What is update statistics in Informix?
The UPDATE STATISTICS statement converts the old indexes to conform to the newer database server index format and implicitly drops the old indexes. You can convert the indexes table by table or for the entire database at one time. Follow the conversion guidelines in the IBM® Informix® Migration Guide .
How do I check for Informix update statistics?
The type of information you can obtain from the most recent update statistics is the following: The date on which it ran. The mode used (high or medium)…Answer.
| Column | Description |
|---|---|
| resolution | The resolution used by the UPDATE STATISTICS statement |
| confidence | The confidence level used by the UPDATE STATISTICS statement |
What is auto update statistics?
The Auto Update Statistics (AUS) maintenance system identifies tables and indexes that require new optimizer statistics and runs the appropriate UPDATE STATISTICS statements to optimize query performance.
What is the difference between update statistics and update statistics full scan?
“All” statistics means that both “column” and “index” statistics will be updated. “Fullscan” means that to update a statistic, SQL Server will scan 100% of the values in the index or column. That adds up to a lot of IO.
Does update statistics cause blocking?
No, UPDATE Statistics with Full Scan does not cause blocking. It is an online operation i.e. table will be available to read while statistics are updated.
Does update statistics affect performance?
When examining a query execution plan, a large discrepancy between the Actual Number of Rows and the Estimated Number of Rows is an indication of outdated stats. Outdated statistics can lead the optimizer in choosing inefficient execution plans and can dramatically affect overall performance.
How often should you update statistics?
For good database performance with a cost-based optimizer, run the update statistics procedure at least once a week. Run the two step procedure for update statistics on the most important DB2® tables.
How long will update statistics take?
When you run the statement UPDATE STATISTICS to generate a maintenance plan, you may notice that the UPDATE STATISTICS takes a very long time (approximately 24-48 hours) to prepare metadata for large databases.