Hi, The (in)ability to do previous scans is baked in at a very low level. Allowing for a reverse-scan might add a significant amount of storage requirements (10-20% is non-trival on multi-TB data sets). Just like adding in the second link for a doubly linked list isn't cheap, neither would be reverse scanning.
-ryan On Sun, Mar 7, 2010 at 6:36 PM, Hua Su <huas...@gmail.com> wrote: > On Sun, Mar 7, 2010 at 11:20 PM, Michael Segel > <michael_se...@hotmail.com>wrote: > >> >> What you're attempting to recreate is a 'scroll cursor'. >> On very large data sets, this isn't trivial to do. >> >> I think if you look at the use cases, you'll think of some other way of >> achieving your specific goals. >> >> Just my opinion... >> > > Thank. I just do some experiments and the data set is not very large. > > >> >> -Mike >> >> >> > Date: Sat, 6 Mar 2010 19:38:19 -0800 >> > Subject: Re: Does the scanner interface have a "previous" method? >> > From: erikhols...@gmail.com >> > To: hbase-user@hadoop.apache.org >> > >> > Hey Hua! >> > I agree that this would be a nice to have feature for cases when you want >> to >> > fetch data in >> > ascending and descending order. You would need to store any extra indices >> > just open up >> > a different scanner. >> > The best way to do this now though is to store it in a different index. >> > >> > Good luck! >> > Erik >> >> _________________________________________________________________ >> Hotmail: Trusted email with Microsoft’s powerful SPAM protection. >> http://clk.atdmt.com/GBL/go/201469226/direct/01/ >> >
