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From "Apache Spark (JIRA)" <>
Subject [jira] [Commented] (SPARK-23966) Refactoring all checkpoint file writing logic in a common interface
Date Wed, 11 Apr 2018 23:02:00 GMT


Apache Spark commented on SPARK-23966:

User 'tdas' has created a pull request for this issue:

> Refactoring all checkpoint file writing logic in a common interface
> -------------------------------------------------------------------
>                 Key: SPARK-23966
>                 URL:
>             Project: Spark
>          Issue Type: Improvement
>          Components: Structured Streaming
>    Affects Versions: 2.3.0
>            Reporter: Tathagata Das
>            Assignee: Tathagata Das
>            Priority: Major
> Checkpoint files (offset log files, state store files) in Structured Streaming must be
written atomically such that no partial files are generated (would break fault-tolerance guarantees).
Currently, there are 3 locations which try to do this individually, and in some cases, incorrectly.
>  # HDFSOffsetMetadataLog - This uses a FileManager interface to use any implementation
of `FileSystem` or `FileContext` APIs. It preferably loads `FileContext` implementation as
FileContext of HDFS has atomic renames.
>  # HDFSBackedStateStore (aka in-memory state store)
>  ## Writing a file - This uses FileSystem APIs only to perform a rename.
This is incorrect as rename is not atomic in HDFS FileSystem implementation.
>  ## Writing a snapshot file - Same as above.
> Current problems:
>  # State Store behavior is incorrect - 
>  # Inflexible - Some file systems provide mechanisms other than write-to-temp-file-and-rename
for writing atomically and more efficiently. For example, with S3 you can write directly to
the final file and it will be made visible only when the entire file is written and closed
correctly. Any failure can be made to terminate the writing without making any partial files
visible in S3. The current code does not abstract out this mechanism enough that it can be
> Solution:
>  # Introduce a common interface that all 3 cases above can use to write checkpoint files
>  # This interface must provide the necessary interfaces that allow customization of the
write-and-rename mechanism.

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