I am reading an article about Understanding Parallel Execution

There is a paragraph which is as follows:


But for my understanding of how to read an execution plan, this parallel execution plan starts from operation 7 not operation 14.

Why this article emphasize that the execution plan starts at operation 14?? It upside down my knowledge of execution plan.

1 Answer 1


According to the quoted text Oracle will only have two parallel active per data flow operation. Take a look at the TQ column of the EXPLAIN PLAN. There is only one data flow operation for this query (Q1). There are five different parallel slave sets for Q1:


Q1,00 and Q1,01 will be processed first. The operation on line 7 (FTS on T3) has a slave set of Q1,02 so it can only start after Q1,00 or Q1,01 finish and free up a slave set.

  • does parallel execution plan not execute by the execution tree order?
    – shawn
    Jan 5, 2017 at 3:43
  • As far as I can tell that is the point that the author is making: "Second, if you know how to interpret serial execution plans regarding the order of execution, you might be surprised by the fact that the Consumer / Producer model, along with the buffering, can lead to scenarios where the usual rules do not apply."
    – Joe Obbish
    Jan 5, 2017 at 5:34

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.