Hbase offers co-processors which should be able to do this. And median *can* be accumulated in a small amount of memory. It is a little trickier than mean, but still doable.
On Tue, Sep 6, 2011 at 11:21 AM, Duane Moore <duane.mo...@issinc.com> wrote: > - Aggregation > Accumulo offers the ability to specify an aggregator for an individual > column family or column. This allows you to keep a row count, or summation > of numerical values that may be stored in a particular column. It would > appear the function has to operate on the subset of values stored for that > column in the table at a particular time since it keeps the aggregate > value in memory. So this may not be able to handle certain aggregation > functions like 'median' for instance. But functions like sum, max, min, > mean, and count should all be supportable. > I could not find a comparable feature within HBase, but HBase does offer > an atomic function called incremementColumnValue on the HTable class which > appears can be leveraged to provide aggregation behavior. >
