Yuanjian Li created SPARK-26549:
-----------------------------------
Summary: PySpark worker reuse take no effect for Python3
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
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 Python3 while works properly for Python2 and PyPy.
It happened because, during the python worker check end of the stream in
Python3, we got an unexpected value -1 here which refers to
END_OF_DATA_SECTION. See the code in worker.py:
{code:python}
# 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 Python2 and PyPy cause the END_OF_DATA_SECTION has been
handled during load iterator from the socket stream, see the code in
FramedSerializer:
{code:python}
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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