PLSQL Function used in where clause - Performance Issue

I have a query which performs quite ok for a limited number of ROWNUMS but once it exceeds this particular ROWNUM it performs very miserable.

Below is the query:

SELECT p.col1,pv.col1 FROM tab1 p, tab2 tv, tab3 pv WHERE myFunc(pv.col1) = 1 AND tv.col1 = pv.col1 AND p.col1 = tv.col2 AND ROWNUM <开发者_JAVA百科 4500

All these tables have huge (more than a million) records.

The above query executes at a very decent speed.

If ROWNUM < 5000 or more then it takes quite a lot of time.

Is there any way I can improve the performance of the above query?

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Check that there is indexes on each join columns on each table, and after that, you can use functional indexes, see for example : http://techonthenet.com/oracle/indexes.php