prevent mysql driver from pulling entire resultset into memory. explicitly close resultset and statement.

core/src/main/scala/spark/rdd/JdbcRDD.scala

@@ -15,7 +15,7 @@ import spark.util.NextIterator
   @param lowerBound the minimum value of the first placeholder
   @param upperBound the maximum value of the second placeholder
     The lower and upper bounds are inclusive.
-  @param numPartitions the amount of parallelism.
+  @param numPartitions the number of partitions.
     Given a lowerBound of 1, an upperBound of 20, and a numPartitions of 2,
     the query would be executed twice, once with (1, 10) and once with (11, 20)
   @param mapRow a function from a ResultSet to a single row of the desired result type(s).
@@ -40,10 +40,15 @@ class JdbcRDD[T: ClassManifest](
       toArray
 
   override def compute(thePart: Partition, context: TaskContext) = new NextIterator[T] {
+    context.addOnCompleteCallback{ () => closeIfNeeded() }
     val part = thePart.asInstanceOf[JdbcPartition]
     val conn = getConnection()
-    context.addOnCompleteCallback{ () => closeIfNeeded() }
+    val stmt = conn.prepareStatement(sql, ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY)
-    val stmt = conn.prepareStatement(sql)
+    // force mysql driver to stream rather than pull entire resultset into memory
+    if (conn.getMetaData.getURL.matches("jdbc:mysql:.*")) {
+      stmt.setFetchSize(Integer.MIN_VALUE)
+      logInfo("statement fetch size set to: " + stmt.getFetchSize + " to force MySQL streaming ")
+    }
     stmt.setLong(1, part.lower)
     stmt.setLong(2, part.upper)
     val rs = stmt.executeQuery()
@@ -59,8 +64,18 @@ class JdbcRDD[T: ClassManifest](
 
     override def close() {
       try {
-        logInfo("closing connection")
+        if (null != rs && ! rs.isClosed()) rs.close()
-        conn.close()
+      } catch {
+        case e: Exception => logWarning("Exception closing resultset", e)
+      }
+      try {
+        if (null != stmt && ! stmt.isClosed()) stmt.close()
+      } catch {
+        case e: Exception => logWarning("Exception closing statement", e)
+      }
+      try {
+        if (null != conn && ! stmt.isClosed()) conn.close()
+        logInfo("closed connection")
       } catch {
         case e: Exception => logWarning("Exception closing connection", e)
       }