DB_WRITER_PROCESSES与LOG_ARCHIVE_MAX_PROCESSES

DB_WRITER_PROCESSES与LOG_ARCHIVE_MAX_PROCESSES

 

DB_WRITER_PROCESSESLOG_ARCHIVE_MAX_PROC
DB_WRITER_PROCESSES
Property  Description
Parameter type  Integer
Default value  1 or CPU_COUNT / 8, whichever is greater 默认值为1或CPU个数的1/8
Modifiable  No      
Range of values  1 to 20      取值范围为1-20
Basic   No

 

DB_WRITER_PROCESSES is useful for systems that modify data heavily. It specifies the initial number of database writer processes for an instance.

注：DB_WRITER_PROCESSES参数设置DBWn的进程数；由于该参数是静态参数，需要重启数据库。修改该参数值并非越大越好，应根据CPU高峰时的空闲程度进行相应设置，比如：

--对CPU的当前信息采样
[oracle@bldc01 bolan]$ vmstat 5
procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
12  2 862788 111796  92004 29095088    1    1   134   130    0    0 15  1 83  1  0
14  1 862772 116024  91992 29092368    6    0   749  6552 14584 21236 57  3 36  4  0
13  0 862772 136640  92060 29097092    0    0   814  6392 16218 24140 56  4 36  4  0
 9  1 862772 129644  92076 29101512    0    0   692  7062 14918 22074 54  3 38  4  0
15  1 862772 118000  91984 29080072    0    4   577  6216 15478 22928 53  4 39  4  0
10  0 862772 117148  92000 29085192    0    0   692  7029 16265 24344 55  4 37  4  0
13  0 862772 113464  92012 29081772    0    0   676  6954 13775 20328 58  3 35  4  0
--查看当前oracle服务器的CPU个数
SQL> show parameter cpu_count;
NAME         TYPE         VALUE
------------------------------------ -------------------------------- ------------------------------
cpu_count        integer         16
--查看db_writer_processes的参数值
SQL> show parameter db_writer_processes;
NAME         TYPE         VALUE
------------------------------------ -------------------------------- ------------------------------
db_writer_processes       integer         2

 

从上述信息我们发现，CPU的进程数一直维持在12个左右，且频繁出现等待的进程，因此该数据库不适宜调整DB_WRITER_PROCESSES参数。

LOG_ARCHIVE_MAX_PROCESSES
Property  Description
Parameter type  Integer
Default value  2      默认值为2
Modifiable  ALTER SYSTEM     
Range of values  1 to 30      取值范围为1-30
Basic   No

 

LOG_ARCHIVE_MAX_PROCESSES specifies the number of archiver background processes (ARC0 through ARC9) Oracle initially invokes.

The actual number of archiver processes in use may vary subsequently based on archive workload.

注：LOG_ARCHIVE_MAX_PROCESSES参数设置ARCn的进程数，该参数会自动根据数据库的实际情况进行调整。比如：

--查看log_archive_max_processes的参数值
SQL> show parameter log_archive_max_processes;
NAME         TYPE         VALUE
------------------------------------ -------------------------------- ------------------------------
log_archive_max_processes      integer         4
[oracle@bldc01 bolan]$ ps -aux |grep ora_arc
Warning: bad syntax, perhaps a bogus '-'? See /usr/share/doc/procps-3.2.7/FAQ
oracle   20174  0.0  0.0  61184   772 pts/1    S+   15:01   0:00 grep ora_arc
oracle   31910  0.0  0.6 17280616 216552 ?     Ss   Mar01 121:59 ora_arc0_bolan
oracle   31914  0.0  0.3 17176748 107336 ?     Ss   Mar01 102:02 ora_arc1_bolan
oracle   31918  0.0  0.6 17279920 220532 ?     Ss   Mar01  24:13 ora_arc2_bolan
oracle   31922  0.0  0.7 17307772 243192 ?     Ss   Mar01 122:44 ora_arc3_bolan