New filter type: a filter that can return results that it has fabricated (use
for doing sum, count, etc.)
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Key: HBASE-1512
URL: https://issues.apache.org/jira/browse/HBASE-1512
Project: Hadoop HBase
Issue Type: Improvement
Reporter: stack
Chatting with jgray and holstad at the kitchen table about counts, sums, and
other aggregating facility, facility generally where you want to calculate some
meta info on your table, it seems like it wouldn't be too hard making a filter
type that could run a function server-side and return the result ONLY of the
aggregation or whatever.
For example, say you just want to count rows, currently you scan, server
returns all data to client and count is done by client counting up row keys. A
bunch of time and resources have been wasted returning data that we're not
interested in. With this new filter type, the counting would be done
server-side and then it would make up a new result that was the count only
(kinda like mysql when you ask it to count, it returns a 'table' with a count
column whose value is count of rows). We could have it so the count was just
done per region and return that. Or we could maybe make a small change in
scanner too so that it aggregated the per-region counts.
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