
+
+        def resolve_hash_connection(spec) # :nodoc:
+          spec = spec.symbolize_keys
+
+          raise(AdapterNotSpecified, "database configuration does not specify adapter") unless spec.key?(:adapter)
+
+          begin
+            require "active_record/connection_adapters/#{spec[:adapter]}_adapter"
+          rescue LoadError => e
+            raise LoadError, "Please install the #{spec[:adapter]} adapter: `gem install activerecord-#{spec[:adapter]}-adapter` (#{e.message})", e.backtrace
+          end
+
+          adapter_method = "#{spec[:adapter]}_connection"
+
+          ConnectionSpecification.new(spec, adapter_method)
+        end
+
+        def connection_url_to_hash(url) # :nodoc:
+          config = URI.parse url
+          adapter = config.scheme
+          adapter = "postgresql" if adapter == "postgres"
+          spec = { :adapter  => adapter,
+                   :username => config.user,
+                   :password => config.password,
+                   :port     => config.port,
+                   :database => config.path.sub(%r{^/},""),
+                   :host     => config.host }
+          spec.reject!{ |_,value| !value }
+          if config.query
+            options = Hash[config.query.split("&").map{ |pair| pair.split("=") }].symbolize_keys
+            spec.merge!(options)
+          end
+          spec
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
index 8b574518e5..6086c32dbe 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
@@ -1,12 +1,12 @@
 require 'active_record/connection_adapters/abstract_mysql_adapter'
 
-gem 'mysql2', '~> 0.3.6'
+gem 'mysql2', '~> 0.3.10'
 require 'mysql2'
 
 module ActiveRecord
-  class Base
+  module ConnectionHandling
     # Establishes a connection to the database that's used by all Active Record objects.
-    def self.mysql2_connection(config)
+    def mysql2_connection(config)
       config[:username] = 'root' if config[:username].nil?
 
       if Mysql2::Client.const_defined? :FOUND_ROWS
@@ -35,6 +35,10 @@ module ActiveRecord
         configure_connection
       end
 
+      def supports_explain?
+        true
+      end
+
       # HELPER METHODS ===========================================
 
       def each_hash(result) # :nodoc:
@@ -47,8 +51,8 @@ module ActiveRecord
         end
       end
 
-      def new_column(field, default, type, null) # :nodoc:
-        Column.new(field, default, type, null)
+      def new_column(field, default, type, null, collation) # :nodoc:
+        Column.new(field, default, type, null, collation)
       end
 
       def error_number(exception)
@@ -93,6 +97,80 @@ module ActiveRecord
 
       # DATABASE STATEMENTS ======================================
 
+      def explain(arel, binds = [])
+        sql     = "EXPLAIN #{to_sql(arel)}"
+        start   = Time.now
+        result  = exec_query(sql, 'EXPLAIN', binds)
+        elapsed = Time.now - start
+
+        ExplainPrettyPrinter.new.pp(result, elapsed)
+      end
+
+      class ExplainPrettyPrinter # :nodoc:
+        # Pretty prints the result of a EXPLAIN in a way that resembles the output of the
+        # MySQL shell:
+        #
+        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
+        #   | id | select_type | table | type  | possible_keys | key     | key_len | ref   | rows | Extra       |
+        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
+        #   |  1 | SIMPLE      | users | const | PRIMARY       | PRIMARY | 4       | const |    1 |             |
+        #   |  1 | SIMPLE      | posts | ALL   | NULL          | NULL    | NULL    | NULL  |    1 | Using where |
+        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
+        #   2 rows in set (0.00 sec)
+        #
+        # This is an exercise in Ruby hyperrealism :).
+        def pp(result, elapsed)
+          widths    = compute_column_widths(result)
+          separator = build_separator(widths)
+
+          pp = []
+
+          pp << separator
+          pp << build_cells(result.columns, widths)
+          pp << separator
+
+          result.rows.each do |row|
+            pp << build_cells(row, widths)
+          end
+
+          pp << separator
+          pp << build_footer(result.rows.length, elapsed)
+
+          pp.join("\n") + "\n"
+        end
+
+        private
+
+        def compute_column_widths(result)
+          [].tap do |widths|
+            result.columns.each_with_index do |column, i|
+              cells_in_column = [column] + result.rows.map {|r| r[i].nil? ? 'NULL' : r[i].to_s}
+              widths << cells_in_column.map(&:length).max
+            end
+          end
+        end
+
+        def build_separator(widths)
+          padding = 1
+          '+' + widths.map {|w| '-' * (w + (padding*2))}.join('+') + '+'
+        end
+
+        def build_cells(items, widths)
+          cells = []
+          items.each_with_index do |item, i|
+            item = 'NULL' if item.nil?
+            justifier = item.is_a?(Numeric) ? 'rjust' : 'ljust'
+            cells << item.to_s.send(justifier, widths[i])
+          end
+          '| ' + cells.join(' | ') + ' |'
+        end
+
+        def build_footer(nrows, elapsed)
+          rows_label = nrows == 1 ? 'row' : 'rows'
+          "#{nrows} #{rows_label} in set (%.2f sec)" % elapsed
+        end
+      end
+
       # FIXME: re-enable the following once a "better" query_cache solution is in core
       #
       # The overrides below perform much better than the originals in AbstractAdapter
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
index a1824fe396..e432c5af32 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
@@ -18,9 +18,9 @@ class Mysql
 end
 
