Groby Computers Ltd - Leicester
Oracle Database Administration
Histograms - index selectivity and how to calculate ix_sel
When the data in an indexed column is strongly skewed, it makes sense to use a histogram to help the optimzer
determine an appropriate cardinality and hence a sensible execution plan.
But sometimes, despite the presence of a useful histogram, you find that the database is running a plan that
is far from sensible. In these cases it can be useful to determine the index selectivity in order to work
out what is going on.
Page Updated Thu Oct 13 21:43:39 BST 2011
