hadoop-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Azuryy Yu <azury...@gmail.com>
Subject Re: copy chunk of hadoop output
Date Sat, 02 Mar 2013 00:38:27 GMT
yes,just ignore this log.
On Mar 2, 2013 7:27 AM, "jamal sasha" <jamalshasha@gmail.com> wrote:

> Though it copies.. but it gives this error?
>
>
> On Fri, Mar 1, 2013 at 3:21 PM, jamal sasha <jamalshasha@gmail.com> 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 <harsh@cloudera.com> 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
>>> <jean-marc@spaggiari.org> 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 <harsh@cloudera.com>:
>>> >> 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
>>> >> <jean-marc@spaggiari.org> 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 <jamalshasha@gmail.com>:
>>> >>>> Awesome thanks :)
>>> >>>>
>>> >>>>
>>> >>>> On Tue, Feb 19, 2013 at 2:14 PM, Harsh J <harsh@cloudera.com>
>>> wrote:
>>> >>>>
>>> >>>>> You can instead use 'fs -cat' and the 'head' coreutil, as
one
>>> example:
>>> >>>>>
>>> >>>>> hadoop fs -cat 100-byte-dfs-file | head -c 5 > 5-byte-local-file
>>> >>>>>
>>> >>>>> On Wed, Feb 20, 2013 at 3:38 AM, jamal sasha <
>>> jamalshasha@gmail.com>
>>> >>>>> wrote:
>>> >>>>> > Hi,
>>> >>>>> >   I was wondering in the following command:
>>> >>>>> >
>>> >>>>> > bin/hadoop dfs -copyToLocal hdfspath localpath
>>> >>>>> > can we have specify to copy not full but like xMB's
of file to
>>> local
>>> >>>>> drive?
>>> >>>>> >
>>> >>>>> > Is something like this possible
>>> >>>>> > Thanks
>>> >>>>> > Jamal
>>> >>>>>
>>> >>>>>
>>> >>>>>
>>> >>>>> --
>>> >>>>> Harsh J
>>> >>>>>
>>> >>>>
>>> >>
>>> >>
>>> >>
>>> >> --
>>> >> Harsh J
>>> >>
>>>
>>>
>>>
>>> --
>>> Harsh J
>>>
>>
>>
>

Mime
View raw message