Our intent with this case study is not to provide a comprehensive reference to the trace file, but rather to show how this trace file is used by Oracle engineers. The rows and blocks estimate is the same, and the bytes estimate is slightly different. The first trace file has a continuation message on to the second:. Along the way, we will also gain insight into how the Cost Based Optimizer CBO arrives at the cost for a query and, ultimately, how it arrives at the execution plan. By continuing to use this website, you agree to their use. To view the Case Study Index, click here. RSS feed for comments on this post.
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 Performance — H. I want a random trace file identifier, and I want a random identifier somewhere in my statement. I could keep adding bullets to the list, but I think you get the point: In short, SQLT collects all the diagnostics listed above and a lot more.
Email Address never made public. 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. Many of us have seen this kind of question, and many of us have good hunches.
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Directly related to the cluster factor below. Dynamic sampling tells analzing nothing about the number of bytes per row. The plan hash value in both cases is The SQL text was exactly the same in both runs:.
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Little experience with the subject matter Case Study Abstract This case study uses a tracefile from an actual service request to illustrate a methodology for analyzing trace files. I expect this pilot session to fill out fast. The statements are unique, so each one was analyziing parsed. The first session of this workshop is scheduled for November in Dallas, Texas.
Scripts for trace 10053
The dynamic sampling query only finds the row count. This trace event is not documented, but from a search on google you can find analtzing good resources easily.
The first trace file has a continuation message on to the second: Again, there are two trace files. To view the Case Study Index, click here. Notice also the trace file continuation message from file A to file B: The second trace file is not there because I did not force a hard parse on the second statement execution.
Trace can be used to find out why the optimizer made its decisions. About half the time is dedicated to short guided labs, while the other half uses presentations and demos. Notify me of new posts via email.
Oracle Database – Trace File to understand the Optimizer (CBO) [Gerardnico]
It is also important to point out that the algorithms used by the CBO to estimate the cost of a query may change from version to version as well. I tried to create a tracce 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. So this may not be accurate if the SQL has binds and bind peeking is enabled. Using this script is a lot easier than remembering the exact syntax, and it makes for an uncluttered main script.
It is available at Amazon and many other retailers. Cost-based query optimization is something we must call the real computer science, a hard thing to do and with every new release Oracle optimizes the code dramatically.
I could keep adding bullets to the list, but I think you get the point: The row length would have to come from the catalog. Each case study contains a skill level rating.
The analysis of the bytes difference follows. Fill in your details below or click an icon to log in: To find out more, including how to control cookies, see here: To find out more, including how to control cookies, see here: Written by Carlos Sierra April 19, at