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From Nithin Asokan <anithi...@gmail.com>
Subject Re: Question about HBaseSourceTarget
Date Wed, 18 Mar 2015 01:13:23 GMT
Thanks for looking at this everyone.

I can try the suggestion Gabriel posted here, I'm not familiar with the
HBaseFrom.table(String) API, and tried searching online. It will be really
helpful if someone can point me to the API.

Thanks everyone!

On Tue, Mar 17, 2015 at 3:34 PM Gabriel Reid <gabriel.reid@gmail.com> wrote:

> Yep, that looks like it could be pretty handy -- according to that ticket
> it's in 0.98.1 as well.
>
>
> On Tue, Mar 17, 2015 at 8:54 PM Josh Wills <jwills@cloudera.com> wrote:
>
>> Would this help for 0.99+?
>>
>> https://issues.apache.org/jira/browse/HBASE-10413
>>
>> On Tue, Mar 17, 2015 at 12:35 PM, Gabriel Reid <gabriel.reid@gmail.com>
>> wrote:
>>
>>> That sounds like it would work pretty well, although the situation where
>>> a custom Scan is used is still problematic.
>>>
>>> I think Hannibal [1] does some clever stuff as far as figuring out data
>>> size as well (I think just via HBase RPC and not by looking at HDFS), there
>>> could be some useful ideas in there.
>>>
>>> - Gabriel
>>>
>>> 1. https://github.com/sentric/hannibal
>>>
>>>
>>> On Tue, Mar 17, 2015 at 5:27 PM Micah Whitacre <mkwhitacre@gmail.com>
>>> wrote:
>>>
>>>> Could we make an estimate based on # of regions * hbase.hregion.max.filesize?
>>>>  The case where this would overestimate would be if someone pre-split
>>>> a table upon creation.   Otherwise as the table fills up over time in
>>>> theory each region would grow and split evenly (and possibly hit max size
>>>> and therefore split again).
>>>>
>>>> On Tue, Mar 17, 2015 at 11:20 AM, Josh Wills <jwills@cloudera.com>
>>>> wrote:
>>>>
>>>>> Also open to suggestion here-- this has annoyed me for some time (as
>>>>> Gabriel pointed out), but I don't have a good fix for it.
>>>>>
>>>>> On Tue, Mar 17, 2015 at 9:10 AM, Gabriel Reid <gabriel.reid@gmail.com>
>>>>> wrote:
>>>>>
>>>>>> Hi Nithin,
>>>>>>
>>>>>> This is a long-standing issue in Crunch (I think it's been present
>>>>>> since Crunch was originally open-sourced). I'd love to get this fixed
>>>>>> somehow, although it seems to not be trivial to do -- it can be difficult
>>>>>> to accurately estimate the size of data that will come from an HBase
table,
>>>>>> especially considering that filters and selections of a subset of
columns
>>>>>> can be done on an HBase table.
>>>>>>
>>>>>> One short-term way of working around this is to add a simple identity
>>>>>> function directly after the HBaseSourceTarget that implements the
>>>>>> scaleFactor method to manipulate the calculated size of the HBase
data, but
>>>>>> this is just another hack.
>>>>>>
>>>>>> Maybe the better solution would be to estimate the size of the HBase
>>>>>> table based on its size on HDFS when using the HBaseFrom.table(String)
>>>>>> method, and then also overload the HBaseFrom.table(String, Scan)
method to
>>>>>> also take a long value which is the estimated byte size (or perhaps
scale
>>>>>> factor) of the table content that is expected to be returned from
the given
>>>>>> Scan.
>>>>>>
>>>>>> Any thoughts on either of these?
>>>>>>
>>>>>> - Gabriel
>>>>>>
>>>>>>
>>>>>> On Tue, Mar 17, 2015 at 1:51 PM Nithin Asokan <anithin19@gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>> Hello,
>>>>>>> I came across a unique behavior while using HBaseSourceTarget.
>>>>>>> Suppose I
>>>>>>> have a job(from MRPipeline) that reads from HBase using
>>>>>>> HBaseSourceTarget
>>>>>>> and passes all the data to a reduce phase, the number of reducers
>>>>>>> set by
>>>>>>> planner will be equal to 1. The reason being [1]. So, it looks
like
>>>>>>> the
>>>>>>> planner assumes there is only about 1Gb of data that's read from
the
>>>>>>> source, and sets the number of reducers accordingly. However,
let's
>>>>>>> say my
>>>>>>> HBase scan is returning very less data or huge amounts of data.
The
>>>>>>> planner
>>>>>>> still assigns 1 reducer(crunch.bytes.per.reduce.task=1Gb). What
more
>>>>>>> interesting is, if there are dependent jobs, the planner will
set the
>>>>>>> number of reducers based on the initially determined size from
HBase
>>>>>>> source.
>>>>>>>
>>>>>>> As a fix for the above problem, I can set the number of reducers
on
>>>>>>> the
>>>>>>> groupByKey(), but that does not offer much flexibility when dealing
>>>>>>> with
>>>>>>> data that is of varying sizes. The other option, is to have a
map
>>>>>>> only job
>>>>>>> that reads from HBase and writes to HDFS and have a run(). The
next
>>>>>>> job
>>>>>>> will determine the size right, since FileSourceImpl calculates
the
>>>>>>> size on
>>>>>>> disk.
>>>>>>>
>>>>>>> I noticed the comment on HBaseSourceTarget, and was wondering
if
>>>>>>> there was
>>>>>>> anything planned to have it implemented.
>>>>>>>
>>>>>>> [1]
>>>>>>>
>>>>>>> https://github.com/apache/crunch/blob/apache-crunch-0.8.4/crunch-hbase/src/main/java/org/apache/crunch/io/hbase/HBaseSourceTarget.java#L173
>>>>>>>
>>>>>>> Thanks
>>>>>>> Nithin
>>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Director of Data Science
>>>>> Cloudera <http://www.cloudera.com>
>>>>> Twitter: @josh_wills <http://twitter.com/josh_wills>
>>>>>
>>>>
>>>>
>>
>>
>> --
>> Director of Data Science
>> Cloudera <http://www.cloudera.com>
>> Twitter: @josh_wills <http://twitter.com/josh_wills>
>>
>

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