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. |
PROCESSES specifies 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 the SESSIONS and TRANSACTIONS parameters arederived from this parameter. Therefore, if you change the valueof PROCESSES, 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
http://download.oracle.com/docs/cd/B28359_01/server.111/b28320/initparams220.htm#REFRN10197
Property | Description |
Parameter type | Integer |
Default value | Derived: (1.1 * |
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。
SESSIONS specifies 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 the ENQUEUE_RESOURCES and TRANSACTIONS parametersare derived from SESSIONS. Therefore, if you increase the valueof SESSIONS, you should consider whether to adjust the valuesof ENQUEUE_RESOURCES and TRANSACTIONS as well. (Notethat ENQUEUE_RESOURCES is obsolete as of Oracle Database 10g release2 (10.2).)
In a shared server environment, the value of PROCESSES canbe quite small. Therefore, Oracle recommends that youadjust the value of SESSIONS to approximately 1.1 * total numberof connections.
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. |
TRANSACTIONS specifieshow many rollback segments to onlinewhen UNDO_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
CORE 11.2.0.1.0 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 integer 272
transactions_per_rollback_segment integer 5
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 integer 5
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 integer 5
SQL>
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