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|Oracle Solaris Tunable Parameters Reference Manual Oracle Solaris 11 Information Library|
System V shared memory allows the creation of a segment by a process. Cooperating processes can attach to the memory segment (subject to access permissions on the segment) and gain access to the data contained in the segment. This capability is implemented as a loadable module. Entries in the /etc/system file must contain the shmsys: prefix..
A special kind of shared memory known as intimate shared memory (ISM) is used by DBMS vendors to maximize performance. When a shared memory segment is made into an ISM segment, the memory for the segment is locked. This feature enables a faster I/O path to be followed and improves memory usage. A number of kernel resources describing the segment are then shared between all processes that attach to the segment in ISM mode.
5 percent of available system memory when the first ISM segment is created
0 to 50 percent of physical memory
None. Values that are too small can cause the system to hang or performance to severely degrade when memory is consumed with ISM segments.
On database servers with large amounts of physical memory using ISM, the value of this parameter can be decreased. If ISM segments are not used, this parameter has no effect. A maximum value of 128 MB (0x4000) is almost certainly sufficient on large memory machines.