Configuring Additional Shared Memory Identifiers Limit

Starting with 18c, on Oracle Solaris systems, Oracle Database uses a new method of sharing memory among a group of processes, also known as Managed Global Areas (MGA). The operating system memory allocation mechanism for this new method is Optimized Shared Memory (OSM).

Oracle recommends that you configure the additional shared memory identifiers and increase the shared memory limits as follows:

Additional number of MGA segments (project.max-shm-ids) = MGA memory size / granule size


MGA memory size is the cumulative MGA memory requirement size for all processes in an Oracle Database instance. Typically, 2MB per Oracle process.

Minimum value of granule size is 4 MB. For large SGA, granule size may increase automatically upto 512 MB.

Refer to the following table to determine the approximate granule size.

Table B-3 Granule Size for SGA Values

SGA Granule Size
Less than 1 GB 4 MB
Between 1 GB and 8 GB 16 MB
Between 8 GB and 16 GB 32 MB
Between 16 GB and 32 GB 64 MB
Between 32 GB and 64 GB 128 MB
Between 64 GB and 128 GB 256 MB
Greater than 128 GB 512 MB