HugePages vs Automatic Memory Management in Oracle Databases


Why are HugePages incompatible with Automatic Memory Management in Oracle Databases?

Just few words to answer this straightforward question:

You cannot use Automatic Memory Management (AMM) while implementing HugePages, because AMM works on dynamic SGA and PGA tuning. For example AMM can unmap the unused SGA space and map it to PGA and back. With HugePages contiguous pages are preallocated and cannot be used for anything else but for System V shared memory (for example, SGA).

When you use AMM, the entire SGA memory is allocated by creating files under /dev/shm. When Oracle Database allocates SGA with AMM, HugePages are not reserved. To use HugePages you must disable AMM.

reference: https://docs.oracle.com/cd/E11882_01/server.112/e10839/appi_vlm.htm#UNXAR385

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