added StreamingContext.remember

Author: giwa

python/pyspark/streaming/context.py

@@ -21,6 +21,7 @@
 from pyspark.serializers import PickleSerializer, BatchedSerializer, UTF8Deserializer
 from pyspark.context import SparkContext
 from pyspark.streaming.dstream import DStream
+from pyspark.streaming.duration import Duration
 
 from py4j.java_collections import ListConverter
 
@@ -107,6 +108,20 @@ def awaitTermination(self, timeout=None):
         else:
             self._jssc.awaitTermination(timeout)
 
+    def remember(self, duration):
+        """
+        Set each DStreams in this context to remember RDDs it generated in the last given duration.
+        DStreams remember RDDs only for a limited duration of time and releases them for garbage
+        collection. This method allows the developer to specify how to long to remember the RDDs (
+        if the developer wishes to query old data outside the DStream computation).
+        @param duration pyspark.streaming.duration.Duration object.
+               Minimum duration that each DStream should remember its RDDs
+        """
+        if not isinstance(duration, Duration):
+            raise TypeError("Input should be pyspark.streaming.duration.Duration object")
+
+        self._jssc.remember(duration._jduration)
+
     # TODO: add storageLevel
     def socketTextStream(self, hostname, port):
         """