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From Josh Elser <>
Subject Re: Pagination in Accumulo (also D4M Data Explorer!)
Date Fri, 16 May 2014 00:43:35 GMT
Reverse scanning isn't necessarily infeasible:

This might be something cool that could be implemented to make this sort 
of thing easiser.

The pagination isolation you mention in Approach B is interesting. I'm 
curious as to how clone'ing tables would work to get you this. I imagine 
for a highly active system (read and write) this would start to break 
down pretty quickly.

I think having a "loose" interpretation of the actual page you're on 
would be easiest to implement without omitting data (your "next?"). This 
would be a bit easier with a reverse scanner. The "page" then becomes a 
bit of a guess -- really, it's just a guess at the section of records 
being viewed (e.g. 20% behind and 80% forward). That might make for a 
more honest pagination view instead of explicitly listing page numbers 
which you know will change.

Have you considered creating a reverse row index to get around the lack 
of a reverse scanner?

On 5/14/14, 3:19 PM, David Medinets wrote:
> While working on the D4M Data Explorer
> ( web application, I started
> thinking about how to paginate. The results are at
> I'll reproduce only the first paragraph below since I don't want you to
> miss out on my cool images.
> - First Paragraph -
> Pagination in Accumulo is not simple. Pages are not deterministic since
> the data can be constantly changing. Also authorization levels can
> change the number of returned results. Another consideration is that
> Accumulo tables can only be scanned forwards and not backwards. With
> these factors in mind, I am implementing the following technique. I hope
> the community can point out flaws and provide improvements.
> ---
> Several people helped to review the page via private emails. Thanks! If
> you want credit, please step-up and self-identify.
> p.s. - The D4M Data Explorer is not too existing just yet. But it should
> get better. If you're interested I'd be glad for any help.

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