 module ActiveRecord
-  class Base
+  module ConnectionHandling
     # Establishes a connection to the database that's used by all Active Record objects.
-    def self.mysql_connection(config) # :nodoc:
+    def mysql_connection(config) # :nodoc:
       config = config.symbolize_keys
       host     = config[:host]
       port     = config[:port]
@@ -150,8 +150,8 @@ module ActiveRecord
         end
       end
 
-      def new_column(field, default, type, null) # :nodoc:
-        Column.new(field, default, type, null)
+      def new_column(field, default, type, null, collation) # :nodoc:
+        Column.new(field, default, type, null, collation)
       end
 
       def error_number(exception) # :nodoc:
@@ -224,52 +224,48 @@ module ActiveRecord
         @statements.clear
       end
 
-      if "<3".respond_to?(:encode)
-        # Taken from here:
-        #   https://github.com/tmtm/ruby-mysql/blob/master/lib/mysql/charset.rb
-        # Author: TOMITA Masahiro <tommy@tmtm.org>
-        ENCODINGS = {
-          "armscii8" => nil,
-          "ascii"    => Encoding::US_ASCII,
-          "big5"     => Encoding::Big5,
-          "binary"   => Encoding::ASCII_8BIT,
-          "cp1250"   => Encoding::Windows_1250,
-          "cp1251"   => Encoding::Windows_1251,
-          "cp1256"   => Encoding::Windows_1256,
-          "cp1257"   => Encoding::Windows_1257,
-          "cp850"    => Encoding::CP850,
-          "cp852"    => Encoding::CP852,
-          "cp866"    => Encoding::IBM866,
-          "cp932"    => Encoding::Windows_31J,
-          "dec8"     => nil,
-          "eucjpms"  => Encoding::EucJP_ms,
-          "euckr"    => Encoding::EUC_KR,
-          "gb2312"   => Encoding::EUC_CN,
-          "gbk"      => Encoding::GBK,
-          "geostd8"  => nil,
-          "greek"    => Encoding::ISO_8859_7,
-          "hebrew"   => Encoding::ISO_8859_8,
-          "hp8"      => nil,
-          "keybcs2"  => nil,
-          "koi8r"    => Encoding::KOI8_R,
-          "koi8u"    => Encoding::KOI8_U,
-          "latin1"   => Encoding::ISO_8859_1,
-          "latin2"   => Encoding::ISO_8859_2,
-          "latin5"   => Encoding::ISO_8859_9,
-          "latin7"   => Encoding::ISO_8859_13,
-          "macce"    => Encoding::MacCentEuro,
-          "macroman" => Encoding::MacRoman,
-          "sjis"     => Encoding::SHIFT_JIS,
-          "swe7"     => nil,
-          "tis620"   => Encoding::TIS_620,
-          "ucs2"     => Encoding::UTF_16BE,
-          "ujis"     => Encoding::EucJP_ms,
-          "utf8"     => Encoding::UTF_8,
-          "utf8mb4"  => Encoding::UTF_8,
-        }
-      else
-        ENCODINGS = Hash.new { |h,k| h[k] = k }
-      end
+      # Taken from here:
+      #   https://github.com/tmtm/ruby-mysql/blob/master/lib/mysql/charset.rb
+      # Author: TOMITA Masahiro <tommy@tmtm.org>
+      ENCODINGS = {
+        "armscii8" => nil,
+        "ascii"    => Encoding::US_ASCII,
+        "big5"     => Encoding::Big5,
+        "binary"   => Encoding::ASCII_8BIT,
+        "cp1250"   => Encoding::Windows_1250,
