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From "Apache Spark (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-23977) Add commit protocol binding to Hadoop 3.1 PathOutputCommitter mechanism
Date Fri, 13 Apr 2018 13:18:00 GMT

    [ https://issues.apache.org/jira/browse/SPARK-23977?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16437288#comment-16437288
] 

Apache Spark commented on SPARK-23977:
--------------------------------------

User 'steveloughran' has created a pull request for this issue:
https://github.com/apache/spark/pull/21066

> Add commit protocol binding to Hadoop 3.1 PathOutputCommitter mechanism
> -----------------------------------------------------------------------
>
>                 Key: SPARK-23977
>                 URL: https://issues.apache.org/jira/browse/SPARK-23977
>             Project: Spark
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 2.4.0
>            Reporter: Steve Loughran
>            Priority: Minor
>
> Hadoop 3.1 adds a mechanism for job-specific and store-specific committers (MAPREDUCE-6823,
MAPREDUCE-6956), and one key implementation, S3A committers, HADOOP-13786
> These committers deliver high-performance output of MR and spark jobs to S3, and offer
the key semantics which Spark depends on: no visible output until job commit, a failure of
a task at an stage, including partway through task commit, can be handled by executing and
committing another task attempt. 
> In contrast, the FileOutputFormat commit algorithms on S3 have issues:
> * Awful performance because files are copied by rename
> * FileOutputFormat v1: weak task commit failure recovery semantics as the (v1) expectation:
"directory renames are atomic" doesn't hold.
> * S3 metadata eventual consistency can cause rename to miss files or fail entirely (SPARK-15849)
> Note also that FileOutputFormat "v2" commit algorithm doesn't offer any of the commit
semantics w.r.t observability of or recovery from task commit failure, on any filesystem.
> The S3A committers address these by way of uploading all data to the destination through
multipart uploads, uploads which are only completed in job commit.
> The new {{PathOutputCommitter}} factory mechanism allows applications to work with the
S3A committers and any other, by adding a plugin mechanism into the MRv2 FileOutputFormat
class, where it job config and filesystem configuration options can dynamically choose the
output committer.
> Spark can use these with some binding classes to 
> # Add a subclass of {{HadoopMapReduceCommitProtocol}} which uses the MRv2 classes and
{{PathOutputCommitterFactory}} to create the committers.
> # Add a {{BindingParquetOutputCommitter extends ParquetOutputCommitter}}
> to wire up Parquet output even when code requires the committer to be a subclass of {{ParquetOutputCommitter}}
> This patch builds on SPARK-23807 for setting up the dependencies.



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