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Hive, mail # user - Performance difference between tuning reducer num and partition table


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Re: Performance difference between tuning reducer num and partition table
Felix.徐 2013-07-01, 02:12
Hi Dean,

Thanks for your reply. If I don't set the number of reducers in the 1st run
, the number of reducers will be much smaller and the performance will be
worse. The total output file size is about 200MB, I see that many reduce
output files are empty, only 10 of them have data.

Another question is that , is there any documentation about the job
specific parameters of MapReduce and Hive?
2013/6/29 Dean Wampler <[EMAIL PROTECTED]>

> What happens if you don't set the number of reducers in the 1st run? How
> many reducers are executed. If it's a much smaller number, the extra
> overhead could matter. Another clue is the size of the files the first run
> produced, i.e., do you have 30 small (much less than a block size) files?
>
> On Sat, Jun 29, 2013 at 12:27 AM, Felix.徐 <[EMAIL PROTECTED]> wrote:
>
>> Hi Stephen,
>>
>> My query is actually more complex , hive will generate 2 mapreduces,
>> in the first solution , it runs 17 mappers / 30 reducers and 10 mappers /
>> 30 reducers (reducer num is set manually)
>> in the second solution , it runs 6 mappers / 1 reducer and 4 mappers / 1
>> reducers for each partition
>>
>> I do not know whether they could achieve the same performance if the
>> reducers num is set properly.
>>
>>
>> 2013/6/29 Stephen Sprague <[EMAIL PROTECTED]>
>>
>>> great question.  your parallelization seems to trump hadoop's.    I
>>> guess i'd ask what are the _total_ number of Mappers and Reducers that run
>>> on your cluster for these two scenarios?   I'd be curious if there are the
>>> same.
>>>
>>>
>>>
>>>
>>> On Fri, Jun 28, 2013 at 8:40 AM, Felix.徐 <[EMAIL PROTECTED]> wrote:
>>>
>>>> Hi all,
>>>>
>>>> Here is the scenario, suppose I have 2 tables A and B, I would like to
>>>> perform a simple join on them,
>>>>
>>>> We can do it like this:
>>>>
>>>> INSERT OVERWRITE TABLE C
>>>> SELECT .... FROM A JOIN B on A.id=B.id
>>>>
>>>> In order to speed up this query since table A and B have lots of data,
>>>> another approach is :
>>>>
>>>> Say I partition table A and B into 10 partitions respectively, and
>>>> write the query like this
>>>>
>>>> INSERT OVERWRITE TABLE C PARTITION(pid=1)
>>>> SELECT .... FROM A JOIN B on A.id=B.id WHERE A.pid=1 AND B.pid=1
>>>>
>>>> then I run this query 10 times concurrently (pid ranges from 1 to 10)
>>>>
>>>> And my question is that , in my observation of some more complex
>>>> queries, the second solution is about 15% faster than the first solution,
>>>> is it simply because the setting of reducer num is not optimal?
>>>> If the resource is not a limit and it is possible to set the proper
>>>> reducer nums in the first solution , can they achieve the same performance?
>>>> Is there any other fact that can cause performance difference between
>>>> them(non-partition VS partition+concurrent) besides the job parameter
>>>> issues?
>>>>
>>>> Thanks!
>>>>
>>>
>>>
>>
>
>
> --
> Dean Wampler, Ph.D.
> @deanwampler
> http://polyglotprogramming.com