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https://issues.apache.org/jira/browse/HADOOP-18184?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17743212#comment-17743212
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ASF GitHub Bot commented on HADOOP-18184:
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steveloughran commented on PR #5832:
URL: https://github.com/apache/hadoop/pull/5832#issuecomment-1636074815
Yes, this is a lot more than just unbuffer, but its the first time i've
really had the code in the IDE with me writing tests to use IOStats, context
iostats, waiting for tests to finish etc.
I have more to do which I will followup on different jiras. key: actually
support small block memory caching so you can use the stream without any disk
use. needed to switch to this everywhere.
> s3a prefetching stream to support unbuffer()
> --------------------------------------------
>
> Key: HADOOP-18184
> URL: https://issues.apache.org/jira/browse/HADOOP-18184
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: fs/s3
> Affects Versions: 3.4.0
> Reporter: Steve Loughran
> Assignee: Steve Loughran
> Priority: Minor
> Labels: pull-request-available
>
> Apache Impala uses unbuffer() to free up all client side resources held by a
> stream, so allowing it to have a map of available (path -> stream) objects,
> retained across queries.
> This saves on having to reopen the files, with the cost of HEAD checks etc.
> S3AInputStream just closes its http connection. here there is a lot more
> state to discard, but all memory and file storage must be freed.
> until this done, ITestS3AContractUnbuffer must skip when the prefetch stream
> is used.
> its notable that the other tests don't fail, even though the stream doesn't
> implement the interface; the graceful degradation handles that. it should
> fail if the test xml resource says the stream does it, but that the stream
> capabilities say it doesn't.
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