Add Exporter as an Option for Locust Stats

[andrewbaldwin44]

Proposal

1. Add a new module LocustExporter, which will export stats to a given InfluxDB instance
2. Add a new flag --exporter, which will export the stats when active
3. Add documentation to explain the usage

[cyberw]

I'm less versed then you are in InfluxDB, but shouldnt it be just one measurement (request)? Wouldnt that make queries etc much easier?

[andrewbaldwin44]

It helps us to separate the failed requests versus the successful ones, for example, if we wanted to know the number of errors, we could use a query like so:

from(bucket: v.bucket)
  |> range(start: v.timeRangeStart, stop: v.timeRangeStop)
  |> filter(fn: (r) => r["_field"] == "response_time" and r["_measurement"] == "request_failure")
  |> count()

[cyberw]

Yes, but what about the (slightly more common) queries where we want all requests? At least that is how I would do it in SQL...

[andrewbaldwin44]

from(bucket: v.bucket)
  |> range(start: v.timeRangeStart, stop: v.timeRangeStop)
  |> filter(fn: (r) => r["_field"] == "response_time")

Would give back all requests
But yeah on the other hand, then we could also count errors like

from(bucket: v.bucket)
  |> range(start: v.timeRangeStart, stop: v.timeRangeStop)
  |> filter(fn: (r) => r["_field"] == "exception")

So I think it's just a matter of preference

[cyberw]

Just reading the docs (https://docs.influxdata.com/influxdb/cloud/write-data/best-practices/schema-design/) I think we should store a tag success (with true/false value), for logically consistent storage (failed and successful requests are not fundamentally different things) and equally fast querying. But lets chat about it on monday.

[andrewbaldwin44]

Yeah so based on the docs it definitely makes sense to just have the one measurement. Whether or not we want to have the tag success, we should decide if it's useful. Like I mentioned, since we could query for failures with r["_field"] == "exception", we don't necessarily need a success field

[cyberw]

Don't we need it to be a tag for faster querying? Fields arent indexed, right?

[andrewbaldwin44]

Yup sorry! For some reason I was thinking exception was a tag but obviously it's not