Oracle中db_nk_cache_size的设定

默认的db block是8k, 但当需要使用2k,4k,16k,32k的block size时,就需要设定db_nk_cache_size,其中n是2,4,16或32.

alter system set db_4k_cache_size=20m scope=both;

DB_nK_CACHE_SIZE

Property	Description
Parameter type	Big integer
Syntax	DB_[2 | 4 | 8 | 16 | 32]K_CACHE_SIZE = integer [K | M | G]
Default value	0 (additional block size caches are not configured by default)
Modifiable	ALTER SYSTEM
Range of values	Minimum: 0 (values greater than zero are automatically modified to be either the user-specified size rounded up to the granule size or 4 MB * number of CPUs, whichever is greater) Maximum: operating system-dependent
Basic	No

DB_nK_CACHE_SIZE (where n = 2, 4, 8, 16, 32) specifies the size of the cache for the nK buffers. You can set this parameter only when DB_BLOCK_SIZE has a value other than nK. For example, if DB_BLOCK_SIZE=4096, then it is illegal to specify the parameter DB_4K_CACHE_SIZE (because the size for the 4 KB block cache is already specified by DB_CACHE_SIZE).

Do not set this parameter to zero if there are any online tablespaces with an nK block size.

Operating system-specific block size restrictions apply. For example, you cannot set DB_32K_CACHE_SIZE if the operating system's maximum block size is less than 32 KB. Also, you cannot set DB_2K_CACHE_SIZE if the minimum block size is greater than 2 KB.

当db_nk_cache_size设置过小时, 系统会自动进行调整,所以不用担心.