Warn users of full table scans before executing recipes

natejgardner

Explain plans indicate whether a full table scan will occur in most databases. Ideally, if a recipe is about to perform a full table scan, users could be warned before executing the first time, and a warning could be placed on a recipe itself, indicating it requires a full table scan to run. This will encourage users to optimize before running a potentially memory intensive or long-running query. If the row count of an input dataset is high, this becomes especially important to know ahead of time.