It's in-memory materialization, which will spill to disk if it doesn't fit in memory. Search for "Materialize node" in https://www.postgresql.org/docs/12/using

It's in-memory materialization, which will spill to disk if it doesn't fit in memory. Search for "Materialize node" in https://www.postgresql.org/docs/12/using-explain.html https://www.postgresql.org/docs/12/using-explain.html