tag:blogger.com,1999:blog-5124641802818980374.post8642259619441444828..comments2023-09-06T11:58:30.752+02:00Comments on Oracle related stuff: 12c Parallel Execution New Features: 1 SLAVE distributionUnknownnoreply@blogger.comBlogger3125tag:blogger.com,1999:blog-5124641802818980374.post-84978521075145695462023-03-20T18:53:34.706+01:002023-03-20T18:53:34.706+01:00Really sorry about that Randolf. I was reading cou...Really sorry about that Randolf. I was reading couple of blogs around that time - one from Christian Antognini and I probably messed up. Apologies. Thank you for answering the questions. Vishal Beriwalhttps://www.blogger.com/profile/14355927507462358558noreply@blogger.comtag:blogger.com,1999:blog-5124641802818980374.post-57602957562662804712020-05-14T17:25:01.770+02:002020-05-14T17:25:01.770+02:00Hi Vishal,
Randolf here - Christian might be Chri...Hi Vishal,<br /><br />Randolf here - Christian might be Christian Antognini? But that's not his blog :-)<br /><br />Anyway - if you read the blog carefully you'll notice that there are pros and cons having multiple DFO trees - one of the potential drawbacks of having everything in one DFO tree is that you can end up with more "BUFFERED" hash joins.<br /><br />What I'm trying to say here is that this isn't black and white and as so often depends on a lot of details which of the two variants might be more desirable and this can change from case to case.<br /><br />Having said that, to answer your questions:<br /><br />1. There is no direct way to control the number of DFO trees, no matter which version you run. The number of DFO trees depends on the SQL features used and the execution plan generated by the optimizer. You do have some indirect control by replacing one feature with another (for example don't use materialized WITH clauses, don't use certain kind of Analytic Functions, don't make use of ROWNUM etc.)<br /><br />2. The 1 SLAVE feature described here isn't backported to pre-12c as far as I know. You need at least a 12c optimizer code to get support for that feature (which means using for example OPTIMIZER_FEATURES_ENABLE = 11.2.0.4 in 12c and later will prevent the feature).<br /><br />RandolfRandolfhttps://www.blogger.com/profile/13463198440639982695noreply@blogger.comtag:blogger.com,1999:blog-5124641802818980374.post-86539970513899571762020-05-13T20:28:47.641+02:002020-05-13T20:28:47.641+02:00Hi Christian
Couple of questions here.
1. As you...Hi Christian<br /><br />Couple of questions here.<br /><br />1. As you said, multiple DFO trees could be undesirable. Is there a way we can control the number of DFO trees on 11.2.0.4 ?<br /><br />2. And about this 1SLAVE new feature which addresses the multiple DFO problem. Is there a fix for this that could be backported to 11.2.0.4 ?<br />Vishal Beriwalhttps://www.blogger.com/profile/14355927507462358558noreply@blogger.com