When to perform RUNSTATS in DB2 is the prime question in SQL interviews. Here are ideas and examples for you to tell correct answer in your next interview.

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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.

1. When a table is loaded
2. When an index is created
3. When a tablespace is reorganized
4. When there have been extensive updates, deletions, or insertions in a tablespace
5. After the recovery of a tablespace to a prior point in time

How Optimizer Decision Affects When You Not Collect Statistics

1. The optimizer may not take the right decision for multi-joint tables query
2. The optimizer may choose the wrong choice of index, which in turn affects performance
3. 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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