[jira] [Commented] (HADOOP-18184) s3a prefetching stream to support unbuffer()

["Steve Loughran (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-18184?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17513524#comment-17513524 ] 

Steve Loughran commented on HADOOP-18184:
-----------------------------------------

the same streamStatistics reference needs to be preserved across unbuffer/read sequences; 

> 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
>            Priority: Major
>
> 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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