Shared-memory Overflow Size (-Mxs)

Database Administration

Reference : Database Startup Parameters : Alphabetical listing of database startup parameters : Shared-memory Overflow Size (-Mxs)

Operating system and syntax	UNIX / Windows	-Mxs n
Use with	Maximum value	Minimum value	Single-user default	Multi-user default
DBS	System dependent¹	1	–	For 32-bit platforms: 16384 + (# of users * 300) / 1024 For 64-bit platforms: 16384 + (# of users * 400) / 1024

¹ The maximum is limited only by the size of the signed integer data type on the system.

The size of the shared-memory overflow area in kilobytes.

Use Shared-memory Overflow (-Mxs) to replace the default value of the shared-memory overflow area; it does not increase it. The overflow area is appended to the shared-memory area. If the overflow area is too small, the database engine exits with the following message:

SYSTEM ERROR: Out of free shared memory. Use -Mxs to increase.

Depending on the operating system, the database engine rounds the shared-memory area size to the next 512-byte or 4K boundary.

Note: Validations using -Mxs can be run online as part of routine health checks. For more information, see PROUTIL Utility.

Specific memory requirements when using mandatory fields

If you are using mandatory fields, your approximate memory requirements should consider the following when calculating the value of Shared Memory Overflow (-Mxs):

480 byte overhead

48 bytes for each table containing mandatory fields

12 bytes for each mandatory field

When calculating Shared Memory Overflow (-Mxs), add the total number of bytes to the existing default value. For example, if the total memory required for the mandatory field array is 80K, -Mxs must be (80K + 16K + 4K (100 users).

Note: These numbers are approximations, and may change from release to release.