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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6109) let sync_file_range() system call run in background
Date Mon, 26 May 2014 21:04:02 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6109?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14009079#comment-14009079

stack commented on HDFS-6109:

Thanks for the blog post pointer. Pertinent.

Nit: Swap ofer on this if/else +          if (!syncBehindWritesInBackground) {   It is harder
to read NOT true.

Its a big of a pain running a pool of threads just to do sync_file_range (that is supposed
to be able to run asynchronously -- except it often doesn't as per the blog posting) but this
is better than our having big pauses.

+1 on patch.  This facility is off by default and doesn't cost when off.  A test that verifies
the executor runs and calls sync_file_range when this facility is enabled would be a little
pedantic IMO.  What do others think?

Nice one [~xieliang007]

> let sync_file_range() system call run in background
> ---------------------------------------------------
>                 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
>         Attachments: HDFS-6109.txt
> 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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