RE: "direct path read" and "db file sequential read" used for full table scans in 11g

  • From: "Allen, Brandon" <Brandon.Allen@xxxxxxxxxxx>
  • To: "oracle-l@xxxxxxxxxxxxx" <oracle-l@xxxxxxxxxxxxx>
  • Date: Thu, 30 Aug 2012 21:47:29 +0000

Question #3 is open again
According to the docs the answer I thought I'd found would only explain what 
I'm seeing if I had the parameter parallel_degree_policy=AUTO, but I just 
checked and it is set to MANUAL, so the parallel queries should still be using 
direct path reads according to the doc: 
http://docs.oracle.com/cd/E11882_01/server.112/e25513/initparams179.htm#REFRN10310

SQL> show parameter PARALLEL_DEGREE_POLICY

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------
parallel_degree_policy               string      MANUAL


From: Allen, Brandon

I found the answer to question #3 - apparently it's a new feature called 
"In-Memory Parallel Execution" as documented at the links below.  I'm still 
looking for answers on #1 and 2 though if anyone has any ideas.


From: Allen, Brandon



1)      How can I force production to use the direct path reads?

2)      Why is it using "db file sequential read" for a full table scan instead 
of "db file scattered read"?

3)      I also tried setting PARALLEL to 2 on the table in question and it did 
force Oracle to use a parallel execution plan, but it still used "db file 
sequential read" instead of "direct path read" - any idea why this could be?


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