Caching means keeping copies of things that we expect to use soon, and keeping them close by so that we can access them quickly. Chapter 2 described how Oracle changes various types of data blocks (including undo blocks) and showed you a few of the structures that you can see stored in blocks, but it didn’t say anything about how Oracle manages to keep a selection of recently used or popular blocks in memory. Chapter 2 simply assumed that whenever we needed a block, the correct version of that block would be available.
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