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Oracle by Guy Harrison

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Chapter 19. Optimizing PGA Memory

The System Global Area (SGA) is an area of shared memory; all Oracle sessions can read and write from this common memory space. In contrast, the Program Global Area (PGA) represents private memory that each server process uses for maintaining temporary work areas, program stack, and variables.

The SGA includes the buffer cache, which serves to reduce disk IO by caching data blocks in memory. Sessions can avoid reading from disk if the required data block is present in the cache. The PGA serves an equally important, though possibly less recognized, role in reducing IO. Most nontrivial SQL processing employs temporary work areas to support intermediate result sets, hash join areas, and sorts. We looked at these ...

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