That’s because it can actually validate the optimizer’s original estimates by running various steps in a given plan and comparing the actual results to the estimates.
When it’s all done, if it has found a better plan, it offers to implement that new plan via a SQL Profile.
Refer to the " Oracle Class Libraries" section in this document for information on the C class libraries provided in this release.
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Since it is allowed as much time as it wants to do it’s analysis, the advisor can sometimes find better approaches.
Those offered Profiles often have a lightly documented hint (OPT_ESTIMATE) that allows it to scale the optimizer estimates for various operations – essentially it’s a fudge factor.
The problem with this hint is that, far from locking a plan in place, it is locking an empirically derived fudge factor in place.
This release is a 32-bit version of Oracle Objects for OLE and will work on Windows NT, Windows 2000 and Windows 98.
Class libraries are provided for Microsoft Visual C versions 6.x.