large pool太小导致shared server异常

数据库出现如下错误

Fri Oct  5 09:33:54 2012
Process S001 started up but failed with error = 20
failed to start shared server 'S001', oer=20
Process S001 started up but failed with error = 20
failed to start shared server 'S001', oer=20
Process S001 started up but failed with error = 20
failed to start shared server 'S001', oer=20
Process S001 started up but failed with error = 20
failed to start shared server 'S001', oer=20
Process S001 started up but failed with error = 20
failed to start shared server 'S001', oer=20
Process S001 started up but failed with error = 20
failed to start shared server 'S001', oer=20
Process S001 started up but failed with error = 20
failed to start shared server 'S001', oer=20
Process S001 started up but failed with error = 20
failed to start shared server 'S001', oer=20

重启后错误提示变为

Successfully onlined Undo Tablespace 1.
Fri Oct  5 09:34:41 2012
SMON: enabling tx recovery
Fri Oct  5 09:34:41 2012
Database Characterset is AL32UTF8
replication_dependency_tracking turned off (no async multimaster replication found)
Completed: ALTER DATABASE OPEN
Fri Oct  5 13:53:50 2012
Errors in file /oracle/admin/ora/bdump/ora_s000_25948.trc:
ORA-04031: unable to allocate 72 bytes of shared memory 
("large pool","unknown object","session heap","trigger condition node")
Fri Oct  5 13:53:50 2012
Errors in file /oracle/admin/ora/bdump/ora_s000_25948.trc:
ORA-00600: internal error code, arguments: [ksudel1], [], [], [], [], [], [], []
ORA-04031: unable to allocate 72 bytes of shared memory 
("large pool","unknown object","session heap","trigger condition node")
Fri Oct  5 13:54:52 2012
found dead shared server 'S000', pid = (11, 1)
Fri Oct  5 17:25:59 2012
Errors in file /oracle/admin/ora/bdump/ora_s000_31081.trc:
ORA-04031: unable to allocate 72 bytes of shared memory 
("large pool","unknown object","session heap","trigger condition node")
Fri Oct  5 17:25:59 2012
Errors in file /oracle/admin/ora/bdump/ora_s000_31081.trc:
ORA-00600: internal error code, arguments: [ksudel1], [], [], [], [], [], [], []
ORA-04031: unable to allocate 72 bytes of shared memory 
("large pool","unknown object","session heap","trigger condition node")

通过这里的错误,我们可以看到是large pool不能分配72 bytes的连续内存空间而使得S000进程报错.那这两者有什么联系:我们知道S000是shared server的进程,那shared server为什么导致large pool不足呢？查询官方文档得出,如下三种情况会使用large pool

Session memory for the shared server and the Oracle XA interface 
(used where transactions interact with more than one database)

I/O server processes

Oracle backup and restore operations

主要也就是shared server/parallel query buffers/backup restore这几个操作会使用到large pool.在该案例中很明显的可以看到是因为shared server进程需要分配large pool中一部分空间,而没有连续空间从而出现该错误.数据库相关参数配置

SQL> show parameter mts;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
mts_circuits                         integer     555
mts_dispatchers                      string      (PROTOCOL=TCP) (SERVICE=oraXDB)
mts_listener_address                 string
mts_max_dispatchers                  integer     5
mts_max_servers                      integer     20
mts_multiple_listeners               boolean     FALSE
mts_servers                          integer     1
mts_service                          string      ora
mts_sessions                         integer     550

SQL> show parameter large;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
large_pool_size                      big integer 16777216

这里可以看出来,数据库明显配置了MTS,因为数据库在启动时候,最少会建立一个shared server进程,而这个时候因为large pool太小(16M),导致该进程无法正常建立,从而出现上述alert中相关错误,临时处理方法增加large pool.后续需要关注业务特点,考虑是否可以采用Oracle Dedicated server模式来处理.