+        "cp1251"   => Encoding::Windows_1251,
+        "cp1256"   => Encoding::Windows_1256,
+        "cp1257"   => Encoding::Windows_1257,
+        "cp850"    => Encoding::CP850,
+        "cp852"    => Encoding::CP852,
+        "cp866"    => Encoding::IBM866,
+        "cp932"    => Encoding::Windows_31J,
+        "dec8"     => nil,
+        "eucjpms"  => Encoding::EucJP_ms,
+        "euckr"    => Encoding::EUC_KR,
+        "gb2312"   => Encoding::EUC_CN,
+        "gbk"      => Encoding::GBK,
+        "geostd8"  => nil,
+        "greek"    => Encoding::ISO_8859_7,
+        "hebrew"   => Encoding::ISO_8859_8,
+        "hp8"      => nil,
+        "keybcs2"  => nil,
+        "koi8r"    => Encoding::KOI8_R,
+        "koi8u"    => Encoding::KOI8_U,
+        "latin1"   => Encoding::ISO_8859_1,
+        "latin2"   => Encoding::ISO_8859_2,
+        "latin5"   => Encoding::ISO_8859_9,
+        "latin7"   => Encoding::ISO_8859_13,
+        "macce"    => Encoding::MacCentEuro,
+        "macroman" => Encoding::MacRoman,
+        "sjis"     => Encoding::SHIFT_JIS,
+        "swe7"     => nil,
+        "tis620"   => Encoding::TIS_620,
+        "ucs2"     => Encoding::UTF_16BE,
+        "ujis"     => Encoding::EucJP_ms,
+        "utf8"     => Encoding::UTF_8,
+        "utf8mb4"  => Encoding::UTF_8,
+      }
 
       # Get the client encoding for this database
       def client_encoding
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 5402918b1d..d2361b5378 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -7,9 +7,9 @@ gem 'pg', '~> 0.11'
 require 'pg'
 
 module ActiveRecord
-  class Base
+  module ConnectionHandling
     # Establishes a connection to the database that's used by all Active Record objects
-    def self.postgresql_connection(config) # :nodoc:
+    def postgresql_connection(config) # :nodoc:
       config = config.symbolize_keys
       host     = config[:host]
       port     = config[:port] || 5432
@@ -49,6 +49,42 @@ module ActiveRecord
             super
           end
         end
+
+        def cast_hstore(object)
+          if Hash === object
+            object.map { |k,v|
+              "#{escape_hstore(k)}=>#{escape_hstore(v)}"
+            }.join ', '
+          else
+            kvs = object.scan(/(?<!\\)".*?(?<!\\)"/).map { |o|
+              unescape_hstore(o[1...-1])
+            }
+            Hash[kvs.each_slice(2).to_a]
+          end
+        end
+
+        private
+        HSTORE_ESCAPE = {
+            ' '  => '\\ ',
+            '\\' => '\\\\',
+            '"'  => '\\"',
+            '='  => '\\=',
+        }
+        HSTORE_ESCAPE_RE   = Regexp.union(HSTORE_ESCAPE.keys)
+        HSTORE_UNESCAPE    = HSTORE_ESCAPE.invert
+        HSTORE_UNESCAPE_RE = Regexp.union(HSTORE_UNESCAPE.keys)
+
+        def unescape_hstore(value)
+          value.gsub(HSTORE_UNESCAPE_RE) do |match|
+            HSTORE_UNESCAPE[match]
+          end
+        end
+
+        def escape_hstore(value)
+          value.gsub(HSTORE_ESCAPE_RE) do |match|
+            HSTORE_ESCAPE[match]
+          end
+        end
       end
       # :startdoc:
 
