Prometheus read/write support

[iksaif]

See https://github.com/prometheus/prometheus/blob/HEAD/storage/remote/remote.proto for the protocol

[iksaif]

https://github.com/criteo/graphite-remote-adapter for the go part, which may have a biggraphite specific client.

First step: native Graphite implementation

Prefix all prometheus metrics by prometheus (or something configurable).
Always call /find first to get the list of metric, then call render. We call render once per metric (or maybe batch).
Only get data older than x amount of time (configurable)

• metric => prometheus.metric
• metric{label="value"} => prometheus.metric.** (check if we can stuf)
• `metric{environment=~"staging|testing|development",method!="GET"} (metrics.**)

We will probably want to heavilly cache the results.

Second step: BigGraphite implementation

On the write path:

• store the schema of the metric (how many labels, names of the labels). Put that in metrics_metadata.
• in the metrics table, store the value of the labels as components.
• cache the schema in carbon, if we receive a metric that doesn't match the current schema, discard it
• add a tool to change the schema (probably duplicating part of what bgutil copy does).

For the read path:

• =: easy
• !=, =~, !~: wildcard plus post-filtering. Might do some prefix matching in some cases.

First, use the Graphite read path and chose some special characters to do {label=value}. Later, have our own fast-path for prometheus.

[iksaif]

Work ongoing on https://github.com/criteo/graphite-remote-adapter