The In-Out Column 其代表执行步骤的 串行与并行输入输出情况
SERIAL (blank): Serial execution. Currently, SQL is not loaded in the OTHER column for this case. SERIAL_FROM_REMOTE (S -> R): Serial execution at a remote site. PARALLEL_FROM_SERIAL (S -> P): Serial execution. Output of step is partitioned or broadcast to parallel execution servers. PARALLEL_TO_SERIAL (P -> S): Parallel execution. Output of step is returned to serial QC process. PARALLEL_TO_PARALLEL (P -> P): Parallel execution. Output of step is repartitioned to second set of parallel execution servers. PARALLEL_COMBINED_WITH_PARENT (PWP): Parallel execution; Output of step goes to next step in same parallel process. No interprocess communication to parent. PARALLEL_COMBINED_WITH_CHILD (PWC): Parallel execution. Input of step comes from prior step in same parallel process. No interprocess communication from child. https://docs.oracle.com/database/121/TGSQL/tgsql_interp.htm#TGSQL94734
