Github user MLnick commented on the pull request:
https://github.com/apache/spark/pull/1338#issuecomment-50068945
Ok I've been through it in detail and everything looks good, with the
exception of one issue that I picked up. The saving currently inherently
assumes that the `serializer` on the `PythonRDD` is `PickleSerializer`. If this
is not the case for whatever reason then it will fail.
This happens for `RDD`s created from `cartesian` and `zip`:
```python
In [1]: rdd = sc.parallelize(range(10))
In [2]: cart = rdd.cartesian(rdd)
In [3]: cart.saveAsSequenceFile("/tmp/cart.sf")
---------------------------------------------------------------------------
Py4JError Traceback (most recent call last)
<ipython-input-3-06070310df19> in <module>()
----> 1 cart.saveAsSequenceFile("/tmp/cart.sf")
...
Py4JError: An error occurred while calling
z:org.apache.spark.api.python.PythonRDD.saveAsSequenceFile. Trace:
py4j.Py4JException: Method saveAsSequenceFile([class
org.apache.spark.api.java.JavaPairRDD, class java.lang.String, null]) does not
exist
at py4j.reflection.ReflectionEngine.getMethod(ReflectionEngine.java:333)
at py4j.reflection.ReflectionEngine.getMethod(ReflectionEngine.java:358)
at py4j.Gateway.invoke(Gateway.java:254)
at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:132)
at py4j.commands.CallCommand.execute(CallCommand.java:79)
at py4j.GatewayConnection.run(GatewayConnection.java:207)
at java.lang.Thread.run(Thread.java:745)
In [4]: x = sc.parallelize(range(0,5))
In [5]: y = sc.parallelize(range(1000, 1005))
In [6]: x.zip(y).saveAsSequenceFile("/tmp/zip.sf")
---------------------------------------------------------------------------
Py4JError Traceback (most recent call last)
<ipython-input-6-ad82cb2565a3> in <module>()
----> 1 x.zip(y).saveAsSequenceFile("/tmp/zip.sf")
...
/Users/Nick/workspace/scala/spark/python/lib/py4j-0.8.1-src.zip/py4j/protocol.py
in get_return_value(answer, gateway_client, target_id, name)
302 raise Py4JError(
303 'An error occurred while calling {0}{1}{2}.
Trace:\n{3}\n'.
--> 304 format(target_id, '.', name, value))
305 else:
306 raise Py4JError(
Py4JError: An error occurred while calling
z:org.apache.spark.api.python.PythonRDD.saveAsSequenceFile. Trace:
py4j.Py4JException: Method saveAsSequenceFile([class
org.apache.spark.api.java.JavaPairRDD, class java.lang.String, null]) does not
exist
at py4j.reflection.ReflectionEngine.getMethod(ReflectionEngine.java:333)
at py4j.reflection.ReflectionEngine.getMethod(ReflectionEngine.java:358)
at py4j.Gateway.invoke(Gateway.java:254)
at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:132)
at py4j.commands.CallCommand.execute(CallCommand.java:79)
at py4j.GatewayConnection.run(GatewayConnection.java:207)
at java.lang.Thread.run(Thread.java:745)
```
The fix is simple - use what `saveAsPickleFile` does:
```python
self._reserialize(BatchedSerializer(PickleSerializer(), batchSize))._jrdd
```
I confirmed that something like the following works in `saveAsSequenceFile`:
```python
reser_rdd = self._reserialize(BatchedSerializer(PickleSerializer(),
batchSize))._jrdd
self.ctx._jvm.PythonRDD.saveAsSequenceFile(reser_rdd, path,
compressionCodecClass)
```
Apart from this I think this looks good for merge, subject to @mateiz call
on the covariance point.
@kanzhang would be great to try get this finalised for merge window
tomorrow. Sorry for the delay on my side!
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