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Posted to dev@hive.apache.org by "Chao (JIRA)" <ji...@apache.org> on 2014/10/15 22:32:34 UTC
[jira] [Assigned] (HIVE-8457) MapOperator initialization fails when
multiple Spark threads is enabled [Spark Branch]
[ https://issues.apache.org/jira/browse/HIVE-8457?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Chao reassigned HIVE-8457:
--------------------------
Assignee: Chao
> MapOperator initialization fails when multiple Spark threads is enabled [Spark Branch]
> --------------------------------------------------------------------------------------
>
> Key: HIVE-8457
> URL: https://issues.apache.org/jira/browse/HIVE-8457
> Project: Hive
> Issue Type: Bug
> Components: Spark
> Reporter: Chao
> Assignee: Chao
>
> Currently, on the Spark branch, each thread it is bound with a thread-local IOContext, which gets initialized when we generates an input {{HadoopRDD}}, and later used in {{MapOperator}}, {{FilterOperator}}, etc.
> And, given the introduction of HIVE-8118, we may have multiple downstream RDDs that share the same input {{HadoopRDD}}, and we would like to have the {{HadoopRDD}} to be cached, to avoid scanning the same table multiple times. A typical case would be like the following:
> {noformat}
> inputRDD inputRDD
> | |
> MT_11 MT_12
> | |
> RT_1 RT_2
> {noformat}
> Here, {{MT_11}} and {{MT_12}} are {{MapTran}} from a splitted {{MapWork}},
> and {{RT_1}} and {{RT_2}} are two {{ReduceTran}}. Note that, this example is simplified, as we may also have {{ShuffleTran}} between {{MapTran}} and {{ReduceTran}}.
> When multiple Spark threads are running, {{MT_11}} may be executed first, and it will ask for an iterator from the {{HadoopRDD}} will trigger the creation of the iterator, which in turn triggers the initialization of the {{IOContext}} associated with that particular thread.
> *Now, the problem is*: before {{MT_12}} starts executing, it will also ask for an iterator from the
> {{HadoopRDD}}, and since the RDD is already cached, instead of creating a new iterator, it will just fetch it from the cached result. However, *this will skip the initialization of the IOContext associated with this particular thread*. And, when {{MT_12}} starts executing, it will try to initialize the {{MapOperator}}, but since the {{IOContext}} is not initialized, this will fail miserably.
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