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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6109) let sync_file_range() system call run in backgroud
Date Mon, 17 Mar 2014 20:44:45 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6109?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13938356#comment-13938356
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Colin Patrick McCabe commented on HDFS-6109:
--------------------------------------------

If the call to {{sync_file_range}} becomes asynchronous, then it can fall arbitrarily behind
over time.  This will get rid of one of the advantages of {{sync_file_range}}, which is that
it makes performance more predictable.  So I think if we do this, it should be optional.

> let sync_file_range() system call run in backgroud
> --------------------------------------------------
>
>                 Key: HDFS-6109
>                 URL: https://issues.apache.org/jira/browse/HDFS-6109
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: datanode
>    Affects Versions: 3.0.0, 2.3.0
>            Reporter: Liang Xie
>            Assignee: Liang Xie
>
> Through we passed SYNC_FILE_RANGE_WRITE to sync_file_range, to make it as asynchronous
as possible, it still could be blocked, e.g. the os io request queue is full.
> Since we use sync_file_range just as a page cache advisor role:) it doesn't decide or
guarantee the real durability, it would be nice if we could run it in  backgroud. At least
my test log showed, a few sync_file_range calls still cost tens of ms or more, due to the
happened location is in the critical write path(BlockReceiver class), from a upper view, like
HBase application, will "hung" tens of ms as well during Hlog syncing.
> Generally speaking, the patch could not improve too much, but, better than before, right
? :)



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