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Sqoop, mail # user - Strange distribution of keys among mappers


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David Kincaid 2013-06-19, 15:33
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Abraham Elmahrek 2013-06-19, 20:14
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David Kincaid 2013-06-19, 20:23
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Abraham Elmahrek 2013-06-19, 22:48
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David Kincaid 2013-06-19, 23:05
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Re: Strange distribution of keys among mappers
Abraham Elmahrek 2013-06-19, 23:21
Hey David,

With oracle, the BigDecimalSplitter will be used by default for all number
types.

-Abe
On Wed, Jun 19, 2013 at 4:05 PM, David Kincaid <[EMAIL PROTECTED]>wrote:

> Abe, the database is Oracle.
>
>
> On Wed, Jun 19, 2013 at 5:48 PM, Abraham Elmahrek <[EMAIL PROTECTED]>wrote:
>
>> David,
>>
>> What database are you importing from? The description I gave was for
>> datatypes that map to the BigDecimal Splitter. The userguide might be
>> referring to the IntegerSplitter which will add the remainder to the last
>> value.
>>
>> -Abe
>>
>>
>> On Wed, Jun 19, 2013 at 1:23 PM, David Kincaid <[EMAIL PROTECTED]>wrote:
>>
>>> Thanks. We didn't specify the number of mappers, so it's giving us 4. I
>>> understand your explanation, but it seems to conflict with the Sqoop user
>>> guide (
>>> http://sqoop.apache.org/docs/1.4.3/SqoopUserGuide.html#_controlling_parallelism
>>> ):
>>>
>>> "When performing parallel imports, Sqoop needs a criterion by which it
>>> can split the workload. Sqoop uses a *splitting column* to split the
>>> workload. By default, Sqoop will identify the primary key column (if
>>> present) in a table and use it as the splitting column. The low and high
>>> values for the splitting column are retrieved from the database, and the
>>> map tasks operate on evenly-sized components of the total range. For
>>> example, if you had a table with a primary key column of id whose
>>> minimum value was 0 and maximum value was 1000, and Sqoop was directed to
>>> use 4 tasks, Sqoop would run four processes which each execute SQL
>>> statements of the form SELECT * FROM sometable WHERE id >= lo AND id <
>>> hi, with (lo, hi) set to (0, 250), (250, 500), (500, 750), and (750,
>>> 1001) in the different tasks."
>>>
>>>
>>> On Wed, Jun 19, 2013 at 3:14 PM, Abraham Elmahrek <[EMAIL PROTECTED]>wrote:
>>>
>>>> Hey David,
>>>>
>>>> Here's the algorithm:
>>>> Split lengths are defined by (max - min)/(# mappers) and whatever is
>>>> left is tacked on at the end. So in this case, (288272191-2110)/3 >>>> 96090027.33... So I'm assuming the .33... is rounded down and split lengths
>>>> will be of length 96090027. Sqoop will then create splits with the
>>>> following points: (min) + (range length)*(n). We can see that 2110 + 96090027*0
>>>> = 2110, 2110 + 96090027*1 = 96092137, 2110 + 96090027*2 = 192182164,
>>>> and 2110 + 96090027*3 = 288272191 will be generated based off of this
>>>> algorithm. The last point to be added will be 288272192 because the
>>>> max value is not part of the generated split points. Then sqoop will
>>>> distributed accordingly based off of these points as you've pointed out
>>>> above.
>>>>
>>>> Just to be sure, did you configure sqoop to use 3 mappers?
>>>>
>>>> Hope this helps,
>>>> -Abe
>>>>
>>>>
>>>> On Wed, Jun 19, 2013 at 8:33 AM, David Kincaid <[EMAIL PROTECTED]>wrote:
>>>>
>>>>> We're seeing a strange thing happen with a sqoop import job with the
>>>>> way the key range is getting distributed among the 4 mappers that are
>>>>> running. The minimum key value is 2110 and the maximum value is 288272191.
>>>>> We are getting one mapper that is only getting one record to import. Here
>>>>> is the distribution among the mappers:
>>>>>
>>>>> [2110, 96092137)
>>>>> [96092137, 192182164)
>>>>> [192182164, 288272191)
>>>>> [288272191, 288272192)
>>>>>
>>>>> you can see that the fourth mapper is given a range with only one
>>>>> value in it. Could someone help me understand what is going on?
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Dave
>>>>>
>>>>
>>>>
>>>
>>
>
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Abraham Elmahrek 2013-06-19, 23:31
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Abraham Elmahrek 2013-06-19, 23:50
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David Kincaid 2013-06-20, 00:03
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Abraham Elmahrek 2013-06-20, 00:30
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David Kincaid 2013-06-20, 00:33
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David Kincaid 2013-06-19, 23:25