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by Craig Shallahamer Get the book here |
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Craig Shallahamer's Blog
The text below is an except from the book, Oracle Performance Firefighting, written by Craig Shallahamer of OraPub, Inc. Figures and tables are not included on this page, only their reference. To order the book in either print or PDF form, click here. ©2009, 2010 by Craig Shallahamer. This is copyrighted material. Please—Out of respect for those involved in the creation of the book and also for their familes, we ask you to respect the copyright both in intent and deed. Thank you. ------------------------------- The CBC is essentially a searching structure. There are many search algorithms for Oracle to choose from, but for reasons I'll detail in Chapter 6, Oracle chose what is known as a hashing structure. Figure 3-5 is an example of a hashing structure. Figure 3-5. A hashing structure can be used to quickly locate (search for) a specific object. The memory chains shown in option A on the left are protected by a single latch, whereas with option B, the chains are protected by three latches. Essentially, a hashing structure is composed of a bunch of chains. When looking for an object (think block buffer or cursor), the searcher is directed to one of the chains. Then the searcher sequentially searches the chain, hoping to find whatever it is seeking. With Oracle's hashing implementation, if the object is not found in the specified chain, then the object is not in the cache. Please—Out of respect for those involved in the creation of the book and also for their familes, we ask you to respect the copyright both in intent and deed. Thank you. |
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