cost time of 0.7 tinkerpop test

clear schema

backend	structure test	process test
memory	4m28s	2m2s
rocksdb	9h41m	>2h
cassandra	10m12s	8m03s
hbase	20m	17m
mysql	24m	25m17s

truncate table

backend	structure test	process test
memory	41s	21s
rocksdb	3m40s	2m10s
cassandra	18m31s	18m43s
hbase	>5h	1h44m
mysql	14m56s	16m30s