Many of us have seen this kind of question, and many of us have good hunches. Some experience with the subject matter Beginner: In the first execution, statistics had been deleted. The first session of this workshop is scheduled for November in Dallas, Texas. Notify me of new posts via email.
Each case study contains a skill level rating. When time permits, I do volunteer to help on an analysis. Every so often I see on a distribution list a posting that starts like this: Whoops, where is my second trace file? I tried to create a small demostration for a better understanding of this event dump, following script creates a table with a primary key and unique key constraints and the CBO decides to use the unique key constraint over primary key; Code listing For the case of gathered stats, the row length is: The rating provides an indication of what skill level the reader should have as it relates to the information in the case study.
Again, there are two trace files. CLUF Clustering factor of this index; dase measure of how sorted a base table is with respect to this index. Allowing number digits per byte, each row would return 21 bytes.
Oracle Database – Trace File to understand the Optimizer (CBO) [Gerardnico]
It was a real challenge packaging so much info in only two days, 100053 I am very pleased with the result. Oracle Support Case Studies are written by support engineers who work with customers on a daily basis. You are commenting using your Facebook account.
The collected files can be reviewed, analyzed, and compared. Using this script is a lot easier than remembering the exact syntax, and it makes for an uncluttered main script. The trace file we produce has lots of information as expected; all session optimizer parameter values and every table, index foles possible access path statistics etc. By continuing to use this website, you agree to their use.
You are commenting using your WordPress. Trace helps to explain the similarities and differences.
To find out more, including how to control cookies, see here: In the second execution, statistics had been collected. Analyzing Trace Files.
Scripts for trace 10053
A good understanding of SQL processing is essential for writing optimal SQL statements and these trace files help us to understand what happened casee during execution. Directly related to the cluster factor below. The statements are unique, so each one was hard parsed.
I always wondered how and why Oracle optimizer decides to choose one execution plan to other. It simply saves a lot of time!
As everyone else on a distribution list, my first impulse is to make an educated guess permeated by a prior set of experiences. In the first part, Understanding The Fundamental Performance Equation I mentioned the importance of the fundamental performance equation, how to produce SQL Trace files and analyze them with tkprof utulity.
The first trace file has a continuation message on to the second: The SQL text was exactly the same in both runs:. So, if you get to read this, and you want to help yourself while using SQLT but feel intimidated by this little monster, please give it a try and contact me for assistance.
Here is a one-line script for starting the trace Here is file demo. The second trace file is not there because I did not force a hard parse on the second statement execution.
Force a trace file switch by using a random tracefile identifier. Optimizer debug trace event, trace file The trace file we produce has lots of information as expected; all session optimizer parameter values and every table, index and possible access path statistics etc.
Oracle Database – Trace File 10053 to understand the Optimizer (CBO)
Please note that event trace files were designed to assist Oracle developers and support personnel to diagnose optimizer problems and are subject to change with every new patchset ttace release. In the first execution, statistics had been deleted. The rows and blocks estimate is the same, and the bytes estimate is slightly different.
Still I think our eagerness to help blinds us a bit. Significant experience with the subject matter Intermediate: