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https://issues.apache.org/jira/browse/HADOOP-14965?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17489161#comment-17489161
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Yongjun Zhang commented on HADOOP-14965:
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Hi [[email protected]] ,
Thanks for the work here. We applied it and noticed significant S3 access
number increase, which is quite some extra cost. Wonder if we should introduce
a new mode for this instead of changing the default behavior of Normal. See
[https://linux.die.net/man/2/fadvise:]
ADV_NORMAL No special treatment.
FADV_RANDOM Expect page references in random order.
FADV_SEQUENTIAL Expect page references in sequential order.
Thanks.
> 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
> Affects Versions: 2.8.1
> Reporter: Steve Loughran
> Assignee: Steve Loughran
> Priority: Major
> Fix For: 3.1.0, 3.0.1
>
> Attachments: HADOOP-14965-001.patch, HADOOP-14965-002.patch,
> HADOOP-14965-003.patch, HADOOP-14965-004.patch
>
>
> 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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