[jira] [Commented] (SPARK-16262) Impossible to remake new SparkContext using SparkSession API in Pyspark

["Vladimir Feinberg (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-16262?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15353630#comment-15353630 ] 

Vladimir Feinberg commented on SPARK-16262:
-------------------------------------------

What do you mean by "clearing that variable"? Are you referring to setting {{SparkSession._instantiatedContext = None}}? The issue with that is that I definitely see a user wanting to change the configuration of a spark session within a single process, but I don't think it's reasonable to expect them to set a hidden variable to {{None}}. Based on another bug I opened (SPARK-16263), this seems to be a general issue with global context in the API.

> Impossible to remake new SparkContext using SparkSession API in Pyspark
> -----------------------------------------------------------------------
>
>                 Key: SPARK-16262
>                 URL: https://issues.apache.org/jira/browse/SPARK-16262
>             Project: Spark
>          Issue Type: Improvement
>          Components: PySpark
>            Reporter: Vladimir Feinberg
>            Priority: Minor
>
> There are multiple use cases where one might like to be able to stop and re-start a {{SparkSession}}: configuration changes or modular testing. The following code demonstrates that without clearing a hidden global {{SparkSession._instantiatedContext = None}} it is impossible to re-create a new Spark session after stopping one in the same process:
> {code}
> >>> from pyspark.sql import SparkSession
> >>> spark = SparkSession.builder.getOrCreate()
> Using Spark's default log4j profile: org/apache/spark/log4j-defaults.properties
> Setting default log level to "WARN".
> To adjust logging level use sc.setLogLevel(newLevel).
> 16/06/28 11:28:10 WARN NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
> 16/06/28 11:28:10 WARN Utils: Your hostname, vlad-databricks resolves to a loopback address: 127.0.1.1; using 192.168.3.166 instead (on interface enp0s31f6)
> 16/06/28 11:28:10 WARN Utils: Set SPARK_LOCAL_IP if you need to bind to another address
> >>> spark.stop()
> >>> spark = SparkSession.builder.getOrCreate()
> >>> spark.createDataFrame([(1,)])
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
>   File "pyspark/sql/session.py", line 514, in createDataFrame
>     rdd, schema = self._createFromLocal(map(prepare, data), schema)
>   File "pyspark/sql/session.py", line 394, in _createFromLocal
>     return self._sc.parallelize(data), schema
>   File "pyspark/context.py", line 410, in parallelize
>     numSlices = int(numSlices) if numSlices is not None else self.defaultParallelism
>   File "pyspark/context.py", line 346, in defaultParallelism
>     return self._jsc.sc().defaultParallelism()
> AttributeError: 'NoneType' object has no attribute 'sc'
> {code}



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