MAPREDUCE-6357. MultipleOutputs.write() API should document that output committing is not utilized when input path is absolute. Contributed by Dustin Cote.

(cherry picked from commit 2ba90c93d71aa2d30ee9ed431750c10c685e5599)

hadoop-mapreduce-project/CHANGES.txt

@@ -286,6 +286,10 @@ Release 2.8.0 - UNRELEASED
     MAPREDUCE-5817. Mappers get rescheduled on node transition even after all
     reducers are completed. (Sangjin Lee via kasha)
 
+    MAPREDUCE-6357. MultipleOutputs.write() API should document that output
+    committing is not utilized when input path is absolute.
+    (Dustin Cote via aajisaka)
+
 Release 2.7.2 - UNRELEASED
 
   INCOMPATIBLE CHANGES

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/lib/output/MultipleOutputs.java

@@ -120,7 +120,11 @@ import java.util.*;
  * 
  * <p>
  * Use <code>MultipleOutputs.write(KEYOUT key, VALUEOUT value, String baseOutputPath)</code> to write key and 
- * value to a path specified by <code>baseOutputPath</code>, with no need to specify a named output:
+ * value to a path specified by <code>baseOutputPath</code>, with no need to specify a named output.
+ * <b>Warning</b>: when the baseOutputPath passed to MultipleOutputs.write
+ * is a path that resolves outside of the final job output directory, the
+ * directory is created immediately and then persists through subsequent
+ * task retries, breaking the concept of output committing:
  * </p>
  * 
  * <pre>
@@ -418,6 +422,10 @@ public class MultipleOutputs<KEYOUT, VALUEOUT> {
    * @param value          the value
    * @param baseOutputPath base-output path to write the record to.
    * Note: Framework will generate unique filename for the baseOutputPath
+   * <b>Warning</b>: when the baseOutputPath is a path that resolves
+   * outside of the final job output directory, the directory is created
+   * immediately and then persists through subsequent task retries, breaking
+   * the concept of output committing.
    */
   @SuppressWarnings("unchecked")
   public <K, V> void write(String namedOutput, K key, V value,
@@ -442,6 +450,10 @@ public class MultipleOutputs<KEYOUT, VALUEOUT> {
    * @param value     the value
    * @param baseOutputPath base-output path to write the record to.
    * Note: Framework will generate unique filename for the baseOutputPath
+   * <b>Warning</b>: when the baseOutputPath is a path that resolves
+   * outside of the final job output directory, the directory is created
+   * immediately and then persists through subsequent task retries, breaking
+   * the concept of output committing.
    */
   @SuppressWarnings("unchecked")
   public void write(KEYOUT key, VALUEOUT value, String baseOutputPath)