Add auto reconnect support utilizing a new #with_auto_reconnect block…

…. By default each query run through the adapter will automatically reconnect at standard intervals, logging attempts along the way, till success or the original exception bubbles up. See docs for more details. Resolves ticket rails-sqlserver#18 http://rails-sqlserver.lighthouseapp.com/projects/20277/tickets/18-sql-server-adapter-doesnt-reconnect-on-lost-connection

CHANGELOG

@@ -1,6 +1,10 @@
 
 MASTER
 
+* Add auto reconnect support utilizing a new #with_auto_reconnect block. By default each query run through 
+  the adapter will automatically reconnect at standard intervals, logging attempts along the way, till success 
+  or the original exception bubbles up. See docs for more details. Resolves ticket #18 [Ken Collins] 
+
 * Update internal helper method #orders_and_dirs_set to cope with an order clause like "description desc". This 
   resolves ticket #26 [Ken Collins]
 

README.rdoc

@@ -16,6 +16,8 @@ The SQL Server adapter for rails is back for ActiveRecord 2.2 and up! We are cur
 * Enabled #case_sensitive_equality_operator used by unique validations.
 * Unicode character support for nchar, nvarchar and ntext data types. Configuration option for defaulting all string data types to the unicode safe types.
 * View support for table names, identity inserts, and column defaults.
+* A block method to run queries within a specific isolation level.
+* Automatically reconnects to lost database connections.
 
 ==== Date/Time Data Type Hinting
 
@@ -103,6 +105,12 @@ By default all queries to the INFORMATION_SCHEMA table is silenced. If you think
 
   ActiveRecord::ConnectionAdapters::SQLServerAdapter.log_info_schema_queries = true
 
+==== Auto Connecting
+
+By default the adapter will auto connect to lost DB connections. For every query it will retry at intervals of 2, 4, 8, 16 and 32 seconds. During each retry it will callback out to ActiveRecord::Base.did_retry_sqlserver_connection(connection,count). When all retries fail, it will callback to ActiveRecord::Base.did_loose_sqlserver_connection(connection). Both implementations of these methods are to write to the rails logger, however, they make great override points for notifications like Hoptoad. If you want to disable automatic reconnections use the following in an initializer.
+
+  ActiveRecord::ConnectionAdapters::SQLServerAdapter.auto_connect = false
+
 
 == Versions
 

lib/active_record/connection_adapters/sqlserver_adapter.rb

@@ -23,9 +23,17 @@ def self.sqlserver_connection(config) #:nodoc:
         host      = config[:host] ? config[:host].to_s : 'localhost'
         driver_url = "DBI:ADO:Provider=SQLOLEDB;Data Source=#{host};Initial Catalog=#{database};User ID=#{username};Password=#{password};"
       end
-      conn = DBI.connect(driver_url, username, password)
-      conn["AutoCommit"] = true
-      ConnectionAdapters::SQLServerAdapter.new(conn, logger, [driver_url, username, password])
+      ConnectionAdapters::SQLServerAdapter.new(logger, [driver_url, username, password])
+    end
+
+    protected
+
+    def self.did_retry_sqlserver_connection(connection,count)
+      logger.info "CONNECTION RETRY: #{connection.class.name} retry ##{count}."
+    end
+
+    def self.did_loose_sqlserver_connection(connection)
+      logger.info "CONNECTION LOST: #{connection.class.name}"
     end
 
   end
@@ -155,8 +163,15 @@ class SQLServerAdapter < AbstractAdapter
       SUPPORTED_VERSIONS      = [2000,2005].freeze
       LIMITABLE_TYPES         = ['string','integer','float','char','nchar','varchar','nvarchar'].freeze
 
+      LOST_CONNECTION_EXCEPTIONS = [DBI::DatabaseError, DBI::InterfaceError]
+      LOST_CONNECTION_MESSAGES = [
+        'Communication link failure',
+        'Read from the server failed',
+        'Write to the server failed',
+        'Database connection was already closed']
+
       cattr_accessor :native_text_database_type, :native_binary_database_type, :native_string_database_type,
-                     :log_info_schema_queries, :enable_default_unicode_types
+                     :log_info_schema_queries, :enable_default_unicode_types, :auto_connect
 
       class << self
 
@@ -166,9 +181,10 @@ def type_limitable?(type)
 
       end
 
-      def initialize(connection, logger, connection_options=nil)
-        super(connection, logger)
+      def initialize(logger, connection_options)
         @connection_options = connection_options
+        connect
+        super(raw_connection, logger)
         initialize_sqlserver_caches
         unless SUPPORTED_VERSIONS.include?(database_year)
           raise NotImplementedError, "Currently, only #{SUPPORTED_VERSIONS.to_sentence} are supported."
@@ -221,6 +237,10 @@ def inspect
         "#<#{self.class} version: #{version}, year: #{database_year}, connection_options: #{@connection_options.inspect}>"
       end
 
