stack-3 wrote:
>
> On Wed, Sep 9, 2009 at 7:52 PM, Keith Thomas <[email protected]>
> wrote:
>
>>
>> I think I'm looking at the same problem with HBase as Dingding Ye. I need
>> to
>> be able to retrieve a list of rows sorted by data in a column and I'm not
>> sure how to go about it without resorting to performing the sort on the
>> client which feels like I'm just giving up.
>>
>>
>
> s3> You want to sort rows in the table by other than the row key or is it
> just
> s3> that you want to sort the content of a row by other than its column
> name?
>
> I want to sort by the content of a column in each row.
>
> s3> How big is the set you want to look at? Is it full table or some
> subset of
> rows?
>
> I am writing the data access layer, not the app itself. I have to conform
> to a certain api. It is up to the application itself to use certain
> limits, although I may impose configurable limits in my layer just to be
> conservative in this brave new world I am exploring. Idelly I'd like to be
> able to to both, i.e. retrieve a full table or a subset. I think that once
> I've written the full table support I's worry about collecting just a
> subset.
>
>
>> My current thinking is to create a map class that outputs key/value pairs
>> where the key is the field I want to sort upon and the value is row key.
>> This way I will get nice sorted input going into my reduce class. I guess
>> I
>> would have to have once reduce class instance.
>>
>
> s3> Why one reduce? Write your own partitioner and impose a total order?
> Thanks, I will read up on this, thanks for the direction.
>
>
>
>>
>> However, I am unclear how I can return the row keys and the families with
>> their column data to the client from the reduce class. All the examples I
>> have found so far write the results to files/tables whereas I want to
>> return
>> objects to a client.
>>
>
> s3>Yeah.... bit tough making your client into a reduce sink (Can be done,
> it
> s3>just has to be available to the full cluster)
>
> I guess the thing I'm definitely completely stuck upon is how to get
> something like Result back to the client when I' writing my own map/reduce
> classes.
>
>>
>> In the Hadoop Javadocs I notice a bunch of Comparators but as yet I've
>> not
>> figure out their purpose. If I spend the cycles understanding the purpose
>> of
>> these Comparators are they likely to be of help to me in formulating an
>> alternate/better approach to that described above?
>>
>
>
> s3> In HBase all is lexicographically ordered. Tables are ordered by
> rows. Row
> s3> content is ordered by columns.
>
> Thanks
>
> St.Ack
>
>
>>
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>>
>>
>
>
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