Could not resolve type id 'variance' into a subtype of [simple type, class io.druid.query.aggreg

I want to load druid-stats extension to use a standard deviation aggregator. I have added druid-stats to druid.extensions.loadList in common.runtime.properties inside both conf and conf-quickstart directories (and restarted my druid services) and I know that my query should include a variance aggregator. Directions at http://druid.io/docs/latest/development/extensions-core/stats.html also mentions that to use this feature, a variance aggregator must be included at indexing time.

{
“type” : “variance”,
“name” : “variance”,
“fieldName” : “variance”,
“inputType” : “variance”,
“estimator” : “latencyMs”
}

I added the above block of code to metricsSpec in Tranquility’s server.json file and when I run:

bin/tranquility server -configFile /home/minoobeyzavi/druid-0.10.0/conf-quickstart/tranquility/server.json

It says:

Could not resolve type id ‘variance’ into a subtype of [simple type, class io.druid.query.aggregation.AggregatorFactory]

How do I proceed?

And what does it mean by “estimator” ?

The metric in the server.json is the right spot, although Tranquility needs to be aware of the extension too. Check out “Loading Druid extensions” on https://github.com/druid-io/tranquility/blob/master/docs/configuration.md.

The “estimator” is described a little bit down in the docs you linked, it switches between different variance algorithms.