WARNING: Do not use AMM
with Linux Hugepages
28 December 2008
A very common error on Linux platforms is attempting to implement
automatic memory management with the Linux hugepages support.
Oracle does NOT recommend using Automatic Memory Management
(AMM, e.g. setting memory_target) with Linux hugepages.
See MOSC note 749851.1 "HugePages
and Oracle Database 11g Automatic Memory Management (AMM) on Linux"
for important details. The message ORA-00845 addresses this
error:
ORA-00845: MEMORY_TARGET not supported on this
system
Cause: The MEMORY_TARGET parameter was not
supported on this operating system or /dev/shm was not sized
correctly on Linux.
Action: Refer to documentation for a list of
supported operating systems. Or, size /dev/shm to be at least the
SGA_MAX_SIZE on each Oracle instance running on the system.
AMM is a memory-morphing tool that adjusts the sizes of the SGA
pool reactively, as workloads change. It works well on tiny
systems, but for large databases, the DBA can perform the
SGA pool size
adjustment proactively, before a workload change cripples
performance.
In sum, AMM is not compatible with Linux Hugepages.
Also, beware that
AMM re-size operations can cripple Oracle performance in some
cases.
For mission-critical databases, I recommend building intelligent SGA
monitors that predict workload changes before they occur and change
the SGA just-in-time. For complete details, see my book
Oracle
Tuning: The Definitive Reference.
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