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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1700) Append to files in HDFS
Date Wed, 05 Sep 2007 17:27:34 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1700?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12525165
] 

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

> sameer: solve the problem of detecting replicas from deleted files

Is that actually a problem?  We'll only generate such garbage blocks when nodes fail, and
only a few then, so it doesn't happen at that high of a rate, and the current blockreport
mechanism handles that.  Block versioning won't let us get rid of the blockreport mechanism,
so I still don't see that as an advantage of block versioning.  Am I missing something?

> eric: see updates at a reasonable rate, IE soon after each flush or every 64k bytes or
so with less than a seconds latency

That's a new requirement that I'd not heard before.  The mechanism I'd proposed would not
make appends visible until the file is closed, which is not what Eric's asking for.  So this
may make the case for block versioning.  If we really must support what Eric's asking, then
non-persistent timestamps on the blocks may be required.


> 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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