@@ -79,53 +115,55 @@ module ActiveRecord
         # Maps PostgreSQL-specific data types to logical Rails types.
         def simplified_type(field_type)
           case field_type
-            # Numeric and monetary types
-            when /^(?:real|double precision)$/
-              :float
-            # Monetary types
-            when 'money'
-              :decimal
-            # Character types
-            when /^(?:character varying|bpchar)(?:\(\d+\))?$/
-              :string
-            # Binary data types
-            when 'bytea'
-              :binary
-            # Date/time types
-            when /^timestamp with(?:out)? time zone$/
-              :datetime
-            when 'interval'
-              :string
-            # Geometric types
-            when /^(?:point|line|lseg|box|"?path"?|polygon|circle)$/
-              :string
-            # Network address types
-            when /^(?:cidr|inet|macaddr)$/
-              :string
-            # Bit strings
-            when /^bit(?: varying)?(?:\(\d+\))?$/
-              :string
-            # XML type
-            when 'xml'
-              :xml
-            # tsvector type
-            when 'tsvector'
-              :tsvector
-            # Arrays
-            when /^\D+\[\]$/
-              :string
-            # Object identifier types
-            when 'oid'
-              :integer
-            # UUID type
-            when 'uuid'
-              :string
-            # Small and big integer types
-            when /^(?:small|big)int$/
-              :integer
-            # Pass through all types that are not specific to PostgreSQL.
-            else
-              super
+          # Numeric and monetary types
+          when /^(?:real|double precision)$/
+            :float
+          # Monetary types
+          when 'money'
+            :decimal
+          when 'hstore'
+            :hstore
+          # Character types
+          when /^(?:character varying|bpchar)(?:\(\d+\))?$/
+            :string
+          # Binary data types
+          when 'bytea'
+            :binary
+          # Date/time types
+          when /^timestamp with(?:out)? time zone$/
+            :datetime
+          when 'interval'
+            :string
+          # Geometric types
+          when /^(?:point|line|lseg|box|"?path"?|polygon|circle)$/
+            :string
+          # Network address types
+          when /^(?:cidr|inet|macaddr)$/
+            :string
+          # Bit strings
+          when /^bit(?: varying)?(?:\(\d+\))?$/
+            :string
+          # XML type
+          when 'xml'
+            :xml
+          # tsvector type
+          when 'tsvector'
+            :tsvector
+          # Arrays
+          when /^\D+\[\]$/
+            :string
+          # Object identifier types
+          when 'oid'
+            :integer
+          # UUID type
+          when 'uuid'
+            :string
+          # Small and big integer types
+          when /^(?:small|big)int$/
+            :integer
+          # Pass through all types that are not specific to PostgreSQL.
+          else
+            super
           end
         end
 
@@ -215,6 +253,10 @@ module ActiveRecord
           options = args.extract_options!
           column(args[0], 'tsvector', options)
         end
+
+        def hstore(name, options = {})
+          column(name, 'hstore', options)
+        end
       end
 
       ADAPTER_NAME = 'PostgreSQL'
@@ -247,6 +289,10 @@ module ActiveRecord
         true
       end
 
+      def supports_index_sort_order?
+        true
+      end
+
       class StatementPool < ConnectionAdapters::StatementPool
         def initialize(connection, max)
           super
@@ -278,13 +324,24 @@ module ActiveRecord
           cache.clear
         end
 
+        def delete(sql_key)
+          dealloc cache[sql_key]
+          cache.delete sql_key
+        end
+
         private
         def cache
           @cache[$$]
         end
 
         def dealloc(key)
-          @connection.query "DEALLOCATE #{key}"
+          @connection.query "DEALLOCATE #{key}" if connection_active?
+        end
+
+        def connection_active?
+          @connection.status == PGconn::CONNECTION_OK
+        rescue PGError
+          false
         end
       end
 
@@ -292,6 +349,7 @@ module ActiveRecord
       def initialize(connection, logger, connection_parameters, config)
         super(connection, logger)
         @connection_parameters, @config = connection_parameters, config
+        @visitor = Arel::Visitors::PostgreSQL.new self
 
