Thursday, March 11, 2010

Performance tuning basics

Question: I am new to Oracle tuning, and I want to know the steps for Oracle performance tuning.

Answer: As of Oracle 11g, Oracle has codified a top-down tuning approach, with the first steps being very broad, and successive steps becoming more focused. Oracle performance tuning is very complex, and where there are some generic steps for performance tuning, the world is not always that simple. Here are the steps for a top-down Oracle performance tuning approach:

Oracle tuning involves the following steps, with each step getting more specific and targeted:

Server & network tuning—This is always the first step, as not amount of tuning will help a poor server environment.

Instance tuning—Tuning the Oracle SGA is the next step, and all of the Oracle initialization parameters must be reviewed to ensure that the database has been properly configured for it's workload. In some cases, a database may have a bi-modal workload (online vs. batch) and the instance parms are adjusted as-needed during this step.

Object tuning—This step of performance tuning looks at the setting for Oracle tables and indexes. Table and index settings such as PCTFREE, PCTUSED, and FREELISTS can have a dramatic impact on Oracle performance.

SQL tuning—This is last step in tuning, and the most time-consuming tuning operation because there can be many thousands of individual SQL statements that access the Oracle database. If you have carefully optimized the workload as a whole from step 2, there you will only need to tune "outlier" SQL statements. Within this step, there are sub-steps:
Remove unnecessary large-table full-table scans—In this tuning step you evaluate the SQL based on the number of rows returned by the query. Standard b-tree indexes can be added to tables, and bitmapped and function-based indexes can also eliminate full-table scans.

Cache small-table full-table scans—In this step we ensure that a dedicated data buffer is available for the rows.

Verify optimal index usage—This step is critical because you may have "missing" indexes in your database, causing excessive I/O.

Materialize your aggregations and summaries for static tables - One features of the Oracle SQLAccess advisor is recommendations for new indexes and suggestions for materialized views.

Again, this is only a high-level overview of the Oracle performance tuning steps. For complete details on the steps for Oracle performance tuning, see my book "Oracle Tuning: The Definitive Reference".


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  2. I agree that improving the performance of Oracle is not only essential but takes a lot of time and efforts too. I have been assigned to do the same is feeling very stressed with the whole idea as I don't know from where to start. Your post seems to me a ray of hope as I got the idea about from where to start and how to proceed further.
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  3. Hi, Thanks for the article. Can you give some examples for each step.