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From Christopher <ctubb...@apache.org>
Subject Re: Scan-time iterators returning out-of-order rows
Date Thu, 02 Apr 2015 04:11:47 GMT
You should definitely not rely on this behavior. It goes against best
practices and is prone to error. It is not recommended.

On Wed, Apr 1, 2015, 20:03 Russ Weeks <rweeks@newbrightidea.com> wrote:

> A wonderful property of scan-time iterators is that they can emit row IDs
> in arbitrary order. Before I go off and build an index that relies on this
> behaviour, I'd like to get a sense of how likely it is to exist in future
> versions of Accumulo.
>
> I'd like to build an index like this (hopefully the ascii comes through, if
> not check here <https://gist.github.com/anonymous/1a64114da4b68a2ec822>):
>
>
>  row   | cf  | cq                | val
> -------------------------------------------------
>  p0    | i   | (prop_a, 7, r15)  | 1
>  p0    | i   | (prop_a, 8, r8)   | 1
>  p0    | i   | (prop_a, 9, r19)  | 1
> [...snip...]
>  p0    | d   | (r8, prop_a)      | 8
>  p0    | d   | (r8, prop_b)      | hello, world
>  p0    | d   | (r15, prop_a)     | 7
>  p0    | d   | (r15, prop_b)     | just testing
>  p0    | d   | (r19, prop_a)     | 9
>  p0    | d   | (r19, prop_b)     | something else
>
> Which is a pretty conventional partitioned index. I'd like to be able to
> issue a query like, "Tell me about prop_b for all documents where prop_a <
> 9" but I'm pretty sure that the only way this could work at scale is if
> it's OK for the iterator to return (p0, r15, prop_b, "just testing")
> followed by (p0, r8, prop_b, "hello, world").
>
> This works today - if you folks see any flaws in my reasoning please let me
> know - my question is, do you see this as functionality that should be
> preserved in the future?
>
> Thanks,
> -Russ
>

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