• the planned statement(s) (trees of Plan nodes)
• run-time versions of Plan nodes (under QueryDesc)
• description of result tuples (under TupleDesc)
• overall state of scan through result tuples (e.g. atStart)
• other context information (transaction, memory, ...)

PortalRun() function also requires

• destination for query results (e.g. connection to client)
• scan direction (forward or backward)