ORA-00020错误是由于进程数设置过低，导致进程数用完，数据库无法连接不上，从而爆出ora-00020错误。

11g 11.2.0.4版本

用户系统需要的进程数，上线前一次性设置完毕！

SYS@orcl>show parameter process;

NAME TYPE VALUE

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

aq_tm_processes integer 1

cell_offload_processing boolean TRUE

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 8

processes integer 40

processor_group_name string

SYS@orcl>select count(*) from v$process;

COUNT(*)

----------

34

最大可用进程数40-34=6个其实可用只有5个

11.2.0.4中发现processes最少不能少于40个 process进程数至少有32个以上设置processes少于40个将默认设置为40

实验中我设置processes=10，最后显示结果

SYS@orcl>alter system set processes=10 scope=spfile;

System altered.

SYS@orcl>shutdown immediate;

Database closed.

Database dismounted.

ORACLE instance shut down.

SYS@orcl>startup ;

ORACLE instance started.

Total System Global Area 1503199232 bytes

Fixed Size 2253424 bytes

Variable Size 905973136 bytes

Database Buffers 587202560 bytes

Redo Buffers 7770112 bytes

Database mounted.

Database opened.

SYS@orcl>show parameter processes;