Oracle sessions,processes 和 transactions 参数 关系 说明

一.官网说明

1.1 processes

11gR2 的文档：

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.

PROCESSESspecifies the maximum numberof operating system user processes that can simultaneously connect to Oracle.Its value should allow for all background processes such as locks, job queueprocesses, and parallel execution processes.

The defaultvalues of theSESSIONSandTRANSACTIONSparameters arederived from this parameter. Therefore, if you change the valueofPROCESSES, you should evaluate whether to adjust the values of thosederived parameters.

http://download.oracle.com/docs/cd/E11882_01/server.112/e25513/initparams198.htm#REFRN10175

1.2 sessions

11gR1:

http://download.oracle.com/docs/cd/B28359_01/server.111/b28320/initparams220.htm#REFRN10197

Property	Description
Parameter type	Integer
Default value	Derived: (1.1 *PROCESSES) + 5
Modifiable	No
Range of values	1 to 231
Basic	Yes

11gR2

Property	Description
Parameter type	Integer
Default value	Derived: (1.5 *PROCESSES) + 22
Modifiable	No
Range of values	1 to 231
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。

SESSIONSspecifies the maximum number of sessions that can becreated in the system. Because every login requires a session, this parametereffectively determines the maximum number of concurrent users in the system.You should always set this parameter explicitly to a value equivalent to yourestimate of the maximum number of concurrent users, plus the number ofbackground processes, plus approximately 10% for recursive sessions.

Oracle uses thedefault value of this parameter as its minimum. Values between 1 and thedefault do not trigger errors, but Oracle ignores them and uses the defaultinstead.

The defaultvalues of theENQUEUE_RESOURCESandTRANSACTIONSparametersare derived fromSESSIONS. Therefore, if you increase the valueofSESSIONS, you should consider whether to adjust the valuesofENQUEUE_RESOURCESandTRANSACTIONSas well. (NotethatENQUEUE_RESOURCESis obsolete as of Oracle Database 10g release2 (10.2).)

In a shared server environment, the value ofPROCESSEScanbe quite small. Therefore, Oracle recommends that youadjust the value ofSESSIONSto approximately 1.1 * total numberofconnections.

1.3 transactions

11gR2

http://download.oracle.com/docs/cd/E11882_01/server.112/e25513/initparams258.htm#REFRN10222

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.

TRANSACTIONSspecifieshow many rollback segments to onlinewhenUNDO_MANAGEMENT=MANUAL. The maximum number of concurrenttransactions is now restricted by undo tablespace size(UNDO_MANAGEMENT=AUTO) or the number of online rollback segments(UNDO_MANAGEMENT=MANUAL).

二. 测试

2.1 测试DB版本

SQL> select * from v$version;

BANNER

-----------------------------------------------------------------------

Oracle Database 11g Enterprise EditionRelease 11.2.0.1.0 - Production

PL/SQL Release 11.2.0.1.0 - Production

CORE11.2.0.1.0 Production

TNS for 32-bit Windows: Version 11.2.0.1.0- Production

NLSRTL Version 11.2.0.1.0 - Production

SQL> show parameter processes

NAME TYPE VALUE

----------------------------------------------- -----------

aq_tm_processes integer 0

db_writer_processes integer 1

gcs_server_processes integer 0

global_txn_processes integer 1

job_queue_processes integer 1000

log_archive_max_processes integer 4

processes integer 150

SQL> show parameter sessions

NAME TYPE VALUE

----------------------------------------------- -----------

java_max_sessionspace_size integer 0

java_soft_sessionspace_limit integer 0

license_max_sessions integer 0

license_sessions_warning integer 0

sessions integer 248

shared_server_sessions integer

按照11gR2的中的计算方法：SESSIONS=(1.5*PROCESSES) + 22

SESSIONS=1.5*150+22=247

SQL> show parameter transaction

NAME TYPE VALUE

----------------------------------------------- -------

transactions integer272

transactions_per_rollback_segment integer5

根据公式：transaction= (1.1 *SESSIONS)

1.1*248==272.8

2.2 只增加processes到1000，观察sessions 和 transactions 参数

SQL> create pfile from spfile;

File created.

然后修改init 文件，将processes 修改成1000。

SQL> shutdown immediate

Database closed.

Database dismounted.

ORACLE instance shut down.

SQL> create spfile frompfile='D:\app\Administrator\product\11.2.0\dbhome_1\database\INITnewccs.ORA';

File created.

SQL> startup

ORACLE instance started.

Total System Global Area 1071333376 bytes

Fixed Size 1375792 bytes

Variable Size 595591632 bytes

Database Buffers 469762048 bytes

Redo Buffers 4603904 bytes

Database mounted.

Database opened.

SQL> show parameter processes

NAME TYPE VALUE

----------------------------------------------- ------------------

aq_tm_processes integer 0

db_writer_processes integer 1

gcs_server_processes integer 0

global_txn_processes integer 1

job_queue_processes integer 1000

log_archive_max_processes integer 4

processes integer 1000

SQL> show parameter sessions

NAME TYPE VALUE

----------------------------------------------- ------------------

java_max_sessionspace_size integer 0

java_soft_sessionspace_limit integer 0

license_max_sessions integer 0

license_sessions_warning integer 0

sessions integer 1522

shared_server_sessions integer

SQL> show parameter transaction

NAME TYPE VALUE

----------------------------------------------- ------------------

transactions integer 1674

transactions_per_rollback_segment integer5

SQL>

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。

2.3 同时修改processes，sessions和transactions 值

Processes 设为500

根据公式：sessions=1.5*500+22=772

Transactions=1.1*sessions=850

我们将sessions 设置为900，transactions 设置为1000

*.processes=500

*.sessions=900

*.transactions=1000

SQL> shutdown immediate

Database closed.

Database dismounted.

ORACLE instance shut down.

SQL> create spfile frompfile='D:\app\Administrator\product\11.2.0\dbhome_1\database\INITnewccs.ORA';

File created.

SQL> startup

ORACLE instance started.

Total System Global Area 1071333376 bytes

Fixed Size 1375792 bytes

Variable Size 595591632 bytes

Database Buffers 469762048 bytes

Redo Buffers 4603904 bytes

Database mounted.

Database opened.

SQL>

SQL>show parameter processes

NAME TYPE VALUE

----------------------------------------------- ------------------------------

aq_tm_processes integer 0

db_writer_processes integer 1

gcs_server_processes integer 0

global_txn_processes integer 1

job_queue_processes integer 1000

log_archive_max_processes integer 4

processes integer 500

SQL> show parameter sessions

NAME TYPE VALUE

----------------------------------------------- ------------------------------

java_max_sessionspace_size integer 0

java_soft_sessionspace_limit integer 0

license_max_sessions integer 0

license_sessions_warning integer 0

sessions integer 900

shared_server_sessions integer

SQL> show parameter transactions

NAME TYPE VALUE

----------------------------------------------- ------------------------------

transactions integer 1000

transactions_per_rollback_segment integer5

SQL>

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