Show per-shard data size

[vladzcloudius]

System information

• Are you willing to contribute it: No

Describe the feature and the current behavior/state.
Show a histogram/graph of per-shard data size.
It makes sense to have it on a per-node level and be able to aggregate (show the average) on a per-DC and per-Cluster level.

Who will benefit with this feature?
This is useful when debugging performance issues.

[amnonh]

@vladzcloudius what do you mean by data size?

[vladzcloudius]

@vladzcloudius what do you mean by data size?

Amount of data on disk, @amnonh.

[amnonh]

Is that different than #1590

[vladzcloudius]

Is that different than #1590

Not exactly. nodetool status doesn't show per-shard data size.