Archive for the ‘Statistics’ Category
Wednesday, July 16th, 2008
Previously I blogged about the new and improved DBMS_STATS.AUTO_SAMPLE_SIZE used to calculate NDV in Oracle 11g and now I wanted to touch on another new feature of DBMS_STATS in 11g: Incremental Global Statistics On Partitioned Tables.
Before Incremental Global Stats (Two-Pass Method)
When DBMS_STATS.GATHER_TABLE_STATS collects statistics on a partitioned table, ...
Posted in 11gR1, Data Warehousing, Optimizer, Oracle, Statistics, VLDB | 4 Comments »
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 ...
Posted in 10gR2, 11gR1, Data Warehousing, Execution Plans, Optimizer, Performance, SQL Tuning, Statistics, Troubleshooting, VLDB | 6 Comments »
Wednesday, March 26th, 2008
Recently the Oracle Optimizer Development Team put out a White Paper entitled Upgrading from Oracle Database 9i to 10g: What to expect from the Optimizer. This paper discusses the main differences between 9i and 10g in the subject area of the Optimizer and Statistics. As G.I. Joe ...
Posted in 10gR2, Execution Plans, Optimizer, Oracle, Statistics, Troubleshooting | 16 Comments »
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 ...
Posted in 10gR2, 11gR1, Data Warehousing, Execution Plans, Optimizer, Oracle, Performance, SQL Tuning, Statistics, VLDB | 11 Comments »
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 ...
Posted in 10gR2, 11gR1, Execution Plans, Optimizer, Oracle, Performance, SQL Tuning, Statistics | 29 Comments »
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. ...
Posted in Execution Plans, Optimizer, Oracle, Performance, Statistics, Troubleshooting | 8 Comments »
Wednesday, November 21st, 2007
One of the most common performance issues DBAs encounter are bad execution plans. Many try to resolve bad executions plans by setting optimizer related parameters or even hidden underscore parameters. Some even try to decipher a long and complex 10053 trace in hopes to find an answer. ...
Posted in Execution Plans, Optimizer, Oracle, Performance, SQL Tuning, Statistics, Troubleshooting | 21 Comments »
Monday, November 19th, 2007
Oracle OpenWorld 2007 has come and gone and from the Real-World Performance Group's perspective we'd consider it a successful one. The content of this year's presentations seems to have gone over quite well as shown by the number of hallway comments and emails we received. At least two ...
Posted in Data Warehousing, Execution Plans, Optimizer, Oracle, Performance, SQL Tuning, Statistics, VLDB | 3 Comments »