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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HADOOP-14965) s3a input stream "normal" fadvise mode to be adaptive
Date Thu, 19 Oct 2017 09:56:00 GMT
Steve Loughran created HADOOP-14965:

             Summary: 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
            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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