When fetching from remote nodes, after obtaining initial group of rows, send down to the node that it should start producing the next batch so it is ready when we are ready to read them.
When fetching from remote nodes, after obtaining initial
group of rows, send down to the node that it should start producing
the next batch so it is ready when we are ready to read them.

Patch submitted by Jason

arcivanov/postgres-xl,arcivanov/postgres-xl,arcivanov/postgres-xl,arcivanov/postgres-xl,arcivanov/postgres-xl,arcivanov/postgres-xl