+      def auto_connect
+        @@auto_connect.is_a?(FalseClass) ? false : true
+      end
+
       def native_string_database_type
         @@native_string_database_type || (enable_default_unicode_types ? 'nvarchar' : 'varchar') 
       end
@@ -302,16 +322,14 @@ def disable_referential_integrity(&block)
       def active?
         raw_connection.execute("SELECT 1").finish
         true
-      rescue DBI::DatabaseError, DBI::InterfaceError
+      rescue *LOST_CONNECTION_EXCEPTIONS
         false
       end
 
       def reconnect!
         disconnect!
-        @connection = DBI.connect(*@connection_options)
-      rescue DBI::DatabaseError => e
-        @logger.warn "#{adapter_name} reconnection failed: #{e.message}" if @logger
-        false
+        connect
+        active?
       end
 
       def disconnect!
@@ -721,6 +739,47 @@ def remove_database_connections_and_rollback(name)
 
       protected
 
+      # CONNECTION MANAGEMENT ====================================#
+
+      def connect
+        driver_url, username, password = @connection_options
+        @connection = DBI.connect(driver_url, username, password)
+        configure_connection
+      rescue
+        raise unless @auto_connecting
+      end
+
+      def configure_connection
+        raw_connection['AutoCommit'] = true
+      end
+
+      def with_auto_reconnect
+        begin
+          yield
+        rescue *LOST_CONNECTION_EXCEPTIONS => e
+          if LOST_CONNECTION_MESSAGES.any? { |lcm| e.message =~ Regexp.new(lcm,Regexp::IGNORECASE) }
+            retry if auto_reconnected?
+          end
+          raise
+        end
+      end
+
+      def auto_reconnected?
+        return false unless auto_connect
+        @auto_connecting = true
+        count = 0
+        while count <= 5
+          sleep 2** count
+          ActiveRecord::Base.did_retry_sqlserver_connection(self,count)
+          return true if connect && active?
+          count += 1
+        end
+        ActiveRecord::Base.did_loose_sqlserver_connection(self)
+        false
+      ensure
+        @auto_connecting = false
+      end
+
       # DATABASE STATEMENTS ======================================
 
       def select(sql, name = nil, ignore_special_columns = false)
@@ -751,9 +810,9 @@ def info_schema_query
       def raw_execute(sql, name = nil, &block)
         log(sql, name) do
           if block_given?
-            raw_connection.execute(sql) { |handle| yield(handle) }
+            with_auto_reconnect { raw_connection.execute(sql) { |handle| yield(handle) } }
           else
-            raw_connection.execute(sql)
+            with_auto_reconnect { raw_connection.execute(sql) }
           end
         end
       end
@@ -767,7 +826,7 @@ def without_type_conversion
 
       def do_execute(sql,name=nil)
         log(sql, name || 'EXECUTE') do
-          raw_connection.do(sql)
+          with_auto_reconnect { raw_connection.do(sql) }
         end
       end
 

test/cases/connection_test_sqlserver.rb

@@ -78,6 +78,37 @@ def setup
     end
   end
 
+  context 'Connection management' do
+
+    setup do
+      assert @connection.active?
+    end
+
+    should 'be able to disconnect and reconnect at will' do
+      @connection.disconnect!
+      assert !@connection.active?
+      @connection.reconnect!
+      assert @connection.active?
+    end
+
+    should 'auto reconnect when setting is on' do
+      with_auto_connect(true) do
+        @connection.disconnect!
+        assert_nothing_raised() { Topic.count }
+        assert @connection.active?
+      end
+    end
+
+    should 'not auto reconnect when setting is off' do
+      with_auto_connect(false) do
+        @connection.disconnect!
+        assert_raise(ActiveRecord::StatementInvalid) { Topic.count }
+      end
+    end
+
+  end
+
+
 
   private
 
@@ -99,5 +130,13 @@ def assert_all_statements_used_are_closed(&block)
   ensure
     GC.enable
   end
+
+  def with_auto_connect(boolean)
+    existing = ActiveRecord::ConnectionAdapters::SQLServerAdapter.auto_connect
+    ActiveRecord::ConnectionAdapters::SQLServerAdapter.auto_connect = boolean
+    yield
+  ensure
+    ActiveRecord::ConnectionAdapters::SQLServerAdapter.auto_connect = existing
+  end
 
 end