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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.
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
Q1,01
Q1,02
Q1,03
Q1,04
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.
