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MapReduce >> mail # user >> copy chunk of hadoop output


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jamal sasha 2013-02-19, 22:08
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Harsh J 2013-02-19, 22:14
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jamal sasha 2013-02-19, 22:16
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Jean-Marc Spaggiari 2013-02-20, 19:44
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Harsh J 2013-02-20, 20:21
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jamal sasha 2013-03-01, 23:21
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Re: copy chunk of hadoop output
Though it copies.. but it gives this error?
On Fri, Mar 1, 2013 at 3:21 PM, jamal sasha <[EMAIL PROTECTED]> wrote:

> When I try this.. I get an error
> cat: Unable to write to output stream.
>
> Are these permissions issue
> How do i resolve this?
> THanks
>
>
> On Wed, Feb 20, 2013 at 12:21 PM, Harsh J <[EMAIL PROTECTED]> wrote:
>
>> No problem JM, I was confused as well.
>>
>> AFAIK, there's no shell utility that can let you specify an offset #
>> of bytes to start off with (similar to skip in dd?), but that can be
>> done from the FS API.
>>
>> On Thu, Feb 21, 2013 at 1:14 AM, Jean-Marc Spaggiari
>> <[EMAIL PROTECTED]> wrote:
>> > Hi Harsh,
>> >
>> > My bad.
>> >
>> > I read the example quickly and I don't know why I tought you used tail
>> > and not head.
>> >
>> > head will work perfectly. But tail will not since it will need to read
>> > the entier file. My comment was for tail, not for head, and therefore
>> > not application to the example you gave.
>> >
>> >
>> > hadoop fs -cat 100-byte-dfs-file | tail -c 5 > 5-byte-local-file
>> >
>> > Will have to download the entire file.
>> >
>> > Is there a way to "jump" into a certain position in a file and "cat"
>> from there?
>> >
>> > JM
>> >
>> > 2013/2/20, Harsh J <[EMAIL PROTECTED]>:
>> >> Hi JM,
>> >>
>> >> I am not sure how "dangerous" it is, since we're using a pipe here,
>> >> and as you yourself note, it will only last as long as the last bytes
>> >> have been got and then terminate.
>> >>
>> >> The -cat process will terminate because the
>> >> process we're piping to will terminate first after it reaches its goal
>> >> of -c <N bytes>; so certainly the "-cat" program will not fetch the
>> >> whole file down but it may fetch a few bytes extra over communication
>> >> due to use of read buffers (the extra data won't be put into the target
>> >> file, and get discarded).
>> >>
>> >> We can try it out and observe the "clienttrace" logged
>> >> at the DN at the end of the -cat's read. Here's an example:
>> >>
>> >> I wrote a 1.6~ MB file into a file called "foo.jar", see "bytes"
>> >> below, its ~1.58 MB:
>> >>
>> >> 2013-02-20 23:55:19,777 INFO
>> >> org.apache.hadoop.hdfs.server.datanode.DataNode.clienttrace: src:
>> >> /127.0.0.1:58785, dest: /127.0.0.1:50010, bytes: 1658314, op:
>> >> HDFS_WRITE, cliID: DFSClient_NONMAPREDUCE_915204057_1, offset: 0,
>> >> srvID: DS-1092147940-192.168.2.1-50010-1349279636946, blockid:
>> >> BP-1461691939-192.168.2.1-1349279623549:blk_2568668834545125596_73870,
>> >> duration: 192289000
>> >>
>> >> I ran the command "hadoop fs -cat foo.jar | head -c 5 > foo.xml" to
>> >> store first 5 bytes onto a local file:
>> >>
>> >> Asserting that post command we get 5 bytes:
>> >> ➜  ~ wc -c foo.xml
>> >>        5 foo.xml
>> >>
>> >> Asserting that DN didn't IO-read the whole file, see the read op below
>> >> and its "bytes" parameter, its only about 193 KB, not the whole block
>> >> of 1.58 MB we wrote earlier:
>> >>
>> >> 2013-02-21 00:01:32,437 INFO
>> >> org.apache.hadoop.hdfs.server.datanode.DataNode.clienttrace: src:
>> >> /127.0.0.1:50010, dest: /127.0.0.1:58802, bytes: 198144, op:
>> >> HDFS_READ, cliID: DFSClient_NONMAPREDUCE_-1698829178_1, offset: 0,
>> >> srvID: DS-1092147940-192.168.2.1-50010-1349279636946, blockid:
>> >> BP-1461691939-192.168.2.1-1349279623549:blk_2568668834545125596_73870,
>> >> duration: 19207000
>> >>
>> >> I don't see how this is anymore dangerous than doing a
>> >> -copyToLocal/-get, which retrieves the whole file anyway?
>> >>
>> >> On Wed, Feb 20, 2013 at 9:25 PM, Jean-Marc Spaggiari
>> >> <[EMAIL PROTECTED]> wrote:
>> >>> But be careful.
>> >>>
>> >>> hadoop fs -cat will retrieve the entire file and last only when it
>> >>> will have retrieve the last bytes you are looking for.
>> >>>
>> >>> If your file is many GB big, it will take a lot of time for this
>> >>> command to complete and will put some pressure on your network.
>> >>>
>> >>> JM
>> >>>
>> >>> 2013/2/19, jamal sasha <[EMAIL PROTECTED]>:
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Azuryy Yu 2013-03-02, 00:38