Description
To write files in parallel to an external storage system as in HDFS-12090, there are two approaches:
- 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.
- 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.
Attachments
Attachments
Issue Links
- causes
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HADOOP-16150 checksumFS doesn't wrap concat(): concatenated files don't have checksums
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- Resolved
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- Resolved
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- is depended upon by
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HADOOP-15576 S3A Multipart Uploader to work with S3Guard and encryption
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- Resolved
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- Resolved
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- is related to
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- Closed
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