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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1700) Append to files in HDFS
Date Thu, 06 Sep 2007 17:52:32 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1700?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12525483
] 

Doug Cutting commented on HADOOP-1700:
--------------------------------------

> sameer: [ ... ] but the corner cases when a client dies in the middle of a write could
be trickier to handle.

Yes, that worries me.  I'd be more comfortable sending a new version per flush, so that we
have some atomic ground to stand on.  Perhaps we can address clock skew by, as you suggest,
using revisions rather than timestamps.  The namenode need not be involved in the allocation
of each revision, only in initializing the revision counter for a modification sequence. 
After that, the DFSClient can increment the revision for each buffer.  Do we lose anything
by not using timestamps?  We could avoid collisions of blockid+revision with the filesystem
id, no?

> eric: the next logical step here is for us to outline a more detail proposal

Yep.  That'd be good.  +1

> 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.

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