I have a few use cases where I'd like to leverage HBase's high write throughput to blindly write lots of data even if most of it hasn't changed since the last write. I want to retain MAX_VERSIONS=Integer.MAX_VALUE, however, I don't want to keep all the duplicate copies around forever. At compaction time, I'd like the compactor to compare the values of cells with the same row/family/qualifier and only keep the *oldest* version of duplicates. By keeping the oldest versions I can get a snapshot of a row at any historical time.
Lars, I think you said Salesforce retains many versions of cells - do you retain all the duplicates? I'm guessing co-processors would be the solution and am looking for some pointers on the cleanest way to implement it or some code if anyone has already solved the problem. I'm also wondering if people think it's a generic enough use case that HBase could support it natively, say, with a column family attribute DISCARD_NEWEST_DUPLICATE=true/false. The cost would be higher CPU usage at compaction time because of all the value comparisons. Thanks for any tips, Matt