         # @local_tz is initialized as nil to avoid warnings when connect tries to use it
         @local_tz = nil
@@ -308,10 +366,6 @@ module ActiveRecord
         @local_tz = execute('SHOW TIME ZONE', 'SCHEMA').first["TimeZone"]
       end
 
-      def self.visitor_for(pool) # :nodoc:
-        Arel::Visitors::PostgreSQL.new(pool)
-      end
-
       # Clears the prepared statements cache.
       def clear_cache!
         @statements.clear
@@ -378,6 +432,11 @@ module ActiveRecord
         true
       end
 
+      # Returns true.
+      def supports_explain?
+        true
+      end
+
       # Returns the configured supported identifier length supported by PostgreSQL
       def table_alias_length
         @table_alias_length ||= query('SHOW max_identifier_length')[0][0].to_i
@@ -502,6 +561,48 @@ module ActiveRecord
 
       # DATABASE STATEMENTS ======================================
 
+      def explain(arel, binds = [])
+        sql = "EXPLAIN #{to_sql(arel)}"
+        ExplainPrettyPrinter.new.pp(exec_query(sql, 'EXPLAIN', binds))
+      end
+
+      class ExplainPrettyPrinter # :nodoc:
+        # Pretty prints the result of a EXPLAIN in a way that resembles the output of the
+        # PostgreSQL shell:
+        #
+        #                                     QUERY PLAN
+        #   ------------------------------------------------------------------------------
+        #    Nested Loop Left Join  (cost=0.00..37.24 rows=8 width=0)
+        #      Join Filter: (posts.user_id = users.id)
+        #      ->  Index Scan using users_pkey on users  (cost=0.00..8.27 rows=1 width=4)
+        #            Index Cond: (id = 1)
+        #      ->  Seq Scan on posts  (cost=0.00..28.88 rows=8 width=4)
+        #            Filter: (posts.user_id = 1)
+        #   (6 rows)
+        #
+        def pp(result)
+          header = result.columns.first
+          lines  = result.rows.map(&:first)
+
+          # We add 2 because there's one char of padding at both sides, note
+          # the extra hyphens in the example above.
+          width = [header, *lines].map(&:length).max + 2
+
+          pp = []
+
+          pp << header.center(width).rstrip
+          pp << '-' * width
+
+          pp += lines.map {|line| " #{line}"}
+
+          nrows = result.rows.length
+          rows_label = nrows == 1 ? 'row' : 'rows'
+          pp << "(#{nrows} #{rows_label})"
+
+          pp.join("\n") + "\n"
+        end
+      end
+
       # Executes a SELECT query and returns an array of rows. Each row is an
       # array of field values.
       def select_rows(sql, name = nil)
@@ -743,16 +844,15 @@ module ActiveRecord
 
       # Returns an array of indexes for the given table.
       def indexes(table_name, name = nil)
-         schemas = schema_search_path.split(/,/).map { |p| quote(p) }.join(',')
          result = query(<<-SQL, name)
-           SELECT distinct i.relname, d.indisunique, d.indkey, t.oid
+           SELECT distinct i.relname, d.indisunique, d.indkey, pg_get_indexdef(d.indexrelid), t.oid
            FROM pg_class t
            INNER JOIN pg_index d ON t.oid = d.indrelid
            INNER JOIN pg_class i ON d.indexrelid = i.oid
            WHERE i.relkind = 'i'
              AND d.indisprimary = 'f'
              AND t.relname = '#{table_name}'
-             AND i.relnamespace IN (SELECT oid FROM pg_namespace WHERE nspname IN (#{schemas}) )
+             AND i.relnamespace IN (SELECT oid FROM pg_namespace WHERE nspname = ANY (current_schemas(false)) )
           ORDER BY i.relname
         SQL
 
@@ -761,7 +861,8 @@ module ActiveRecord
           index_name = row[0]
           unique = row[1] == 't'
           indkey = row[2].split(" ")
-          oid = row[3]
+          inddef = row[3]
+          oid = row[4]
 
           columns = Hash[query(<<-SQL, "Columns for index #{row[0]} on #{table_name}")]
           SELECT a.attnum, a.attname
@@ -771,7 +872,12 @@ module ActiveRecord
           SQL
 
           column_names = columns.values_at(*indkey).compact
-          column_names.empty? ? nil : IndexDefinition.new(table_name, index_name, unique, column_names)
+
+          # add info on sort order for columns (only desc order is explicitly specified, asc is the default)
+          desc_order_columns = inddef.scan(/(\w+) DESC/).flatten
+          orders = desc_order_columns.any? ? Hash[desc_order_columns.map {|order_column| [order_column, :desc]}] : {}
+
+          column_names.empty? ? nil : IndexDefinition.new(table_name, index_name, unique, column_names, [], orders)
         end.compact
       end
 
