Oracle sessions,processes 和 transactions 参数 关系 说明
1.Oracle官方文档11gR2说明
1.1 processes
PROCESSES
|
Property |
Description |
|
Parameter type |
Integer |
|
Default value |
100 |
|
Modifiable |
No |
|
Range of values |
6 to operating system dependent |
|
Basic |
Yes |
|
Oracle RAC |
Multiple instances can have different values. |
PROCESSES specifies the maximum number of operating system user processes that can simultaneously connect to Oracle. Its value should allow for all background processes such as locks, job queue processes, and parallel execution processes.
The default values of the SESSIONS and TRANSACTIONS parameters are derived from this parameter. Therefore, if you change the value of PROCESSES, you should evaluate whether to adjust the values of those derived parameters.（如果修改processes参数，应该考虑修改sessions和transactions参数）
reference http://docs.oracle.com/cd/E11882_01/server.112/e40402/initparams202.htm#REFRN10175
1.2 sessions
SESSIONS
|
Property |
Description |
|
Parameter type |
Integer |
|
Default value |
Derived: (1.5 * PROCESSES) + 22 |
|
Modifiable |
No |
|
Range of values |
1 to 216 (which is 1 to 65536) |
|
Basic |
Yes |
这里要注意的是到了11gR2里，sessions 的默认值计算方式变了。 该值的计算是针对dedicate 模式的。
SESSIONS specifies the maximum number of sessions that can be created in the system. Because every login requires a session, this parameter effectively determines the maximum number of concurrent users in the system. You should always set this parameter explicitly to a value equivalent to your estimate of the maximum number of concurrent users, plus the number of background processes, plus approximately 10% for recursive sessions.
Oracle uses the default value of this parameter as its minimum. Values between 1 and the default do not trigger errors, but Oracle ignores them and uses the default instead.
The default values of the ENQUEUE_RESOURCES and TRANSACTIONS parameters are derived from SESSIONS. Therefore, if you increase the value of SESSIONS, you should consider whether to adjust the values of ENQUEUE_RESOURCES and TRANSACTIONS as well. (Note that ENQUEUE_RESOURCES is obsolete as of Oracle Database 10g release 2 (10.2).)
In a shared server environment, the value of PROCESSES can be quite small. Therefore, Oracle recommends that you adjust the value of SESSIONS to approximately 1.1 * total number of connections.
reference http://docs.oracle.com/cd/E11882_01/server.112/e40402/initparams234.htm#REFRN10197
1.3 transactions
TRANSACTIONS
|
Property |
Description |
|
Parameter type |
Integer |
|
Default value |
Derived: (1.1 * SESSIONS) |
|
Modifiable |
No |
|
Range of values |
4 to 232 |
|
Oracle RAC |
Multiple instances can have different values. |
TRANSACTIONS specifies how many rollback segments to online when UNDO_MANAGEMENT = MANUAL. The maximum number of concurrent transactions is now restricted by undo tablespace size (UNDO_MANAGEMENT = AUTO) or the number of online rollback segments (UNDO_MANAGEMENT = MANUAL).
reference http://docs.oracle.com/cd/E11882_01/server.112/e40402/initparams262.htm#REFRN10222
2.修改参数实验
2.1 当前数据库版本
sys@ORCL>select * from v$version;
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
PL/SQL Release 11.2.0.4.0 - Production
CORE 11.2.0.4.0 Production
TNS for Linux: Version 11.2.0.4.0 - Production
NLSRTL Version 11.2.0.4.0 - Production
2.2 当前环境默认参数
sys@ORCL>show parameter processes
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
processes integer 150
sys@ORCL>show parameter sessions
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
sessions integer 248
----按照11gR2中的计算方法：SESSIONS=(1.5*PROCESSES) +22 =(1.5*150) +22=247
sys@ORCL>show parameter transactions
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
transactions integer 272
----按照11gR2中的计算方法：TRANSACTIONS =(1.1*SESSIONS) =(1.1*248) =272.8
2.3 只增加processes到1000，观察sessions和transactions参数
sys@ORCL>create pfile='/home/oracle/pfile.bak' from spfile;
File created.
sys@ORCL>alter system set processes=1000 scope=spfile;
System altered.
sys@ORCL>startup force
ORACLE instance started.
Total System Global Area 768294912 bytes
Fixed Size 2257192 bytes
Variable Size 633343704 bytes
Database Buffers 125829120 bytes
Redo Buffers 6864896 bytes
Database mounted.
Database opened.
sys@ORCL>show parameter processes
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
processes integer 1000
sys@ORCL>show parameter sessions
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
sessions integer 1522
sys@ORCL>show parameter transaction
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
transactions integer 1674
当我们修改processes 之后，如果sessions 和transactions 小于由公式计算出来的值，就会自动进行修改。为了验证这个观点，我们在做一个测试，修改processes 值，同时修改sessions和transactions的值，使其大于公式计算出来的值。
2.4 同时修改processes，sessions，transaction值
修改processes=300
根据公式：sessions=1.5*processes +22=1.5*300+22=472
transactions=1.1*sessions=1.1*472=519.2
此时，我们设置sessions=800，transactions=1000
sys@ORCL>alter system set processes=300 scope=spfile;
System altered.
sys@ORCL>alter system set sessions=800 scope=spfile;
System altered.
sys@ORCL>alter system set transactions=1000 scope=spfile;
System altered.
sys@ORCL>startup force
ORACLE instance started.
Total System Global Area 768294912 bytes
Fixed Size 2257192 bytes
Variable Size 427822808 bytes
Database Buffers 331350016 bytes
Redo Buffers 6864896 bytes
Database mounted.
Database opened.
sys@ORCL>show parameter processes
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
processes integer 300
sys@ORCL>show parameter sessions
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
sessions integer 800
sys@ORCL>show parameter transactions
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
transactions integer 1000
----还原：
sys@ORCL>shut abort
sys@ORCL>create spfile from pfile='/home/oracle/pfile.bak';
sys@ORCL>startup
sys@ORCL>show parameter processes
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
processes integer 150
sys@ORCL>show parameter sessions
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
sessions integer 248
sys@ORCL>show parameter transactions
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
transactions integer 272
reference http://www.2cto.com/database/201110/108586.html
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