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HDFS, mail # user - Is append allowed in HDFS?


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Re: Is append allowed in HDFS?
Harsh J 2012-04-09, 12:57
Inder,

Yes, that is a requirement for readers of sync-ing data. The new meta
entries can only be read by new readers. The read code would end up
being exactly like the implementation for method "fs -tail" at
http://svn.apache.org/viewvc/hadoop/common/branches/branch-1/src/core/org/apache/hadoop/fs/FsShell.java?view=markup
(Line 1101)

HBase does not read the WAL (HLog) continuously/vigorously as it
syncs, by the way. It only reads the them when a specific request is
made (for splitting, replaying and debug-printing).

On Mon, Apr 9, 2012 at 6:05 PM, Inder Pall <[EMAIL PROTECTED]> wrote:
> Based on what i have tried, after a sync you need to open a new Reader.
> Please correct if that's not the write semantics.
>
> Thanks,
> - Inder
>
>
> On Mon, Apr 9, 2012 at 4:23 PM, Harsh J <[EMAIL PROTECTED]> wrote:
>>
>> I'd also like to note that there are some unresolved issues with the
>> append version in the 1.x (stable) line.
>>
>> Note that HBase's use of the 0.20-append branch features are limited
>> to using "sync" calls alone (Described in p68 "Coherency Model",
>> Chapter 3 (The Hadoop Distributed File System) in Hadoop: The
>> Definitive Guide, 2nd Edition (O'Reilly)). Not the file-reopening
>> "append" calls. The latter is what is still with issues in the 1.x
>> releases today. Using the former is alright if its done in the way
>> similar to HBase's WAL (HLog) (or for similar needs).
>>
>> On Mon, Apr 9, 2012 at 3:45 PM, Ioan Eugen Stan <[EMAIL PROTECTED]>
>> wrote:
>> > 2012/4/7 Florin P <[EMAIL PROTECTED]>:
>> >> Hello!
>> >>   Just google it for supporting of append into HDFS files and the
>> >> result:
>> >> I'm puzzled. Can someone say: YES you can append in TextFile or
>> >> SequenceFile
>> >> or whatever format. If yes, in which version this feature is supported
>> >> ?
>> >> Also where can I find a good example of using the API? I know that is a
>> >> long
>> >> debate about this subject, but really it is challenge to find on the
>> >> google
>> >> the current status of this feature.
>> >> I look forward for a trust source answer.
>> >> Thank you,
>> >>   Regards,
>> >>    Florin
>> >
>> > Hi Florian,
>> >
>> > HDFS supports append in Hadoop 1.0.x branch and also 0.22 (a.k.a
>> > hadoop 2.x branch) and 0.23 (a.k.a hadoop 3.x branch).
>> >
>> > [1] http://hbase.apache.org/book/hadoop.html
>> > [2] http://hbase.apache.org/book/hadoop.html -- search for append in
>> > release notes
>> >
>> > Cheers,
>> > --
>> > Ioan Eugen Stan
>> > http://ieugen.blogspot.com/
>>
>>
>>
>> --
>> Harsh J
>
>
>
>
> --
> Thanks,
> - Inder
>   Tech Platforms @Inmobi
>   Linkedin - http://goo.gl/eR4Ub

--
Harsh J