@@ -815,7 +921,7 @@ module ActiveRecord
 
       # Returns the active schema search path.
       def schema_search_path
-        @schema_search_path ||= query('SHOW search_path')[0][0]
+        @schema_search_path ||= query('SHOW search_path', 'SCHEMA')[0][0]
       end
 
       # Returns the current client message level.
@@ -911,12 +1017,14 @@ module ActiveRecord
       # Example:
       #   rename_table('octopuses', 'octopi')
       def rename_table(name, new_name)
+        clear_cache!
         execute "ALTER TABLE #{quote_table_name(name)} RENAME TO #{quote_table_name(new_name)}"
       end
 
       # Adds a new column to the named table.
       # See TableDefinition#column for details of the options you can use.
       def add_column(table_name, column_name, type, options = {})
+        clear_cache!
         add_column_sql = "ALTER TABLE #{quote_table_name(table_name)} ADD COLUMN #{quote_column_name(column_name)} #{type_to_sql(type, options[:limit], options[:precision], options[:scale])}"
         add_column_options!(add_column_sql, options)
 
@@ -925,6 +1033,7 @@ module ActiveRecord
 
       # Changes the column of a table.
       def change_column(table_name, column_name, type, options = {})
+        clear_cache!
         quoted_table_name = quote_table_name(table_name)
 
         execute "ALTER TABLE #{quoted_table_name} ALTER COLUMN #{quote_column_name(column_name)} TYPE #{type_to_sql(type, options[:limit], options[:precision], options[:scale])}"
@@ -935,10 +1044,12 @@ module ActiveRecord
 
       # Changes the default value of a table column.
       def change_column_default(table_name, column_name, default)
+        clear_cache!
         execute "ALTER TABLE #{quote_table_name(table_name)} ALTER COLUMN #{quote_column_name(column_name)} SET DEFAULT #{quote(default)}"
       end
 
       def change_column_null(table_name, column_name, null, default = nil)
+        clear_cache!
         unless null || default.nil?
           execute("UPDATE #{quote_table_name(table_name)} SET #{quote_column_name(column_name)}=#{quote(default)} WHERE #{quote_column_name(column_name)} IS NULL")
         end
@@ -947,6 +1058,7 @@ module ActiveRecord
 
       # Renames a column in a table.
       def rename_column(table_name, column_name, new_column_name)
+        clear_cache!
         execute "ALTER TABLE #{quote_table_name(table_name)} RENAME COLUMN #{quote_column_name(column_name)} TO #{quote_column_name(new_column_name)}"
       end
 
@@ -1030,26 +1142,54 @@ module ActiveRecord
         end
 
       private
+        FEATURE_NOT_SUPPORTED = "0A000" # :nodoc:
+
         def exec_no_cache(sql, binds)
           @connection.async_exec(sql)
         end
 
         def exec_cache(sql, binds)
-          unless @statements.key? sql
-            nextkey = @statements.next_key
-            @connection.prepare nextkey, sql
-            @statements[sql] = nextkey
+          begin
+            stmt_key = prepare_statement sql
+
+            # Clear the queue
+            @connection.get_last_result
+            @connection.send_query_prepared(stmt_key, binds.map { |col, val|
+              type_cast(val, col)
+            })
+            @connection.block
+            @connection.get_last_result
+          rescue PGError => e
+            # Get the PG code for the failure.  Annoyingly, the code for
+            # prepared statements whose return value may have changed is
+            # FEATURE_NOT_SUPPORTED.  Check here for more details:
+            # http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/backend/utils/cache/plancache.c#l573
+            code = e.result.result_error_field(PGresult::PG_DIAG_SQLSTATE)
+            if FEATURE_NOT_SUPPORTED == code
+              @statements.delete sql_key(sql)
+              retry
+            else
+              raise e
+            end
           end
+        end
 
