A couple of notes and general observations. Note all instances remained up for the entire duration of testing including burn in (all tests ran on the same hardware), and HDFS volumes were built on locally attached storage (hence C3 generation instances), so I controlled as much as possible for system level variance.
Results are quite similar among the releasing 1.x versions and 1.5-SNAPSHOT. Note measurements are reported in microseconds. I thought 1.5-SNAPSHOT might show performance regressions, but the surprise is in the other direction. It seems to be better performing in the YCSB scenarios than the other versions tested in most cases. There are general small trends toward improvement as reduction in latencies with the exception of workloads B and F. Workloads B and F, especially when run against 1.5-SNAPSHOT, may show reduced performance on inserts/mutations in trade for improved performance in reads/scanning. More testing needed.
