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https://issues.apache.org/jira/browse/HADOOP-16132?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16780886#comment-16780886
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Justin Uang commented on HADOOP-16132:
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Copying over the last comment from the github ticket since we will be
continuing the conversation here:
[[email protected]]
{quote}BTW, one little side effect of breaking up the reads: every GET is its
own HTTP request, so gets billed differently, and for SSE-KMS, possibly a
separate call to AWS:KMS. Nobody quite knows about the latter, we do know that
heavy random seek IO on a single tree in a bucket can trigger more throttling
than you'd expect
Anyway, maybe for random IO the strategy would be to have a notion of aligned
blocks, say 8 MB, the current block is cached as it is read in, so a backward
seek can often work from in memory; the stream could be doing a readahead of ,
say, the next 2+ blocks in parallel & then store them in a ring of cached
blocks ready for when they are used.
you've got me thinking now...
{quote}
> Support multipart download in S3AFileSystem
> -------------------------------------------
>
> Key: HADOOP-16132
> URL: https://issues.apache.org/jira/browse/HADOOP-16132
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: fs/s3
> Reporter: Justin Uang
> Priority: Major
> Attachments: HADOOP-16132.001.patch
>
>
> I noticed that I get 150MB/s when I use the AWS CLI
> {code:java}
> aws s3 cp s3://<bucket>/<key> - > /dev/null{code}
> vs 50MB/s when I use the S3AFileSystem
> {code:java}
> hadoop fs -cat s3://<bucket>/<key> > /dev/null{code}
> Looking into the AWS CLI code, it looks like the
> [download|https://github.com/boto/s3transfer/blob/ca0b708ea8a6a1213c6e21ca5a856e184f824334/s3transfer/download.py]
> logic is quite clever. It downloads the next couple parts in parallel using
> range requests, and then buffers them in memory in order to reorder them and
> expose a single contiguous stream. I translated the logic to Java and
> modified the S3AFileSystem to do similar things, and am able to achieve
> 150MB/s download speeds as well. It is mostly done but I have some things to
> clean up first. The PR is here:
> https://github.com/palantir/hadoop/pull/47/files
> It would be great to get some other eyes on it to see what we need to do to
> get it merged.
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