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.



Oracle Database Online Documentation 11g Release 2 (11.2) / Database Administration / G Very Large Memory and HugePages

Oracle Database Online Documentation 12c Release 1 (12.1) / Database Administration / G.1 Overview of HugePages

About the author

maciej tokar
Maciej Tokar

An Oracle technology geek and crazy long distance runner, DBA24 Owner
Senior Oracle DBA / Consultant / [OCP10g, OCP12c, OCE RAC 10g] / [experience: 9y+]
Currently working for Bluegarden (Oslo Norway) by Miratech Group
Past: Mastercard / Trevica by Britenet, Citi International PLC, PZU

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