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Pig >> mail # user >> number of reducers


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Alex Rovner 2012-06-01, 15:49
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Bill Graham 2012-06-01, 16:55
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Alex Rovner 2012-06-01, 19:29
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Ashutosh Chauhan 2012-06-01, 18:02
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Alex Rovner 2012-06-01, 19:33
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Re: number of reducers
HCatalog does not require it's own metadata.  It shares the mysql database with Hive.  All of this is much cleaner and clearer now in the 0.4 release of HCatalog, since it is now a set of jars for use on the client side.  It depends on you setting up a Hive metastore first.

There is a Hive load function in Piggybank that you could look at, but hopefully with the new 0.4 release of HCatalog it will be light enough to accomplish what you need.

Alan.

On Jun 1, 2012, at 12:33 PM, Alex Rovner wrote:

> Ashutosh,
>
> The issues we had are probably not relevant anymore as we were using 2.0
> release with pig version 8 or 9.
>
> We can certainly attempt to use HCatalog again in the near future.
>
> Two general question I had about the design:
>
> Why does HCatalog need it's own MySQL database? Why cant it just leverage
> Hives metadata?
> Is it possible to create a loader / storage func that works off existing
> Hive metadata without the need to install Hcatalog. This could be useful to
> folks like us who don't need the full feature set of Hcatalog but would
> rather just want to read / write data to Hive with PIG.
>
> Thanks
> Alex
>
> On Fri, Jun 1, 2012 at 2:02 PM, Ashutosh Chauhan <[EMAIL PROTECTED]>wrote:
>
>>>> (HCatalogue had roadblocks at the time and we decided against using it)
>> Off-topic, but it would be great if you can let us know what were those
>> roadblocks. We will try to address those if those are still there.
>>
>> Thanks,
>> Ashutosh
>>
>> On Fri, Jun 1, 2012 at 8:49 AM, Alex Rovner <[EMAIL PROTECTED]> wrote:
>>
>>> Hello,
>>>
>>> We have wrote a HiveLoader that loads data from a hive warehouse
>>> (HCatalogue had roadblocks at the time and we decided against using it)
>>>
>>> We have one minor issue that would be great to solve: Currently pig
>> cannot
>>> estimate correctly how many reducers to use when loading data from a hive
>>> warehouse.
>>>
>>> We have looked through the code and traced the problem to the following:
>>>
>>> Pig is using the location returned from "relativeToAbsolutePath" to
>> figure
>>> out how many reducers it needs. In the case of loading from Hive, we do
>> not
>>> know the paths that we need to load up until the setPartition() call is
>>> made. We can of course set the root of the table as the path in the
>>> "relativeToAbsolutePath" call but that would make pig over-estimate the
>>> number of reducers needed since we wont take into account the partition
>>> filtering that is taking place.
>>>
>>> Are there any workarounds for this issue?
>>> From my understanding, it would be sufficient if the
>> relativeToAbsolutePath
>>> call was called after the setLocation and setPartition calls.
>>>
>>> Any input would be appreciated.
>>>
>>> Thanks
>>> Alex
>>>
>>