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https://issues.apache.org/jira/browse/SPARK-26549?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Hyukjin Kwon resolved SPARK-26549.
----------------------------------
Resolution: Fixed
Fix Version/s: 3.0.0
Issue resolved by pull request 23470
[https://github.com/apache/spark/pull/23470]
> PySpark worker reuse take no effect for parallelize xrange
> ----------------------------------------------------------
>
> Key: SPARK-26549
> URL: https://issues.apache.org/jira/browse/SPARK-26549
> Project: Spark
> Issue Type: Bug
> Components: PySpark
> Affects Versions: 3.0.0
> Reporter: Yuanjian Li
> Assignee: Yuanjian Li
> Priority: Major
> Fix For: 3.0.0
>
>
> During [the follow-up
> work|https://github.com/apache/spark/pull/23435#issuecomment-451079886] for
> PySpark worker reuse scenario, we found that the worker reuse takes no effect
> for `sc.parallelize(xrange(...))`.
> It happened because of the specialize rdd.parallelize for xrange(SPARK-4398)
> generated data by xrange, which don't need to use the passed-in iterator. But
> this will break the end of stream checking in python worker and finally cause
> worker reuse takes no effect.
> Relative code block and more details listing below:
> Current specialize logic of xrange don't need the passed-in iterator,
> context.py:
> {code:java}
> if isinstance(c, xrange):
> ...
> def f(split, iterator):
> return xrange(getStart(split), getStart(split + 1), step)
> ...
> return self.parallelize([], numSlices).mapPartitionsWithIndex(f)
> {code}
> We got an unexpected value -1 which refers to END_OF_DATA_SECTION while check
> end of stream. See the code in worker.py:
> {code:java}
> # check end of stream
> if read_int(infile) == SpecialLengths.END_OF_STREAM:
> write_int(SpecialLengths.END_OF_STREAM, outfile)
> else:
> # write a different value to tell JVM to not reuse this worker
> write_int(SpecialLengths.END_OF_DATA_SECTION, outfile)
> sys.exit(-1)
> {code}
> The code works well for parallelize(range) because the END_OF_DATA_SECTION
> has been handled during load iterator from the socket stream, see the code in
> FramedSerializer:
> {code:java}
> def load_stream(self, stream):
> while True:
> try:
> yield self._read_with_length(stream)
> except EOFError:
> return
> ...
> def _read_with_length(self, stream):
> length = read_int(stream)
> if length == SpecialLengths.END_OF_DATA_SECTION:
> raise EOFError #END_OF_DATA_SECTION raised EOF here and catched in
> load_stream
> elif length == SpecialLengths.NULL:
> return None
> obj = stream.read(length)
> if len(obj) < length:
> raise EOFError
> return self.loads(obj)
> {code}
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