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ASMM and LINUX x86-64 Hugepages Support [ID 1134002.1]

原创 Linux操作系统 作者:spider0283 时间:2011-09-04 00:43:45 0 删除 编辑

修改时间 20-JUN-2011     类型 HOWTO     状态 PUBLISHED 

In this Document
  Goal
  Solution
  References


Applies to:

Oracle Server - Enterprise Edition - Version: 10.2.0.1 to 11.2.0.2 - Release: 10.2 to 11.2
Linux x86-64
This pertains to oracle 10.2 database instances on LINUX x86-64 bit systems running ASMM (i.e. SGA_TARGET with SGA_MAX_SIZE)

Goal

This document explains the supportability of LINUX HUGEPAGES on Oracle 10.X database instances running with Automatic Shared Memory Management (ASMM) and contrasts this to the documented limits of AMM usage with LINUX HUGEPAGES on version 11.X database instances.

Solution

Due to some misunderstandings in the supportability of LINUX HUGEPAGES with LINUX x86-64 bit running with ASMM (version 10g feature) enabled I am writing this note to consolidate the information on the topic.

1.  Unpublished Bug 6781280 Describes the issue as follows:

 For 11g on Linux if you want to use Linux hugepages (which is recommended in 
 most cases), then you cannot use the 11g new feature Automatic Memory 
 Management. From the 11g Administrator's guide:
 ___
 Automatic Memory Management (AMM) is the simplest way to manage instance 
 memory is to allow the Oracle Database instance to automatically manage and 
 tune it for you. To do so (on most platforms), you set only a target memory 
 size initialization parameter (MEMORY_TARGET) and optionally a maximum memory 
 size initialization parameter (MEMORY_MAX_TARGET). The instance then tunes to 
 the target memory size, redistributing memory as needed between the system 
 global area (SGA) and the instance program global area (instance PGA).
 ---
 If AMM is enabled and Linux hugepage's are enabled as well, then AMM will 
 override Linux hugepage's usage.

 The AMM feature is not to be confused with Automatic Shared Memory Management 
 (ASMM) which was introduced in 10g. ASMM along with the PGA_AGGREGATE_TARGET 
 database parameter will automatically manage the SGA memory and the PGA 
 memory and does not conflict with Linux hugepage's. Thus, if you want to use 
 Linux hugepage's and automatically manage database memory then using ASMM is 
 the workaround.

2.  The oracle documentation for 11.2 explains the hugepages memory limitations with AMM:

Oracle® Database Administrator's Reference
11g Release 2 (11.2) for Linux and UNIX-Based Operating Systems
Part Number E10839-14

G.2.3 Restrictions for HugePages Configurations

Following are the limitations of using HugePages:

*

The Automatic Memory Management (AMM) and HugePages are not compatible. With AMM the entire SGA memory is allocated by creating files under /dev/shm. When Oracle Database allocates SGA that way HugePages are not reserved. You must disable AMM on Oracle Database 11g to use HugePages.
*

If you are using VLM in a 32-bit environment, then you cannot use HugePages for the Database Buffer cache. HugePages can be used for other parts of SGA like shared_pool, large_pool, and so on. Memory allocation for VLM (buffer cache) is done using shared memory file systems (ramfs/tmpfs/shmfs). HugePages does not get reserved or used by the memory file systems.
*

HugePages are not subject to allocation or release after system startup, unless a system administrator changes the HugePages configuration by modifying the number of pages available, or the pool size. If the space required is not reserved in memory during system startup, then HugePages allocation fails.


Note:

As ramfs does not provide the necessary functionality to support memory target, Automatic Memory Management is not supported when ramfs is used to mount /dev/shm. 


Note:

Oracle recommends that you unset MEMORY_TARGET parameter, before implementing Very Large Memory on the same system. 

SUMMARY
=========

ASMM is supported with LINUX x86-64 Hugepages but AMM is not supported with Hugepages.



References

BUG:9358381 - ASM INSTANCE IS CRASHING AS ORA-600[KGHLKREM1] WHEN HUGEPAGES ARE IN USE
NOTE:361468.1 - HugePages on Oracle Linux 64-bit
NOTE:749851.1 - HugePages and Oracle Database 11g Automatic Memory Management (AMM) on Linux

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产品
  • Oracle Database Products > Oracle Database > Oracle Database > Oracle Server - Enterprise Edition
关键字
ASMM; AUTOMATIC SHARED MEMORY MANAGEMENT; HUGEPAGES; LINUX; DYNAMIC ADV FEATURES

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