Optimize row_key_index to avoid causing Cassandra large partitions

[mohabusama]

The current implementation could cause large partitions in Cassandra.
Possible solutions:

SOLUTION I
Remove dependency on row_key_index

• Can KairosDB work without a row_key_index?

SOLUTION II
time-bucket row_key_index

• Rotate row_key_index with data_points

[alexkorotkikh]

As an option:

SOLUTION III:
Change the data model, to store metric names as metric names instead of tags, like now.

Currently:
zmon.check.2018--my_instance-cpu_avg

Should be:
zmon.check.2018.cpu_avg--my_instance

Then row_key_index would be partitioned not by check_id (zmon.check.2018) but by actual metric name (zmon.check.2018.cpu_avg in this case), and partition sizes may be decreased drastically.