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From Jim Kellerman <...@powerset.com>
Subject Re: [jira] Commented: (HADOOP-1700) Append to files in HDFS
Date Wed, 05 Sep 2007 05:46:25 GMT

On Tue, 2007-09-04 at 22:38 -0700, eric baldeschwieler (JIRA) wrote:
>     [ https://issues.apache.org/jira/browse/HADOOP-1700?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12524988
> eric baldeschwieler commented on HADOOP-1700:
> ---------------------------------------------
> Just wanted to pitch in some context...
> Jim stated in the opening of this bug that a single client writing would be enough to
address this issue.  I agree.  But what we should be clearer about is the ultimate desired
semantics for readers.  I'd define success as having a single client doing appends and flushes
as desired (say per line in a log file) and having multiple clients "tail -f" the file and
see updates at a reasonable rate, IE soon after each flush or every 64k bytes or so with less
than a seconds latency.
> This would let us build systems that log directly into HDFS and have related systems
respond based on those log streams.
> This is where I'd like to see us get with this issue.  Clearly getting there involves
getting a handle on all the stuff already discussed in this thread.  We also need to think
carefully about the pipelining and protocol issues involved in making this work.
> We might want to break the protocol change issues into another discussion, but I want
to make sure we don't converge on solutions that will not work considering fine grained "flushes".
> > Append to files in HDFS
> > -----------------------
> >
> >                 Key: HADOOP-1700
> >                 URL: https://issues.apache.org/jira/browse/HADOOP-1700
> >             Project: Hadoop
> >          Issue Type: New Feature
> >          Components: dfs
> >            Reporter: stack
> >
> > Request for being able to append to files in HDFS has been raised a couple of times
on the list of late.   For one example, see http://www.nabble.com/HDFS%2C-appending-writes-status-tf3848237.html#a10916193.
 Other mail describes folks' workarounds because this feature is lacking: e.g. http://www.nabble.com/Loading-data-into-HDFS-tf4200003.html#a12039480
(Later on this thread, Jim Kellerman re-raises the HBase need of this feature).  HADOOP-337
'DFS files should be appendable' makes mention of file append but it was opened early in the
life of HDFS when the focus was more on implementing the basics rather than adding new features.
 Interest fizzled.  Because HADOOP-337 is also a bit of a grab-bag -- it includes truncation
and being able to concurrently read/write -- rather than try and breathe new life into HADOOP-337,
instead, here is a new issue focused on file append.  Ultimately, being able to do as the
google GFS paper describes -- having multiple concurrent clients 
 making 'Atomic Record Append' to a single file would be sweet but at least for a first cut
at this feature, IMO, a single client appending to a single HDFS file letting the application
manage the access would be sufficent.
Jim Kellerman, Senior Engineer; Powerset

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