MAPREDUCE-6237. Multiple mappers with DBInputFormat don't work because of reusing conections. Contributed by Kannan Rajah.

hadoop-mapreduce-project/CHANGES.txt

@@ -346,6 +346,21 @@ Release 2.7.0 - UNRELEASED
     MAPREDUCE-6233. org.apache.hadoop.mapreduce.TestLargeSort.testLargeSort
     failed in trunk (zxu via rkanter)
 
+Release 2.6.1 - UNRELEASED
+
+  INCOMPATIBLE CHANGES
+
+  NEW FEATURES
+
+  IMPROVEMENTS
+
+  OPTIMIZATIONS
+
+  BUG FIXES
+
+    MAPREDUCE-6237. Multiple mappers with DBInputFormat don't work because of
+    reusing conections. (Kannan Rajah via ozawa)
+
 Release 2.6.0 - 2014-11-18
 
   INCOMPATIBLE CHANGES

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/lib/db/DBInputFormat.java

@@ -159,7 +159,7 @@ public void setConf(Configuration conf) {
     dbConf = new DBConfiguration(conf);
 
     try {
-      getConnection();
+      this.connection = createConnection();
 
       DatabaseMetaData dbMeta = connection.getMetaData();
       this.dbProductName = dbMeta.getDatabaseProductName().toUpperCase();
@@ -182,18 +182,25 @@ public DBConfiguration getDBConf() {
   }
 
   public Connection getConnection() {
+    // TODO Remove this code that handles backward compatibility.
+    if (this.connection == null) {
+      this.connection = createConnection();
+    }
+
+    return this.connection;
+  }
+
+  public Connection createConnection() {
     try {
-      if (null == this.connection) {
+      Connection newConnection = dbConf.getConnection();
-        // The connection was closed; reinstantiate it.
+      newConnection.setAutoCommit(false);
-        this.connection = dbConf.getConnection();
+      newConnection.setTransactionIsolation(
-        this.connection.setAutoCommit(false);
+          Connection.TRANSACTION_SERIALIZABLE);
-        this.connection.setTransactionIsolation(
+
-            Connection.TRANSACTION_SERIALIZABLE);
+      return newConnection;
-      }
     } catch (Exception e) {
       throw new RuntimeException(e);
     }
-    return connection;
   }
 
   public String getDBProductName() {
@@ -210,17 +217,17 @@ protected RecordReader<LongWritable, T> createDBRecordReader(DBInputSplit split,
       if (dbProductName.startsWith("ORACLE")) {
         // use Oracle-specific db reader.
         return new OracleDBRecordReader<T>(split, inputClass,
-            conf, getConnection(), getDBConf(), conditions, fieldNames,
+            conf, createConnection(), getDBConf(), conditions, fieldNames,
             tableName);
       } else if (dbProductName.startsWith("MYSQL")) {
         // use MySQL-specific db reader.
         return new MySQLDBRecordReader<T>(split, inputClass,
-            conf, getConnection(), getDBConf(), conditions, fieldNames,
+            conf, createConnection(), getDBConf(), conditions, fieldNames,
             tableName);
       } else {
         // Generic reader.
         return new DBRecordReader<T>(split, inputClass,
-            conf, getConnection(), getDBConf(), conditions, fieldNames,
+            conf, createConnection(), getDBConf(), conditions, fieldNames,
             tableName);
       }
     } catch (SQLException ex) {

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/lib/db/DataDrivenDBInputFormat.java

@@ -178,7 +178,6 @@ public List<InputSplit> getSplits(JobContext job) throws IOException {
 
     ResultSet results = null;
     Statement statement = null;
-    Connection connection = getConnection();
     try {
       statement = connection.createStatement();
 
@@ -289,12 +288,12 @@ protected RecordReader<LongWritable, T> createDBRecordReader(DBInputSplit split,
       if (dbProductName.startsWith("MYSQL")) {
         // use MySQL-specific db reader.
         return new MySQLDataDrivenDBRecordReader<T>(split, inputClass,
-            conf, getConnection(), dbConf, dbConf.getInputConditions(),
+            conf, createConnection(), dbConf, dbConf.getInputConditions(),
             dbConf.getInputFieldNames(), dbConf.getInputTableName());
       } else {
         // Generic reader.
         return new DataDrivenDBRecordReader<T>(split, inputClass,
-            conf, getConnection(), dbConf, dbConf.getInputConditions(),
+            conf, createConnection(), dbConf, dbConf.getInputConditions(),
             dbConf.getInputFieldNames(), dbConf.getInputTableName(),
             dbProductName);
       }

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/lib/db/OracleDataDrivenDBInputFormat.java

@@ -84,7 +84,7 @@ protected RecordReader<LongWritable, T> createDBRecordReader(DBInputSplit split,
     try {
       // Use Oracle-specific db reader
       return new OracleDataDrivenDBRecordReader<T>(split, inputClass,
-          conf, getConnection(), dbConf, dbConf.getInputConditions(),
+          conf, createConnection(), dbConf, dbConf.getInputConditions(),
           dbConf.getInputFieldNames(), dbConf.getInputTableName());
     } catch (SQLException ex) {
       throw new IOException(ex.getMessage());