Examining Index Pages

In Dynamic Server, when you execute the UPDATE STATISTICS statement in any mode, the database server reads through index pages to:

If pages are found with the delete flag marked as 1, the corresponding keys are removed from the B-tree cleaner list.

This operation is particularly useful if a system failure causes the B-tree cleaner list (which exists in shared memory) to be lost. To remove the B-tree items that have been marked as deleted but are not yet removed from the B-tree, run the UPDATE STATISTICS statement. For information on the B-tree cleaner list, see your IBM Informix Administrator's Guide.

Updating Statistics for Columns of User-Defined Types (IDS)

To collect statistics for a column of a user-defined data type, you must specify either medium or high mode. When you execute UPDATE STATISTICS, the database server does not collect values for the colmin and colmax columns of the syscolumns table for columns that hold user-defined data types.

To drop statistics for a column that holds one of these data types, you must execute UPDATE STATISTICS in the LOW mode with the DROP DISTRIBUTIONS option. When you use this option, the database server removes the row in the sysdistrib system catalog table that corresponds to the tableid and column. In addition, the database server removes any large objects that might have been created for storing the statistics information.