In a query's lifecycle, at attempt is made to initialize each enabled storage plugin, while building the schema tree. This is done regardless of the actual plugins involved within a query.
Sometimes, when one or more of the enabled storage plugins have issues - either due to misconfiguration or the underlying datasource being slow or being down, the overall query time taken increases drastically. Most likely due the attempt being made to register schemas from a faulty plugin.
For example, when a jdbc plugin is configured with SQL Server, and at one point the underlying SQL Server db goes down, any Drill query starting to execute at that point and beyond begin to slow down drastically.
We must skip registering unrelated schemas (& workspaces) for a query.