CMP (Clustered Multi-Processing) allows BIG-IP system to utilize multiple CPU cores (TMMs) for better performance and scalability.

Some iRule statements can break CMP by forcing the connection to be handled by a single TMM, which demotes the virtual server from using CMP. These are called CMP-incompatible operations.



set ::foo 123 demotes CMP

:: is used to reference global variables in iRules.



Using global variables (like ::foo) introduces shared memory access across TMMs, which requires serialization.



As a result, CMP is disabled to maintain consistency.



So, using set ::foo 123 causes the virtual server to be CMP-incompatible.