Josh, this morning I woke up and remembered that I wrote http://affy.blogspot.com/2012/11/how-can-i-use-reverse-sort-on-generic.html about 18 months ago. I can easily add a reverse index in order to extend the D4M schema.
I'm glad to see that reverse scanning is possible in HBase. On Thu, May 15, 2014 at 8:43 PM, Josh Elser <[email protected]> wrote: > Reverse scanning isn't necessarily infeasible: https://issues.apache.org/ > jira/browse/HBASE-4811 > > 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 >> (https://github.com/medined/D4M_Schema) web application, I started >> thinking about how to paginate. The results are at >> https://github.com/medined/D4M_Schema/blob/master/docs/pagination.md. >> 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. >> >>
