Stale statistics can slow your system down, because they worsen the accuracy of the optimizer's estimates of selectivity.
Most of the statistics information that
The one piece of information that is not kept up to date is the average
number of duplicates for columns in an index. This statistic is given a default
and then is updated whenever you create an index or update the statistics by
running either the
Statistics are likely to be stale if the number of distinct values in an
index has changed significantly. This can happen often or rarely, depending on
the nature of the column being indexed. You can refresh cardinality statistics
by calling the procedure