Restrictions on HIGH2KEY and LOW2KEY statistics

When you collect the HIGH2KEY and LOW2KEY statistics for a Db2® nickname, the information for some columns is not collected.

About this task

Restrictions

When a wrapper creates a nickname on a remote table or nickname, the wrapper collects the HIGH2KEY and LOW2KEY statistics only for numeric columns, and only when the column cardinality is greater than 3.

Procedure

To collect HIGH2KEY and LOW2KEY statistics, use either of the following methods:

Procedure

  • Use SYSPROC.NNSTAT with the METHOD parameter set to 2. This setting specifies data-based statistics collection. The data-based method queries data from the remote table to calculate the values for local statistics. This method, however, can use significant resources at the remote server and the federated server.
  • Issue the SQL UPDATE statement to update the HIGH2KEY and LOW2KEY columns in the SYSSTAT.COLUMNS view. In this case, you must manually determine the correct values for HIGH2KEY and LOW2KEY.