The OpenEdge RDBMS uses shared memory to hold database buffers, latches, and control information including the lock table, AI buffers, and BI buffers. On 32-bit systems, the addressable limit is 4 gigabytes, and on 64-bit systems, the addressable limit is 8 terabytes. These limits are architectural limits and are reduced in practice by limitations imposed by the underlying operating system and other factors.

The amount of shared memory allocated for database buffers is specified by the -B startup parameter. The theoretical maximum value for -B is 1,000,000,000 for 64-bit platforms, but in practice, you will never successfully set -B that high.

The maximum number of shared memory segments is 256 on 64-bit systems.

On UNIX, the number of shared memory segments, and their maximum size are constrained by kernel parameters. Fewer large segments tend to give better performance than many small segments.

Note: Actual maximum values are constrained by available system resources and operating system settings. For more information on shared memory segments, see Shared memory segment size (-shmsegsize).