-          key = @statements[sql]
+        # Returns the statement identifier for the client side cache
+        # of statements
+        def sql_key(sql)
+          "#{schema_search_path}-#{sql}"
+        end
 
-          # Clear the queue
-          @connection.get_last_result
-          @connection.send_query_prepared(key, binds.map { |col, val|
-            type_cast(val, col)
-          })
-          @connection.block
-          @connection.get_last_result
+        # Prepare the statement if it hasn't been prepared, return
+        # the statement key.
+        def prepare_statement(sql)
+          sql_key = sql_key(sql)
+          unless @statements.key? sql_key
+            nextkey = @statements.next_key
+            @connection.prepare nextkey, sql
+            @statements[sql_key] = nextkey
+          end
+          @statements[sql_key]
         end
 
         # The internal PostgreSQL identifier of the money data type.
diff --git a/activerecord/lib/active_record/connection_adapters/schema_cache.rb b/activerecord/lib/active_record/connection_adapters/schema_cache.rb
new file mode 100644
index 0000000000..4e8932a695
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/schema_cache.rb
@@ -0,0 +1,50 @@
+module ActiveRecord
+  module ConnectionAdapters
+    class SchemaCache
+      attr_reader :columns, :columns_hash, :primary_keys, :tables
+      attr_reader :connection
+
+      def initialize(conn)
+        @connection = conn
+        @tables     = {}
+
+        @columns = Hash.new do |h, table_name|
+          h[table_name] = conn.columns(table_name, "#{table_name} Columns")
+        end
+
+        @columns_hash = Hash.new do |h, table_name|
+          h[table_name] = Hash[columns[table_name].map { |col|
+            [col.name, col]
+          }]
+        end
+
+        @primary_keys = Hash.new do |h, table_name|
+          h[table_name] = table_exists?(table_name) ? conn.primary_key(table_name) : nil
+        end
+      end
+
+      # A cached lookup for table existence.
+      def table_exists?(name)
+        return @tables[name] if @tables.key? name
+
+        @tables[name] = connection.table_exists?(name)
+      end
+
+      # Clears out internal caches
+      def clear!
+        @columns.clear
+        @columns_hash.clear
+        @primary_keys.clear
+        @tables.clear
+      end
+
+      # Clear out internal caches for table with +table_name+.
+      def clear_table_cache!(table_name)
+        @columns.delete table_name
+        @columns_hash.delete table_name
+        @primary_keys.delete table_name
+        @tables.delete table_name
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
index 0a0da0b5d3..ee5d10859c 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
@@ -1,12 +1,12 @@
 require 'active_record/connection_adapters/sqlite_adapter'
 
-gem 'sqlite3', '~> 1.3.4'
+gem 'sqlite3', '~> 1.3.5'
 require 'sqlite3'
 
 module ActiveRecord
-  class Base
+  module ConnectionHandling
     # sqlite3 adapter reuses sqlite_connection.
-    def self.sqlite3_connection(config) # :nodoc:
+    def sqlite3_connection(config) # :nodoc:
       # Require database.
       unless config[:database]
         raise ArgumentError, "No database file specified. Missing argument: database"
@@ -47,11 +47,7 @@ module ActiveRecord
 
       # Returns the current database encoding format as a string, eg: 'UTF-8'
       def encoding
-        if @connection.respond_to?(:encoding)
-          @connection.encoding.to_s
-        else
-          @connection.execute('PRAGMA encoding')[0]['encoding']
-        end
+        @connection.encoding.to_s
       end
 
     end
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
index 1932a849ee..69750a911d 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
@@ -16,7 +16,7 @@ module ActiveRecord
         end
 
         def binary_to_string(value)
-          if value.respond_to?(:force_encoding) && value.encoding != Encoding::ASCII_8BIT
+          if value.encoding != Encoding::ASCII_8BIT
             value = value.force_encoding(Encoding::ASCII_8BIT)
           end
 
