[HDFS-13186] [PROVIDED Phase 2] Multipart Uploader API

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 3.2.0
• Target Version/s: 3.2.0
• Hadoop Flags: Reviewed
• Assignee: Ewan Higgs
• Reporter: Ewan Higgs
• Created: 23/Feb/18 14:29
• Updated: 14/Mar/19 19:42
• Resolved: 17/Jun/18 18:55

Description

To write files in parallel to an external storage system as in HDFS-12090, there are two approaches:

1. Naive approach: use a single datanode per file that copies blocks locally as it streams data to the external service. This requires a copy for each block inside the HDFS system and then a copy for the block to be sent to the external system.
2. Better approach: Single point (e.g. Namenode or SPS style external client) and Datanodes coordinate in a multipart - multinode upload.

This system needs to work with multiple back ends and needs to coordinate across the network. So we propose an API that resembles the following:

public UploadHandle multipartInit(Path filePath) throws IOException;

public PartHandle multipartPutPart(InputStream inputStream,
    int partNumber, UploadHandle uploadId) throws IOException;

public void multipartComplete(Path filePath,
    List<Pair<Integer, PartHandle>> handles, 
    UploadHandle multipartUploadId) throws IOException;

Here, UploadHandle and PartHandle are opaque handlers in the vein of PathHandle so they can be serialized and deserialized in hadoop-hdfs project without knowledge of how to deserialize e.g. S3A's version of a UpoadHandle and PartHandle.

In an object store such as S3A, the implementation is straight forward. In the case of writing multipart/multinode to HDFS, we can write each block as a file part. The complete call will perform a concat on the blocks.

Issue Links

• causes: HADOOP-16150 checksumFS doesn't wrap concat(): concatenated files don't have checksums
• causes: HDFS-13707 [PROVIDED Storage] Fix failing integration tests in ITestProvidedImplementation
• is depended upon by: HADOOP-15576 S3A Multipart Uploader to work with S3Guard and encryption
• is depended upon by: HDFS-13713 Add specification of Multipart Upload API to FS specification, with contract tests
• is related to: HBASE-20431 Store commit transaction for filesystems that do not support an atomic rename