The index breakpoint seems to be in the area of 1000 rows but note that is
varies for SELECTs and UPDATES/DELETES (as far as the optimizer choices). For
example, the optimizer uses an index for a 1 million row table when about 4% or
less of the rows are being retrieved, but for a 1000 row table it only uses the
index when 1% or less is retrieved on a SELECT ... but ... that same smaller
table uses an index well into 4% for UPDATES/DELETES when the indexed column is
used. If you have the book, I cover the breakpoint on pages 386-389.
Rich Niemiec
Oracle Performance Tips and Techniques, Oracle Press
ISBN: 0078824346
The tuning scripts from the book are at:
http://www.tusc.com/books/perf_tune.html
Received on Fri Jul 09 1999 - 11:49:23 CDT
