Oracle consultant Steve Adams notes that the collection iterator with a pickler several reported memory leak issues with pickler fetches, even in Oracle 11g. Oracle can't tell the difference between an empty collection and a 2 (0)| 01 | | 3 | COLLECTION ITERATOR PICKLER FETCH| | COLLECTION ITERATOR PICKLER FETCH Oracle Cardinality feedback was introduced in Oracle Database 11g Release 2. 1 | COLLECTION ITERATOR PICKLER FETCH| GET_TAB_PTF | 1 | | Hi Tom, Assume the below case: Type t1 is record (full_name varchar2(20), purchase_order number(10), purchase_date date, shipped_date.
Pickler Fetch – What is it? | Martin Widlake's Yet Another Oracle Blog
The latest release of the Oracle Database is here. On Unlearning and Modeling. Check out the new features here. Question and Answer. Whilst you are here, check out some content from the AskTom team: Latest Followup. You Asked Hi Tom, Assume the below case: And in the explain plan I am seeing 'pickler fetch' which is fine. My question here is: Like in this scenario I want the date column to be indexed collection iterator pickler fetch oracle 11g memory, so that we can perform 'Index Range Scan'?
The reason I am asking is, when I ran the explain plan, my Estimated rows and Actual rows are way off for this and this is resulting in query taking more time to execute. I am considering a global temporary table, but I am yet to test this approach.
There is not a native way to do this. If you did go down this path, you could then also use some of the facilities described by Adrian Billington to set cardinality dynamically. See http: I'm a fan of global temporary tables, but you might have similar issues - ie, first execution puts say 10 rows into the GTT, and later executions put say 10, rows into it.
Unless you hard parse each time, you query may be optimized for Hope this helps. Write a Review. Ravi from BA, India. Thanks for the tip, I have dropped the idea of GTT: I tried dynamic sampling but surprisingly it did not help: Am having serious doubts about this technique but it's worth a try I guess. November 16, - 4: Collection iterator pickler fetch oracle 11g from BA India. I am an idiot, I was typing the syntax for dynamic sampling wrongly all the time!!!
Indexing GTT is something am also thinking, will update you once I get any solid results thanks a lot for your help: More to Explore. Dev Gym Classes, workouts and quizzes on Oracle Database technologies. Expertise through exercise!
Adaptive Query Optimization in Oracle Database 12c is made up of a number of different features. Functionality like Adaptive Plans allow modification of the execution plan at runtime, but these modifications do not allow the join order of the plan to change. Automatic Reoptimization is based on learning lessons from a previous execution and feeding that information back to the optimizer, so it can make a better decision the next time round.
Control of the adaptive optimizations has altered in See here. Cardinality feedback was introduced in Oracle Database 11g Release 2. When the optimizer generates an execution plan mcgrath ymca childwatch hours presence of missing statistics, stale statistics, complex predicates or complex operators may trigger the optimizer to monitor the cardinality of operations in the plan.
Once the execution is complete, if there is a significant difference between the estimated and actual cardinalities, the actual cardinalities are stored in the SGA for later use and the statement is marked as reoptimizable. On next execution the statement is reoptimized using the stored cardinalities, allowing a better plan to be determined.
Cardinality feedback is statement specific and is lost if the instance is restarted or the statement is aged out of the shared pool. In Oracle Database 12c, cardinality feedback has been renamed to statistics feedback. The following code creates a pipelined table function to allow us to demonstrate statistics feedback.
We know the optimizer always estimates the cardinality of pipelined table functions based on the database block size, so we can expect an incorrect estimate of the cardinality of a query against the pipelined table function. The following query returns 10 rows, but the optimizer estimates rows. If we run the statement again, we can see a more accurate cardinality estimate and a note telling us statistics feedback was used. Notice also the change in the value of the child number.
The documentation suggests the detection of cardinality misestimates will also result in the production of SQL plan directives see last paragraph of point 1which myself and others have misunderstood as meaning statistics feedback is persisted in the SQL plan directive. Collection iterator pickler fetch oracle 11g can check for the presence of SQL plan directives as follows. As we can see, in this case no SQL plan directives were created.
We will discuss this point a little more later. In this case, the optimizer decides if a statement should run in parallel and what degree of parallelism DOP is appropriate. On completion, the actual performance of the statement is compared to the estimated performance from the initial optimization phase.
If there is a significant difference between them, the actual performance statistics are stored as statistics feedback and the statement is marked as reoptimizable. Collection iterator pickler fetch oracle 11g next collection iterator pickler fetch oracle 11g the statement is executed the statistics feedback is used to select a more appropriate DOP.
This section is mostly speculation, based on my experience of using statistics feedback and speaking with others. Sachtler video 14 spreeder am not a optimizer developer, so I can not guarantee the following information is true. If I get any evidence to the contrary I will happily post it here.
I previously made the statement that statistics feedback does not get persisted as SQL plan directives. Although that seems to be true, the situation is a little more subtle. Statistics feedback is an indication that the optimizer has made a bad choice.
