distribute_reads.rb in distribute_reads-0.2.2

- old
+ new

@@ -27,16 +27,17 @@
 
   def self.lag(connection: nil)
     raise DistributeReads::Error, "Don't use outside distribute_reads" unless Thread.current[:distribute_reads]
 
     connection ||= ActiveRecord::Base.connection
-    if %w(PostgreSQL PostGIS).include?(connection.adapter_name)
-      replica_pool = connection.instance_variable_get(:@slave_pool)
-      if replica_pool && replica_pool.connections.size > 1
-        warn "[distribute_reads] Multiple replicas available, lag only reported for one"
-      end
 
+    replica_pool = connection.instance_variable_get(:@slave_pool)
+    if replica_pool && replica_pool.connections.size > 1
+      warn "[distribute_reads] Multiple replicas available, lag only reported for one"
+    end
+
+    if %w(PostgreSQL PostGIS).include?(connection.adapter_name)
       # cache the version number
       @server_version_num ||= {}
       cache_key = connection.pool.object_id
       @server_version_num[cache_key] ||= connection.execute("SHOW server_version_num").first["server_version_num"].to_i
 
@@ -51,9 +52,19 @@
         "SELECT CASE
           WHEN NOT pg_is_in_recovery() OR #{lag_condition} THEN 0
           ELSE EXTRACT (EPOCH FROM NOW() - pg_last_xact_replay_timestamp())
         END AS lag".squish
       ).first["lag"].to_f
+    elsif %w(MySQL Mysql2 Mysql2Spatial Mysql2Rgeo).include?(connection.adapter_name)
+      replica_value = Thread.current[:distribute_reads][:replica]
+      begin
+        # makara doesn't send SHOW queries to replica, so we must force it
+        Thread.current[:distribute_reads][:replica] = true
+        status = connection.exec_query("SHOW SLAVE STATUS").to_hash.first
+        status ? status["Seconds_Behind_Master"].to_f : 0.0
+      ensure
+        Thread.current[:distribute_reads][:replica] = replica_value
+      end
     else
       raise DistributeReads::Error, "Option not supported with this adapter"
     end
   end
 