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From Eric Newton <eric.new...@gmail.com>
Subject Re: Combiner design clarification
Date Wed, 15 Jul 2015 12:53:46 GMT
This paragraph probably refers to the fact that Key/Values may be combined
using a sub-set of the files for a tablet.

If you have 5 files, and 3 of them are being merged in a compaction, you
won't see the keys from the other two files.  When you are doing a scan,
you will see all the entries.

-Eric




On Wed, Jul 15, 2015 at 5:15 AM, michael.griffiths3@baesystems.com <
michael.griffiths3@baesystems.com> wrote:

>  Hi all,
>
>
>
> I’m implementing a range of combiners and my assumption is that at scan
> time we will only have one single combined value returned (regardless of
> whether the versioning iterator is applied), however the documentation in
> the iterator_design.txt document isn’t clear whether that assumption is
> correct:
>
>
>
>
>
> *A second consideration is that a Combiner is not guaranteed to see every
> Key-Value pair*
>
> *which differ only by timestamp every time it is invoked. For example, if
> there are 5 Key-Value*
>
> *pairs in a table which only differ by the timestamps 1, 2, 3, 4, and 5,
> it is not guaranteed that*
>
> *every invocation of the Combiner will see 5 timestamps. One invocation
> might see the Values for*
>
> *Keys with timestamp 1 and 4, while another invocation might see the
> Values for Keys with the*
>
>
>
> *timestamps 1, 2, 4 and 5.*
>
>
>
>
>
> Is the above an implementation detail that we need to consider when
> writing combiners, but not for the client implementation? Will the client
> only have one value returned to it?
>
> Equally does the same statement above stay true for other forms of
> iterators that are not combiners?
>
>
>
> Many thanks,
>
>
>
> Michael
>
>
>
>
>
>
> *Michael Griffiths Developer BAE Systems Applied Intelligence *
> *___________________________________________________________ *
>  *E: *michael.griffiths3@baesystems.com
>
> BAE Systems Applied Intelligence, Surrey Research Park, Guildford, Surrey,
> GU2 7RQ.
> www.baesystems.com/ai
>
>
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