Check your hints carefully

Back in 2017 I wrote about how I had to disable the result cache after upgrading a database to 11.2.0.4. This week I found one of our top queries and it looked like removing the result cache hints made it run 10 times faster. But this did not make sense because I disabled the result cache. Then I examined the hints closer. They looked like this:

/*+ RESULT CACHE */

There should be an underscore between the two words. I look up hints in the manuals and found that CACHE is a real hint. So, I tried the query with these three additional combinations:

 
/*+ RESULT */
 
/*+ CACHE */
 
/*+ RESULT_CACHE */

It ran slow with the original hint and with just the CACHE hint but none of the others. So, the moral of the story is to check your hints carefully because they may not be what you think they are.

Bobby

About Bobby

I live in Chandler, Arizona with my wife and three daughters. I work for US Foods, the second largest food distribution company in the United States. I have worked in the Information Technology field since 1989. I have a passion for Oracle database performance tuning because I enjoy challenging technical problems that require an understanding of computer science. I enjoy communicating with people about my work.
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