REGEXP_LIKE runs away when pattern is not found

Question

I am using the following in my pl/sql code:
regexp_like(l_formatted, '^[\_]*([a-z0-9]+(\.|\_*)?)+@([a-z][a-z0-9\-]+(\.|\-*/.))+[a-z]{2,6}$')
It validates e-mail addresses. When the pattern is found (the e-mail is valid) the performance is fine. When the pattern is not found the query takes at least 50 seconds and in a few cases has actually "run away". Has anyone else exprienced this problem?

Answer 1

When the pattern is found (the e-mail is valid) the performance is fine. What's the execution plan?
When the pattern is not found the query takes at least 50 seconds and in a few cases has actually "run away". Are you using Con*Text indexes?
http://www.dba-oracle.com/t_regular_expressions_tuning_index.htm
In some cases you can also index regex with FBI's. But regular expression are notorious for causing full-table scans on multi-million rows tables, and special care must be given to creating matching function-based indexes to keep performance at an acceptable level.
From a performance perspective it’s important to properly index the Oracle tales so that regular expression validation does not cause problematic full-table scans. Oracle syntax allows the use of function-based indexes (FBI’s) to minimize the amount of database I/O associated with a invocation of a regular expression.
Function-based indexes cannot work for all regular expressions, however, and it can be tricky to remove unnecessary full-table scans on some regular expressions, especially regexp_like.
Hope this helps . . .
Donald K. Burleson
Oracle Press author
Author of "Oracle Tuning: The Definitive Reference"
http://www.rampant-books.com/book_2005_1_awr_proactive_tuning.htm