@@ -89,10 +89,7 @@ module ActiveRecord
         @statements = StatementPool.new(@connection,
                                         config.fetch(:statement_limit) { 1000 })
         @config = config
-      end
-
-      def self.visitor_for(pool) # :nodoc:
-        Arel::Visitors::SQLite.new(pool)
+        @visitor = Arel::Visitors::SQLite.new self
       end
 
       def adapter_name #:nodoc:
@@ -125,6 +122,11 @@ module ActiveRecord
         true
       end
 
+      # Returns true.
+      def supports_explain?
+        true
+      end
+
       def requires_reloading?
         true
       end
@@ -157,6 +159,10 @@ module ActiveRecord
         sqlite_version >= '3.1.0'
       end
 
+      def supports_index_sort_order?
+        sqlite_version >= '3.3.0'
+      end
+
       def native_database_types #:nodoc:
         {
           :primary_key => default_primary_key_type,
@@ -195,29 +201,40 @@ module ActiveRecord
         end
       end
 
-      if "<3".encoding_aware?
-        def type_cast(value, column) # :nodoc:
-          return value.to_f if BigDecimal === value
-          return super unless String === value
-          return super unless column && value
-
-          value = super
-          if column.type == :string && value.encoding == Encoding::ASCII_8BIT
-            @logger.error "Binary data inserted for `string` type on column `#{column.name}`"
-            value.encode! 'utf-8'
-          end
-          value
-        end
-      else
-        def type_cast(value, column) # :nodoc:
-          return super unless BigDecimal === value
+      def type_cast(value, column) # :nodoc:
+        return value.to_f if BigDecimal === value
+        return super unless String === value
+        return super unless column && value
 
-          value.to_f
+        value = super
+        if column.type == :string && value.encoding == Encoding::ASCII_8BIT
+          @logger.error "Binary data inserted for `string` type on column `#{column.name}`"
+          value.encode! 'utf-8'
         end
+        value
       end
 
       # DATABASE STATEMENTS ======================================
 
+      def explain(arel, binds = [])
+        sql = "EXPLAIN QUERY PLAN #{to_sql(arel)}"
+        ExplainPrettyPrinter.new.pp(exec_query(sql, 'EXPLAIN', binds))
+      end
+
+      class ExplainPrettyPrinter
+        # Pretty prints the result of a EXPLAIN QUERY PLAN in a way that resembles
+        # the output of the SQLite shell:
+        #
+        #   0|0|0|SEARCH TABLE users USING INTEGER PRIMARY KEY (rowid=?) (~1 rows)
+        #   0|1|1|SCAN TABLE posts (~100000 rows)
+        #
+        def pp(result) # :nodoc:
+          result.rows.map do |row|
+            row.join('|')
+          end.join("\n") + "\n"
+        end
+      end
+
       def exec_query(sql, name = nil, binds = [])
         log(sql, name, binds) do
 
@@ -304,18 +321,23 @@ module ActiveRecord
 
       # SCHEMA STATEMENTS ========================================
 
-      def tables(name = 'SCHEMA') #:nodoc:
+      def tables(name = 'SCHEMA', table_name = nil) #:nodoc:
         sql = <<-SQL
           SELECT name
           FROM sqlite_master
           WHERE type = 'table' AND NOT name = 'sqlite_sequence'
         SQL
+        sql << " AND name = #{quote_table_name(table_name)}" if table_name
 
         exec_query(sql, name).map do |row|
           row['name']
         end
       end
 
+      def table_exists?(name)
+        name && tables('SCHEMA', name).any?
+      end
+
       # Returns an array of +SQLiteColumn+ objects for the table specified by +table_name+.
       def columns(table_name, name = nil) #:nodoc:
         table_structure(table_name).map do |field|
@@ -413,6 +435,8 @@ module ActiveRecord
             self.limit   = options[:limit] if options.include?(:limit)
             self.default = options[:default] if include_default
             self.null    = options[:null] if options.include?(:null)
+            self.precision = options[:precision] if options.include?(:precision)
+            self.scale   = options[:scale] if options.include?(:scale)
           end
         end
       end
@@ -467,6 +491,7 @@ module ActiveRecord
 
               @definition.column(column_name, column.type,
                 :limit => column.limit, :default => column.default,
+                :precision => column.precision, :scale => column.scale,
                 :null => column.null)
             end
             @definition.primary_key(primary_key(from)) if primary_key(from)