Home | About | Sematext search-lucene.com search-hadoop.com
NEW: Monitor These Apps!
elasticsearch, apache solr, apache hbase, hadoop, redis, casssandra, amazon cloudwatch, mysql, memcached, apache kafka, apache zookeeper, apache storm, ubuntu, centOS, red hat, debian, puppet labs, java, senseiDB
 Search Hadoop and all its subprojects:

Switch to Threaded View
HDFS >> mail # user >> Re: Hadoop noob question


Copy link to this message
-
Re: Hadoop noob question
Soon after replying I realized something else related to this.

Say we have a single file in HDFS (hdfs configured for default block size
64 MB) and the size of the file is 1 GB. Now if we use distcp to move it
from the current hdfs to another one , then
whether there would be any parallelism or just a single map task would be
fired?

As per what I have read , a mapper is launcher for a complete file or a set
of files. It doesn't operate at block level.So no parallelism even if the
file resides in HDFS.

Thanks,
Rahul
On Sun, May 12, 2013 at 6:28 PM, Rahul Bhattacharjee <
[EMAIL PROTECTED]> wrote:

> yeah you are right I mis read your earlier post.
>
> Thanks,
> Rahul
>
>
> On Sun, May 12, 2013 at 6:25 PM, Mohammad Tariq <[EMAIL PROTECTED]>wrote:
>
>> I had said that if you use distcp to copy data *from localFS to HDFS*then you won't be able to exploit parallelism as entire file is present on
>> a single machine. So no multiple TTs.
>>
>> Please comment if you think I am wring somewhere.
>>
>> Warm Regards,
>> Tariq
>> cloudfront.blogspot.com
>>
>>
>> On Sun, May 12, 2013 at 6:15 PM, Rahul Bhattacharjee <
>> [EMAIL PROTECTED]> wrote:
>>
>>> Yes , it's a MR job under the hood . my question was that you wrote that
>>> using distcp you loose the benefits  of parallel processing of Hadoop. I
>>> think the MR job of distcp divides files into individual map tasks based on
>>> the total size of the transfer , so multiple mappers would still be spawned
>>> if the size of transfer is huge and they would work in parallel.
>>>
>>> Correct me if there is anything wrong!
>>>
>>> Thanks,
>>> Rahul
>>>
>>>
>>> On Sun, May 12, 2013 at 6:07 PM, Mohammad Tariq <[EMAIL PROTECTED]>wrote:
>>>
>>>> No. distcp is actually a mapreduce job under the hood.
>>>>
>>>> Warm Regards,
>>>> Tariq
>>>> cloudfront.blogspot.com
>>>>
>>>>
>>>> On Sun, May 12, 2013 at 6:00 PM, Rahul Bhattacharjee <
>>>> [EMAIL PROTECTED]> wrote:
>>>>
>>>>> Thanks to both of you!
>>>>>
>>>>> Rahul
>>>>>
>>>>>
>>>>> On Sun, May 12, 2013 at 5:36 PM, Nitin Pawar <[EMAIL PROTECTED]>wrote:
>>>>>
>>>>>> you can do that using file:///
>>>>>>
>>>>>> example:
>>>>>>
>>>>>>
>>>>>> hadoop distcp hdfs://localhost:8020/somefile file:///Users/myhome/Desktop/
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Sun, May 12, 2013 at 5:23 PM, Rahul Bhattacharjee <
>>>>>> [EMAIL PROTECTED]> wrote:
>>>>>>
>>>>>>> @Tariq can you point me to some resource which shows how distcp is
>>>>>>> used to upload files from local to hdfs.
>>>>>>>
>>>>>>> isn't distcp a MR job ? wouldn't it need the data to be already
>>>>>>> present in the hadoop's fs?
>>>>>>>
>>>>>>>  Rahul
>>>>>>>
>>>>>>>
>>>>>>> On Sat, May 11, 2013 at 10:52 PM, Mohammad Tariq <[EMAIL PROTECTED]
>>>>>>> > wrote:
>>>>>>>
>>>>>>>> You'r welcome :)
>>>>>>>>
>>>>>>>> Warm Regards,
>>>>>>>> Tariq
>>>>>>>> cloudfront.blogspot.com
>>>>>>>>
>>>>>>>>
>>>>>>>> On Sat, May 11, 2013 at 10:46 PM, Rahul Bhattacharjee <
>>>>>>>> [EMAIL PROTECTED]> wrote:
>>>>>>>>
>>>>>>>>> Thanks Tariq!
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Sat, May 11, 2013 at 10:34 PM, Mohammad Tariq <
>>>>>>>>> [EMAIL PROTECTED]> wrote:
>>>>>>>>>
>>>>>>>>>> @Rahul : Yes. distcp can do that.
>>>>>>>>>>
>>>>>>>>>> And, bigger the files lesser the metadata hence lesser memory
>>>>>>>>>> consumption.
>>>>>>>>>>
>>>>>>>>>> Warm Regards,
>>>>>>>>>> Tariq
>>>>>>>>>> cloudfront.blogspot.com
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On Sat, May 11, 2013 at 9:40 PM, Rahul Bhattacharjee <
>>>>>>>>>> [EMAIL PROTECTED]> wrote:
>>>>>>>>>>
>>>>>>>>>>> IMHO,I think the statement about NN with regard to block
>>>>>>>>>>> metadata is more like a general statement. Even if you put lots of small
>>>>>>>>>>> files of combined size 10 TB , you need to have a capable NN.
>>>>>>>>>>>
>>>>>>>>>>> can disct cp be used to copy local - to - hdfs ?
>>>>>>>>>>>
>>>>>>>>>>> Thanks,
>>>>>>>>>>> Rahul
>>>>>>>>>>>
>>>>>>>>>>>
NEW: Monitor These Apps!
elasticsearch, apache solr, apache hbase, hadoop, redis, casssandra, amazon cloudwatch, mysql, memcached, apache kafka, apache zookeeper, apache storm, ubuntu, centOS, red hat, debian, puppet labs, java, senseiDB