On Unix, the database server uses swap space and memory to manage the cache size. The swap space is a system-wide resource on most Unix operating systems, but not on all. In this section, the sum of memory and swap space is called the system resources. See your operating system documentation for details.
On startup, the database allocates the specified maximum cache size from the system resources. It loads some of this into memory (the initial cache size) and keeps the remainder as swap space.
The total amount of system resources used by the database server is constant until the database server shuts down, but the proportion loaded into memory changes. Each minute, the database server evaluates cache and operating statistics. If the database server is busy and demanding of memory, it may move cache pages from swap space into memory. If the other processes in the system require memory, the database server may move cache pages out from memory to swap space.
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