What is the InMemory data source?
Inmemory datasource allows you to fetch information from more than one datasource at the same time. You can then define joins and use these multiple datasource to create report.
Please give a sample or tutorial about this feature.
As of now we do not support ability to multiple data sources at the same. It is in the roadmap.
However if you would still want to use multiple datasources at the same time one work around is usage of data processing engines like Presto. Presto can connect to your multiple datasources, and Helical Insight can in turn connect to Presto. That way it is possible to connect to multiple data sources also.