Metrics logging

[Dan Sarisky]

We are seeing a steady stream of writes into reaper_db.node_metrics_v3 on our clusters when running in sidecar mode.

When I look at nodetool tpstats, I see the below output.  Which says that for the 27.6 million writes we've done over time, we have done ZERO reads.  I see looking in the code that there are various rest api calls to access this information, but it sure doesn't look like the normal path of operation of reaper needs this data.  It looks to me like we are capturing this data regularly (and a fair bit of it) but nothing is reading it.  Do I have tihs wrong?

Table: node_metrics_v3

SSTable count: 3

Space used (live): 779169

Space used (total): 779169

Space used by snapshots (total): 0

Off heap memory used (total): 1039337

SSTable Compression Ratio: 0.25907884740160714

Number of partitions (estimate): 82

Memtable cell count: 11888

Memtable data size: 667422

Memtable off heap memory used: 1038537

Memtable switch count: 251

Local read count: 0

Local read latency: NaN ms

Local write count: 27624486

Local write latency: 0.060 ms

Pending flushes: 0

Percent repaired: 0.0

Bloom filter false positives: 0

Bloom filter false ratio: 0.00000

Bloom filter space used: 144

Bloom filter off heap memory used: 120

Index summary off heap memory used: 312

Compression metadata off heap memory used: 368

Compacted partition minimum bytes: 8240

Compacted partition maximum bytes: 73457

Compacted partition mean bytes: 37706

Average live cells per slice (last five minutes): NaN

Maximum live cells per slice (last five minutes): 0

Average tombstones per slice (last five minutes): NaN

Maximum tombstones per slice (last five minutes): 0

Dropped Mutations: 0