For the case of gathered stats, the row length is: I expect this pilot session to fill out fast. Written by Carlos Sierra May 8, at 5: You are commenting using your WordPress. Here is how demo.
The first trace file has a continuation message on to the second: The question is WHY? 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 So this may not be accurate if the SQL has binds and bind peeking is enabled.
Whoops, where is my second trace file? Use and events for detail analysis of CBO decisions, changing the value of an optimizer parameter for a […].
To find out more, including how to control cookies, see here: The good plan is basically a shorter version of the bad plan one in which no indexes were considered. This script sets the tracefile identifier to a random string.
Take for example this: The right thing to do is to step back and analyze the facts, and I mean all the diagnostics supporting the observation. There are other ways to force a hard parse, that sometimes work, such as issuing a grant or flushing the statement from the shared pool, if you have the privilege.
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Written by Carlos Sierra Traace 19, at You are commenting using your Twitter account. You are commenting using your WordPress. The dynamic sampling query only finds the row count. The row length would have to come from the catalog. Written by Carlos Sierra September 2, at 5: It simply saves a lot of time! The analysis of the bytes difference follows.
To run tracethe user must be granted alter session. I always wondered how and why Oracle optimizer decides to choose one execution plan to other. A user must have been granted alter session before running trace Notify me of new posts via email.
Scripts for trace 10053
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Because the SQL 10503 different each time, a hard parse is forced each execution. Oracle Support Case Studies are written by support engineers who work with customers on a daily basis.
The Case study program is no longer in existence. I expect this pilot session to fill out fast.
Oracle Database – Trace File 10053 to understand the Optimizer (CBO)
Cost-based trafe 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. Expert About Oracle Support Case Studies Oracle Support Case Studies are created for the purpose of sharing information and for transferring knowledge related to a complex event, process, procedure, or to a series of related events.
As everyone else on a distribution list, my first impulse is to make an educated guess permeated by a prior set of experiences. The second trace file is not there because I did not force trqce hard parse on the second statement execution. A good understanding of SQL processing is essential for writing optimal SQL statements and these trace files help us to understand what happened behind during execution.
The simplified dynamic sampling query is:. It is available at Amazon and many other retailers.