Flash Metrics Storage

bootstrap:

$ echo -e "max-index-length = 12288" > tidb.config

$ tiup playground nightly --db.config tidb.config

$ make 

$ ./bin/flash-metrics --config.file=./flashmetrics.yml.example 

Then, configure your grafana, add a new "prometheus" datasource with host 127.0.0.1:9977.