[SPARK-2024] Add saveAsSequenceFile to PySpark

JIRA issue: https://issues.apache.org/jira/browse/SPARK-2024

This PR is a followup to #455 and adds capabilities for saving PySpark RDDs using SequenceFile or any Hadoop OutputFormats.

* Added RDD methods ```saveAsSequenceFile```, ```saveAsHadoopFile``` and ```saveAsHadoopDataset```, for both old and new MapReduce APIs.

* Default converter for converting common data types to Writables. Users may specify custom converters to convert to desired data types.

* No out-of-box support for reading/writing arrays, since ArrayWritable itself doesn't have a no-arg constructor for creating an empty instance upon reading. Users need to provide ArrayWritable subtypes. Custom converters for converting arrays to suitable ArrayWritable subtypes are also needed when writing. When reading, the default converter will convert any custom ArrayWritable subtypes to ```Object[]``` and they get pickled to Python tuples.

* Added HBase and Cassandra output examples to show how custom output formats and converters can be used.

cc MLnick mateiz ahirreddy pwendell

Author: Kan Zhang <kzhang@apache.org>

Closes #1338 from kanzhang/SPARK-2024 and squashes the following commits:

c01e3ef [Kan Zhang] [SPARK-2024] code formatting
6591e37 [Kan Zhang] [SPARK-2024] renaming pickled -> pickledRDD
d998ad6 [Kan Zhang] [SPARK-2024] refectoring to get method params below 10
57a7a5e [Kan Zhang] [SPARK-2024] correcting typo
75ca5bd [Kan Zhang] [SPARK-2024] Better type checking for batch serialized RDD
0bdec55 [Kan Zhang] [SPARK-2024] Refactoring newly added tests
9f39ff4 [Kan Zhang] [SPARK-2024] Adding 2 saveAsHadoopDataset tests
0c134f3 [Kan Zhang] [SPARK-2024] Test refactoring and adding couple unbatched cases
7a176df [Kan Zhang] [SPARK-2024] Add saveAsSequenceFile to PySpark

1 files changed, 83 insertions, 0 deletions

diff --git a/examples/src/main/python/cassandra_outputformat.py b/examples/src/main/python/cassandra_outputformat.py
new file mode 100644
index 0000000000..1dfbf98604
--- /dev/null
+++ b/examples/src/main/python/cassandra_outputformat.py
@@ -0,0 +1,83 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+import sys
+
+from pyspark import SparkContext
+
+"""
+Create data in Cassandra fist
+(following: https://wiki.apache.org/cassandra/GettingStarted)
+
+cqlsh> CREATE KEYSPACE test
+   ... WITH REPLICATION = { 'class' : 'SimpleStrategy', 'replication_factor' : 1 };
+cqlsh> use test;
+cqlsh:test> CREATE TABLE users (
+        ...   user_id int PRIMARY KEY,
+        ...   fname text,
+        ...   lname text
+        ... );
+
+> cassandra_outputformat <host> test users 1745 john smith
+> cassandra_outputformat <host> test users 1744 john doe
+> cassandra_outputformat <host> test users 1746 john smith
+
+cqlsh:test> SELECT * FROM users;
+
+ user_id | fname | lname
+---------+-------+-------
+    1745 |  john | smith
+    1744 |  john |   doe
+    1746 |  john | smith
+"""
+if __name__ == "__main__":
+    if len(sys.argv) != 7:
+        print >> sys.stderr, """
+        Usage: cassandra_outputformat <host> <keyspace> <cf> <user_id> <fname> <lname>
+
+        Run with example jar:
+        ./bin/spark-submit --driver-class-path /path/to/example/jar /path/to/examples/cassandra_outputformat.py <args>
+        Assumes you have created the following table <cf> in Cassandra already,
+        running on <host>, in <keyspace>.
+
+        cqlsh:<keyspace>> CREATE TABLE <cf> (
+           ...   user_id int PRIMARY KEY,
+           ...   fname text,
+           ...   lname text
+           ... );
+        """
+        exit(-1)
+
+    host = sys.argv[1]
+    keyspace = sys.argv[2]
+    cf = sys.argv[3]
+    sc = SparkContext(appName="CassandraOutputFormat")
+
+    conf = {"cassandra.output.thrift.address":host,
+            "cassandra.output.thrift.port":"9160",
+            "cassandra.output.keyspace":keyspace,
+            "cassandra.output.partitioner.class":"Murmur3Partitioner",
+            "cassandra.output.cql":"UPDATE " + keyspace + "." + cf + " SET fname = ?, lname = ?",
+            "mapreduce.output.basename":cf,
+            "mapreduce.outputformat.class":"org.apache.cassandra.hadoop.cql3.CqlOutputFormat",
+            "mapreduce.job.output.key.class":"java.util.Map",
+            "mapreduce.job.output.value.class":"java.util.List"}
+    key = {"user_id" : int(sys.argv[4])}
+    sc.parallelize([(key, sys.argv[5:])]).saveAsNewAPIHadoopDataset(
+        conf=conf,
+        keyConverter="org.apache.spark.examples.pythonconverters.ToCassandraCQLKeyConverter",
+        valueConverter="org.apache.spark.examples.pythonconverters.ToCassandraCQLValueConverter")