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https://issues.apache.org/jira/browse/HADOOP-14965?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16214478#comment-16214478
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Rajesh Balamohan commented on HADOOP-14965:
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It would be good to tune itself based on the seek access patterns.
> s3a input stream "normal" fadvise mode to be adaptive
> -----------------------------------------------------
>
> Key: HADOOP-14965
> URL: https://issues.apache.org/jira/browse/HADOOP-14965
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: fs/s3
> Reporter: Steve Loughran
>
> HADOOP-14535 added seek optimisation to wasb, but rather than require the
> caller to declare sequential vs random, it works out for itself.
> # defaults to sequential, lazy seek
> # if the caller ever seeks backwards, switches to random IO.
> This means that on the use pattern of columnar stores: of go to end of file,
> read summary, then go to columns and work forwards, will switch to random IO
> after that first seek back (cost: one aborted HTTP connection)/.
> Where this should benefit the most is in downstream apps where you are
> working with different data sources in the same object store/running of the
> same app config, but have different read patterns. I'm seeing exactly this in
> some of my spark tests, where it's near impossible to set things up so that
> .gz files are read sequentially, but ORC data is read in random IO
> I propose the "normal" fadvise => adaptive, sequential==sequential always,
> random => random from the outset.
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