Oracle中db_16k_cache_size的设定测试 


参考：http://blog.chinaunix.net/uid-23622436-id-3234873.html


官方文档：http://docs.oracle.com/cd/E11882_01/server.112/e40402/initparams046.htm#REFRN10027


创建非标准块表空间，需要设置db_nk_cache_size值后，方可创建表空间。
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.




1、以创建16K的表空间块为例，db_16k_cache_size初始为0，创建表空间失败。


SYS@PROD3> show parameter block


NAME     TYPE VALUE
------------------------------------ ----------- ------------------------------
db_block_buffers     integer 0
db_block_checking     string FALSE
db_block_checksum     string TYPICAL
db_block_size     integer 8192
db_file_multiblock_read_count     integer 128
SYS@PROD3> show parameter 16k


NAME     TYPE VALUE
------------------------------------ ----------- ------------------------------
db_16k_cache_size     big integer 0




SYS@PROD3> show parameter db_create_file_dest


NAME     TYPE VALUE
------------------------------------ ----------- ------------------------------
db_create_file_dest     string /u01/app/oracle/oradata/PROD3


SYS@PROD3> create tablespace tb16 datafile size 10m blocksize 16k;
create tablespace tb16 datafile size 10m blocksize 16k
*
ERROR at line 1:
ORA-29339: tablespace block size 16384 does not match configured block sizes


2、修改db_16k_cache_size参数值后，创建表空间成功；
SYS@PROD3> alter system set db_16k_cache_size=20m;
SYS@PROD3> create tablespace tb16 datafile size 10m blocksize 16k;
SYS@PROD3> create table table16 tablespace tb16 as select * from dba_objects ;


3、重新将该db_16k_cache_size设置为0，数据插入失败。


SYS@PROD3> alter system set db_16k_cache_size=0;
SYS@PROD3> show parameter 16


NAME     TYPE VALUE
------------------------------------ ----------- ------------------------------
db_16k_cache_size     big integer 0




SYS@PROD3> insert into  table16  select * from dba_objects ;
insert into  table16  select * from dba_objects
             *
ERROR at line 1:
ORA-00379: no free buffers available in buffer pool DEFAULT for block size 16K


4、db_16k_cache_size参数值默认是0，设置后最小值为系统CPU数*4M，最大值取决于db_buffer值；






SYS@PROD3> alter system set db_16k_cache_size=1m;
SYS@PROD3> show parameter 16k


NAME     TYPE VALUE
------------------------------------ ----------- ------------------------------
db_16k_cache_size     big integer 8M




官方文档中该参数说明；
http://docs.oracle.com/cd/E11882_01/server.112/e40402/initparams046.htm#REFRN10027
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.



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