I found this issue after debugging a performance problem on an OpenTSDB cluster, it was basically unusable after an upgrade from 0.94.2 to 0.94.6. It was caused by
HBASE-7279 (ping [~lhofhansl]).
The easiest way to see it is to run a simple 1 client PE:
Then in the shell do a filter scan (flush the table first and make sure if fits in your blockcache if you want stable numbers).
I tried a bunch of 0.94, up to 0.94.11, and the tip of 0.96. They are all slow like this.
It seems that since that jira went in we do a lot more row matching, and running the regex gets super expensive.