Oracle USE_LARGE_PAGES初始化參數

這篇文章討論Oracle數據庫初始化參數use_large_pages的使用。

SQL> show parameter use_large_pages

NAME TYPE

 

VALUE

 

use_large_pages string

TRUE

在11gR2版本的數據庫，use_large_pages的默認值是TRUE。

SQL> alter system set use_large_pages=xxx scope=spfile;

alter system set use_large_pages=xxx scope=spfile

*

第 1 行出現錯誤:

ORA-00096: 值 XXX 對參數 use_large_pages 無效, 它必須來自 FALSE, ONLY, AUTO,TRUE 之間

use_large_pages可設置的值包括：FALSE，ONLY，AUTO，TRUE。

下面經過摘取官方文檔討論ONLY和TRUE之間的區別：

5.1.9 Use Automatic Shared Memory Management and Avoid Memory Paging

For any systems with 4 GB or more memory, disable Automatic Memory Management by setting MEMORY_TARGET=0 and enable Automatic Shared Memory Management by setting SGA_TARGET.

The sum of SGA and PGA memory allocations on the database server should always be less than your system's physical memory, and conservatively should be less than 75% of total system memory. However, PGA_AGGREGATE_TARGET is not a hard limit, and for some Data Warehouse or reporting applications, the PGA memory can grow to be 3 X PGA_AGGREGATE_TARGET.

Monitor PGA memory and host-based memory utilization using OracleEnterprise Manager, or by querying v$pgastat and operating systems statistics, to get an accurate understanding of memory utilization.

Avoid memory paging by adjusting the number of databases and applications, or reducing the allocated memory settings.

On Linux Operating systems it is recommended that you configure HugePages so that ASM and database instances can use it for their SGA.

在Linux操做系統推薦配置HugePages，以致於ASM和數據庫實例的SGA都能使用HugePage來提升性能。ASM實例的SGA一樣有必要使用HugePage來提升性能。

HugePages is a feature integrated into the Linux kernel from release 2.6. This feature provides the alternative to the 4K page size providing bigger pages. Using HugePages has the benefit of saving memory resources by decreasing page table overhead while making sure the memory is not paged to disk. This contributes to faster overall memory performance. Next to this overall node stability will benefit from using HugePages.

Ensuring the entire SGA of a database instance is stored in HugePages can be accomplished by setting the init.ora parameter use_large_pages=only. Setting this parameter will ensure that an instance will start only when it can get all of its memory for SGA from HugePages. For this reason the settinguse_large_pages=only is recommended for database instances.

設置初始化參數中的use_large_pages=only可以確保數據庫實例的整個SGA存放在HugePages中。設置這個參數將確保只有當數據庫實例的SGA從HugePages中得到全部的內存才能被啓動。基於這個緣由，use_large_pages=only是數據庫實例推薦的設置。

For ASM instances leave use_large_pages=true (the default value). This setting still ensures that HugePages are used when available, but also ensures that ASM as part of Grid Infrastructure starts when HugePages are not or insufficiently configured.

針對ASM實例，保留use_large_pages=true（默認值），這個設置確保在Hugepage活動的狀況下仍然可以使用，可是也確保當HugePages不活動或者沒有足夠配置的狀況下，做爲GI一部分的ASM可以被啓動。

Use Automatic Shared Memory Management, as HugePages are not compatible with Automatic Memory Management.

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