Oracle® Database Administrator's Reference 10g Release 2 (10.2) for UNIX-Based Operating Systems Part Number B15658-03 |
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This appendix contains information about administering Oracle Database on Solaris.
On Solaris systems, Oracle Database uses Intimate Shared Memory (ISM) for shared memory segments because it shares virtual memory resources between Oracle processes. ISM causes the physical memory for the entire shared memory segment to be locked automatically.
On Solaris 8 and Solaris 9 systems, dynamic/pageable ISM (DISM) is available. This enables Oracle Database to share virtual memory resources between processes sharing the segment, and at the same time, enables memory paging. The operating system does not have to lock down physical memory for the entire shared memory segment.
Oracle Database automatically selects ISM or DISM based on the following criteria:
Oracle Database uses DISM if it is available on the system, and if the value of the SGA_MAX_SIZE
initialization parameter is larger than the size required for all SGA components combined. This enables Oracle Database to lock only the amount of physical memory that is used.
Oracle Database uses ISM if the entire shared memory segment is in use at startup or if the value of the SGA_MAX_SIZE
parameter is equal to or smaller than the size required for all SGA components combined.
Regardless of whether Oracle Database uses ISM or DISM, it can always exchange the memory between dynamically sizable components such as the buffer cache, the shared pool, and the large pool after it starts an instance. Oracle Database can relinquish memory from one dynamic SGA component and allocate it to another component.
Because shared memory segments are not implicitly locked in memory, when using DISM, Oracle Database explicitly locks shared memory that is currently in use at startup. When a dynamic SGA operation uses more shared memory, Oracle Database explicitly performs a lock operation on the memory that is put to use. When a dynamic SGA operation releases shared memory, Oracle Database explicitly performs an unlock operation on the memory that is freed, so that it becomes available to other applications.
Oracle Database uses the oradism
utility to lock and unlock shared memory. The oradism
utility is automatically set up during installation. It is not required to perform any configuration tasks to use dynamic SGA.
Note:
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