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This is a question for developers while working on projects and when they give interviews. Runstats is a utility that collects statistics and sends these to the optimizer for the right decision.
When to Run Runstats in DB2
You need to run this utility during the below scenarios.
- When a table is loaded
- When an index is created
- When a tablespace is reorganized
- When there have been extensive updates, deletions, or insertions in a tablespace
- After the recovery of a tablespace to a prior point in time
How Optimizer Decision Affects When You Not Collect Statistics
- The optimizer may not take the right decision for multi-joint tables query
- The optimizer may choose the wrong choice of index, which in turn affects performance
- When a column designed to have default values, you need to run the RUNSTATS utility for frequency value statistics help in better decision
How to Know When to Execute Runstats
- You need to refer to SYSIBM.SYSCOLDIST catalog table about the running of Runstats utility is needed or not. The IBM Data Studio tool will also show those statistics.
- DB2 gets the frequency value of statistics when Runstats utility is executed.
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