Deciding whether to rebind after you collect statistics

You do not always need to rebind all applications after you gather statistics.

About this task

You might need to rebind applications after you collect statistics. This action is required only if the access path statistics changed significantly after you last bound the applications and performance suffers as a result. However, it is best to rebind applications during migration DB2® to a new version, to generate new run time structures. You can specify the APREUSE bind option to specify that DB2 generates new run time structures but tries to reuse existing access paths.

When performance degrades to an unacceptable level, take any of the following actions:

• Analyze the statistics that are described in the recommendations in this information to help you develop your own guidelines for when to rebind.
• In most cases, rebind applications when the following conditions occur:
  • CLUSTERRATIOF changes to less than 80% (a value of 0.80).
  • NLEAF changes more than 20% from the previous value.
  • NLEVELS changes (only if it was more than a two-level index to begin with).
  • NPAGES changes more than 20% from the previous value.
  • NACTIVEF changes more than 20% from the previous value.
  • The range of HIGH2KEY to LOW2KEY range changes more than 20% from the range previously recorded.
  • Cardinality changes more than 20% from previous range.
  • Distribution statistics change most of the frequent column values, or a new value appears in the frequently occurring values.