Wat is Out-of-core processing, streaming execution?

Out-of-core processing computes a result over data larger than memory by reading it in pieces from storage. Streaming execution is the engine-level form of it: the plan’s operators pass batches to one another as they are produced, so that a scan, a filter and an aggregation hold one batch at a time, while operators that need all of their input (a global sort, some joins) buffer it.