Steve Loughran created SPARK-23977:
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Summary: Add committer 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
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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