PRE_PAGE_SGA can increase the process startup duration, because every process that starts must access every page in the SGA. The cost of this strategy is fixed; however, you might simply determine that 20,000 pages must be touched every time a process starts. This approach can be useful with some applications, but not with all applications. Overhead can be significant if your system frequently creates and destroys processes by, for example, continually logging on and logging off.
The advantage that PRE_PAGE_SGA can afford depends on page size. For example, if the SGA is 80 MB in size and the page size is 4 KB, then 20,000 pages must be touched to refresh the SGA (80,000/4 = 20,000).
If the system permits you to set a 4 MB page size, then only 20 pages must be touched to refresh the SGA (80,000/4,000 = 20). The page size is operating system-specific and generally cannot be changed. Some operating systems, however, have a special implementation for shared memory whereby you can change the page size.
这个参数不单会导致启动的时候变慢,而且会导致建立连接的时候变慢,9i的某些版本可能因为bug导致这个参数没有起到作用
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