I could have also forced a hard parse by placing the random string in a comment:. The collected files can be reviewed, analyzed, and compared. 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. The is typically not the best place to start looking for tuning opportunities – the execution plan and TKProf have better information in this regard; the is used for deeper cause determination. 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. Notice also the trace file continuation message from file A to file B:
More important, the state of the system changes overtime, so you may need to re-collect the same diagnostics more than once. The dynamic sampling query only finds the row count. If you want to actually find root causes before trying to fix your SQL, you may want to collect relevant diagnostics. Each case study contains a skill level rating. Allowing number digits per byte, each row would return 21 bytes. Here is a one-line script for starting the trace The first trace file has a continuation message on to the second:
Our task here is to analyze the bad plan and determine how the CBO computed the costs that led analgzing the cheaper, but flawed plan.
Analyzing Trace Files. The will help answer the question “Why was my index not used?
Case Study: Analyzing Trace Files by Jennifer Panqueva on Prezi
To get a trace file split into pieces, change the trace file identifier. Analyzing Trace Files https: Fill in your fipes below or click an icon to log in: One way to force a hard parse is to vary the SQL with a random identifier.
Please provide your feedback on the case studies or suggest case study topics by emailing the Global Knowledge Management Team. The list is large, but I will enumerate some of the studu important pieces: Oracle Support Case Studies are written by support engineers who work with customers on a daily basis.
fikes Living in Seattle, WA. These SQL text variations were made manually with an editor. Still I think our eagerness to help blinds us a bit.
The right thing to do is to step back and analyze the facts, and I mean all the diagnostics supporting the observation. So lets enjoy it: Notify me of new comments via email. The Case study program is no longer in existence. When time permits, I do volunteer to help on an analysis. The plan hash value in both cases is In short, SQLT collects all the diagnostics listed above and a lot more. Trace can be used to find out why the optimizer made its decisions. Leave a Reply Cancel reply Enter your comment here Conclusion This blog post made the following points about the trace technique: To get trace output, is necessary to force a hard parse.
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. The simplified dynamic sampling query is:.
analyzinh You are commenting using your Facebook account. Fill in your details below or click an icon to log in: Stelios Charalambides has done an excellent job writing a book on this topic.
Optimizer debug trace event, trace file The trace file we produce has tracr of information as expected; all session optimizer parameter values and every table, index and possible access path statistics etc. Written by Carlos Sierra September 2, at 5: I could have also forced a hard parse by placing the random string in a filss. The is typically not the best place to start looking for tuning opportunities – the execution plan and TKProf have better information in this regard; the is used for deeper cause determination.
Scripts for trace 10053
About half the time is dedicated to short guided labs, while the other half uses presentations and demos. I want a random trace file identifier, and I want a random identifier somewhere in my statement. A user must have been granted alter session before running trace