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Accumulo, mail # user - Record index within a Table


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michael_taylor@... 2012-12-04, 02:04
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Re: Record index within a Table
Josh Elser 2012-12-04, 02:30
Michael,

Accumulo doesn't expose any internal offsets of Key-Value pairs through
the API. While it might be able to extrapolate some of this knowledge
from the underlying structure of Accumulo, that isn't the intent of what
Accumulo is trying to provide.

The first idea that comes to mind is that you could write an
SortedKeyValueIterator which takes some array of indices you wish to
find in the ColQual ([3], in your case) and perform the heavy-lifting on
the server. Your SKVI can scan through the data, consuming records which
do not match your index ([3]). Since you know that Accumulo will not
split your row "1" across multiple server (a tablet is never split
across a row), you should be able to fairly quickly get a stream back of
all key for the relative indices you provided. You can think of this as
a sequential read over the disk which should be relatively efficient.

The only caveat is that you would need to create a range to scan over
your entire row+colfam, for example:

Range=(1 1: , 1 1\x00: )

Where the colqual is empty.

- Josh

On 12/3/2012 9:04 PM, [EMAIL PROTECTED] wrote:
> Does Accumulo have the idea of record index within a table?  As an
> example, take a table with the following values:
>
> Row  ColFam  ColQual
> 1        1            10
> 1        1            20
> 1        1            30
>
>
> As I understand it Accumulo will naturally sort the table in the above
> order (first by row, then by colFam, lastly by colQual).  If I insert
> (1, 1, 25), is there any way for me to get the index of the newly
> inserted value (3 in this case)?
>
> Further more is there anyway to lookup an index by knowing the full
> row:colFam:colQual key (say (1, 1, 30))?
>
> Lastly, is there an easy way to get the total number of rows within a
> table (and the same question for ColFam's within a row and ColQual's
> with a row:colFam pair)?
>
> I've made it through the documentation and scanned through the mailing
> list, but I haven't seen any information on the above (which lends me to
> believe I'm asking for behaviour that Accumulo doesn't natively provide).
>
> Many thanks for any information,
>
> - MT
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Josh Elser 2012-12-04, 17:45
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Christopher 2012-12-20, 18:31