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From "Jiang Xingbo (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-24552) Task attempt numbers are reused when stages are retried
Date Wed, 13 Jun 2018 21:44:00 GMT

    [ https://issues.apache.org/jira/browse/SPARK-24552?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16511695#comment-16511695
] 

Jiang Xingbo commented on SPARK-24552:
--------------------------------------

IIUC stageAttemptId + taskAttemptId shall probably define a unique task attempt, and it carries
enough information to know how many failed attempts you had previously.

> Task attempt numbers are reused when stages are retried
> -------------------------------------------------------
>
>                 Key: SPARK-24552
>                 URL: https://issues.apache.org/jira/browse/SPARK-24552
>             Project: Spark
>          Issue Type: Bug
>          Components: Spark Core
>    Affects Versions: 2.1.1
>            Reporter: Ryan Blue
>            Priority: Major
>
> When stages are retried due to shuffle failures, task attempt numbers are reused. This
causes a correctness bug in the v2 data sources write path.
> Data sources (both the original and v2) pass the task attempt to writers so that writers
can use the attempt number to track and clean up data from failed or speculative attempts.
In the v2 docs for DataWriterFactory, the attempt number's javadoc states that "Implementations
can use this attempt number to distinguish writers of different task attempts."
> When two attempts of a stage use the same (partition, attempt) pair, two tasks can create
the same data and attempt to commit. The commit coordinator prevents both from committing
and will abort the attempt that finishes last. When using the (partition, attempt) pair to
track data, the aborted task may delete data associated with the (partition, attempt) pair.
If that happens, the data for the task that committed is also deleted as well, which is a
correctness bug.
> For a concrete example, I have a data source that creates files in place named with {{part-<partition>-<attempt>-<uuid>.<format>}}.
Because these files are written in place, both tasks create the same file and the one that
is aborted deletes the file, leading to data corruption when the file is added to the table.



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