Typically these bad choices are because it is missing vital information when deciding on an execution plan. Statistics feedback can be used to feed back into the reoptimzation, but it doesn't actually solve the initial problem. The base statistics are still not representative! SQL plan directives are "extra notes" that can prevent the optimizer making the same mistakes in future.
The example in this article uses a pipelined table function to demonstrate statistics feedback. Dynamic sampling of a pipelined table function is a really bad idea, as it will query the pipelined table function once to get the cardinality estimate, then again to process the actual statement.
As a result, creating collection iterator pickler fetch oracle 11g SQL plan directive that suggests dynamic sampling of a pipelined table function would be a really bad idea and it seems the optimizer team have avoided this situation, which is good.
So what am I saying here? Well, a situation that requires the use of statistics feedback may also result in the creation of a SQL plan directive, but that doesn't mean the SQL plan directive contains a persisted version of the statistics feedback. If it were as simple as statistics feedback being persisted as sql plan directives, we would expect it to work for pipelined table functions too.
There seem to be some interesting interactions between statistics feedback and SQL plan directives when they are both collection iterator pickler fetch oracle 11g as a result of cardinality misestimates. Since SQL plan directives are only persisted periodically, this means the reoptimization you get could be totally different depending on how long you wait between the first and second execution of the SQL statement, making the outcome rather unpredictable.
OraFAQ Forum: SQL & PL/SQL » COLLECTION ITERATOR PICKLER FETCH
The latest release of the Oracle Database is here. Check out the new features here Question and Answer Thanks for the question, sarayu. This question is Whilst you are here, check out some content from the AskTom team: Equi-sized partitions on random data. Check out the new features here.
Question and Answer. Whilst you are here, check out some content from the AskTom team: Latest Followup. I am giving the following query: Thank you very much Sarayu K. Now, it would seem the query you explained was the one you just ran! Two ways to do this, first, just empty your plan table and just use display: Write a Review. I still love this name: A reader. Roly porter funkysouls s from India.
B6 AND: Regards Nikhil B. So are we saying it gonna cause performance overhead?. Hope i am not bothering you too much. November 30, - 1: I read collection iterator pickler fetch oracle 11g thread where you said "use hints as tigo pesa application last resort".
However, I ran into a tuning issue that required a hint to solve and want to know if you think I could possibly solve this without a hint. The issue: The output parameter is a ref cursor. Hence, the unique index would be the best way to service the query.
The problem - the cost of the full table scan is lower than the cost of a unique scan, so the CBO goes with the full collection iterator pickler fetch oracle 11g scan. Hence, performance is very slow. I believe the reason the second explain plan has such a high cost is because the CBO wrongly assumed that the table function would return a large number of rows.
Thus, I rewrote the query with the cardinality hint to reflect the usual number of id's passed from the jsp: Can I fix this problem without using either the index hint or the cardinality hint? Shauna Johnson from Vancouver, WA. I've often looked to your site to answer challenging questions, and it is an invaluable resource so thank you!
I looked through the threads and I'm sure the postings are relevant, but I felt it never answered the root of the issue. When I did a show autot, I found that it was set to autotrace on the explain plan. It was enabled still after previous executions of it.
In the labs I'm doing, it's one or the other - either use a trace or an Explain Plan. I know this is an old post, collection iterator pickler fetch oracle 11g I found my way here by researching the issue so I thought I'd add this in case it comes up again for someone.
Thanks, Shauna. Javier from Reston, VA. Based on our execution plans and trace files, we see this operation when querying access restricted tables. This, of course, is expected and is done as a hash join against the results returned by the function. The function is then called as many times as the nested loop operation runs. Where a report might take a couple seconds, it will take minutes to complete because the function collection iterator pickler fetch oracle 11g called thousands of times.
These reports are very long and complex but below collection iterator pickler fetch oracle 11g a sample where I forced the nested loop query takes too long without additional predicate. I am not the developer of these reports but I am doing my best to help them tune it. I can force them to use hash joins and the query time is excellent. There are, unfortunately, thousands of these reports with varying degrees of performance degradation because of this function and developers are wondering if there are other alternatives.
Is there a way to tell the optimizer to use hash joins when dealing with this funciton? Thoughts greatly appreciated. Vikas Chopkar from India. HiPlease guide me Whether table function will improve performance or degrade the performance. As from some website i came to know that Table function is good for OLTP system and Push the data as soon as it get single row to Frontend. Please help me in clearing the confusion.
Regards Vikas Chopkar. More to Explore. Dev Gym Classes, workouts and quizzes on Oracle Database technologies. Expertise through exercise!
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|MANGA ER GOOGLE PLAY||The below is from Thoughts greatly appreciated. Email required Address never made public. Control of the adaptive optimizations has altered in For discussions of variable in-lists as a technique, see this article by William Robertson and binding in-lists in 10g on oracle-developer.|
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