Ewan Higgs created HDFS-13186:
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Summary: Multipart Multinode uploader API + Implementations
Key: HDFS-13186
URL: https://issues.apache.org/jira/browse/HDFS-13186
Project: Hadoop HDFS
Issue Type: Sub-task
Reporter: Ewan Higgs
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:
{code:java}
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;{code}
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.
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