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ISM or DISM Misconfiguration can Slow Down Oracle Database Performance (Doc ID 1472108.1)

Last updated on FEBRUARY 03, 2024

Applies to:

Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Backup Service - Version N/A and later
Oracle Database Cloud Service - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Oracle Database Cloud Exadata Service - Version N/A and later
Information in this document applies to any platform.


Interprocess communication (IPC) is the sharing of data and synchronization of events among processes. Shared memory provides efficient data sharing among multiple processes since data are not required to be moved across multiple process address spaces. Shared memory allows sharing of physical memory pages by multiple processes. That means multiple processes can attach or have mappings to the same physical memory segment. Access to shared memory can be performed by simple pointer dereference in the code. Oracle uses shared memory to cache frequently used data blocks (buffer cache) and to facilitate communication (shared pool) among oracle processes (pmon, smon, dbwr, lgwr, and oracle shadow proceses). Semaphores are used to control concurrency between processes when data in shared memory needs to be modified. See detail.

Oracle Database uses shared memory extensively, Misconfiguration of shared memory during Oracle Database setup can result in lower than expected performance. The goal of this document is to identify those symptoms that lead to slower Oracle Database performance and present solutions to overcome these issues.

Be aware that there might be systems that have different requirements or supported states when it comes to using ISM/ DISM, see for example:

Dynamic Intimate Shared Memory (DISM) is not supported for use on SuperCluster T4-4, T5-8 nor M6-32 Solaris environments



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