Materialize

Normally nodes return their output row when their parent node asks for them. Sometimes when executing a subselect or inside part of a join, the planner might consider it more efficient to materialize that node instead. This produces the entire row set at once instead of having each upper limit row grab them. This is rare enough that it's hard to even show a good example of it.

A much more common use of Materialize involves Merge Joins and in some cases Nested Loops, and those are specifically covered in a later section.