Archive for the ‘Performance’ Category

Automatic DB_FILE_MULTIBLOCK_READ_COUNT

Thursday, August 14th, 2008

Note: Originally this experiment was from a post I wrote on the Oracle Forum: Database - General. I recommend that you read Jonathan Lewis' summarization of the thread instead of reading all 671 posts (as of today). You will spend much less time and get more out ...

Using Bitmap Indexes Effectively

Thursday, May 29th, 2008

Recently I was reading this thread, "Trying to make use of bitmap indexes" on the Oracle Forum. Before I had finished a working example, Jonathan Lewis had posted his response which was on par with my thoughts. Since this is a topic I see frequently, I thought ...

Null-Aware Anti-Join

Thursday, May 22nd, 2008

Recently someone showed me a query execution plan with an operation of HASH JOIN ANTI NA. At first, it was thought maybe it was a bug and the operation had a type-o in it, but after further research it was discovered it was a valid operation and a new ...

Top Ways How Not To Scale Your Data Warehouse

Monday, April 28th, 2008

Working in the Real-World Performance Group at Oracle has allowed me to see quite a few customers' data warehouses. Unfortunately some customers find their data warehouse suffering from performance problems, not because there is a platform issue, but often because the features are not used or are not used ...

There Is No Time Like ‘%NOW%’ To Use Dynamic Sampling

Wednesday, March 5th, 2008

I recently came across a query in which the Optimizer was making a poor cardinality estimate, which in turn caused inefficient join type, which in turn caused the query to run excessively long. This post is a reenactment of my troubleshooting. The Suspect SQL The original SQL was quite large ...

Oracle 11g: Real-Time SQL Monitoring Using DBMS_SQLTUNE.REPORT_SQL_MONITOR

Sunday, January 6th, 2008

Many times a DBA wants to know where a SQL statement is in its execution plan and where the time is being spent. There are a few ways to find out this information, but an 11g new feature makes gathering this information extremely easy. Oracle 11g Real-Time SQL Monitoring ...

What Are Your System Statistics?

Wednesday, January 2nd, 2008

I've been working on a few test cases and I'm in search of some real-world data. If your production Oracle database uses system statistics, either Workload Statistics or Noworkload Statistics, and you are willing to share them, please post a comment with the output from the following two ...

Oracle Optimizer Development Team Starts A Blog

Wednesday, December 5th, 2007

Since the introduction of the Cost Based Optimizer (CBO) in Oracle 7.0, people have been both fascinated and terrified by it and the statistics that feed it. There has long been a belief that a degree in witchcraft or black magic is required to successfully work with the CBO. ...