I read this was possible but how?

[Geoffry Roberts <th...@gmail.com>]

I need to update a value, a numeric value, in Accumulo where the result is
the sum of the old and the new as opposed to the new simply replacing the
old.

I read in a white paper that it is possible but it didn't say how.  I
Googled and found a bit about Accumulo keeping a history that could be
summed.  Yes, I knew about the history so I suppose that might work.  But
it apparently requires compaction.  Really! At first blush, this doesn't
sound like such a solid solution.

My question is, Is this summing-of-the-history the way to achieve my
desired result or is there a better way?  Either way, how do you do that?

Thanks
-- 
There are ways and there are ways,

Geoffry Roberts

Re: I read this was possible but how?

[Billie Rinaldi <bi...@gmail.com>]

See the "Combiners" section of the user manual:
http://accumulo.apache.org/1.6/accumulo_user_manual.html#_combiners

It does not require a compaction if the combiner is configured on all
scopes; the summing will happen on the fly at scan time until it is
persisted in a compaction.  You can read more about scopes earlier in the
same section of the manual:
http://accumulo.apache.org/1.6/accumulo_user_manual.html#_iterators


On Tue, May 13, 2014 at 7:02 AM, Geoffry Roberts <th...@gmail.com>wrote:

> I need to update a value, a numeric value, in Accumulo where the result is
> the sum of the old and the new as opposed to the new simply replacing the
> old.
>
> I read in a white paper that it is possible but it didn't say how.  I
> Googled and found a bit about Accumulo keeping a history that could be
> summed.  Yes, I knew about the history so I suppose that might work.  But
> it apparently requires compaction.  Really! At first blush, this doesn't
> sound like such a solid solution.
>
> My question is, Is this summing-of-the-history the way to achieve my
> desired result or is there a better way?  Either way, how do you do that?
>
> Thanks
> --
> There are ways and there are ways,
>
> Geoffry Roberts
>