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Result Cache

Result Cache: when *not* to use it

I encountered recently a case where result cache was incorrectly used, leading to high contention when the application encountered a peak of load. It was not a surprise when I’ve seen that the function was called with an ‘ID’ as argument, which may have thousands of values in this system. I mentioned to the software vendor that the result cache must be used only for frequently calling the function with same arguments, not for random values, even if each value have 2 or 3 identical calls. And, to detail this, I looked at the Oracle Documentation to link the part which explains when the result cache can be used and when it should be avoided.

But I’ve found nothing relevant. This is another(*) case where the Oracle Documentation is completely useless. Without explaining how a feature works, you completely fail to get this feature used. Most people will not take the risk to use it, and a few will use it in the wrong place, before definitely blacklisting this feature.

RESULT_CACHE Hint in 12.1.0.2

Every new Oracle Database patch introduces not only documented features, but also undocumented ones. In this short post I would like to provide information about an enhancement of the RESULT_CACHE hint.

According the documentation, the RESULT_CACHE hint has no parameter. But, as of 12.1.0.2, at least the SNAPSHOT parameter is supported. Its purpose is to specify how much time (in seconds) after the creation the result cache entry has to expire. In other words, you can specify that a specific entry expires even though the objects is based on doesn’t change.

The following example illustrates: