中文异常提示为：ORA-00020 超出最大进程数(s%)
英文异常提示为：ORA-00020 maximum number of processes num exceeded
出现该异常的时候，可按如下步骤检查数据库：
（1）首先检查进程设置，看看是否由于允许进程数设置过低造成：
SQL> show parameter process;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
aq_tm_processes integer 0
db_writer_processes integer 4
job_queue_processes integer 10
log_archive_max_processes integer 2
processes integer 3000
（2）如果进程数足够，那么很可能是应用未释放连接造成：
select * from v$session
检查未释放的连接，将其结束掉。
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Cause:
An operation requested a resource that was unavailable. The maximum number of processes is specified by the initialization parameter PROCESSES. When this maximum is reached, no more requests are processed.
Action:
Try the operation again in a few minutes. If this message occurs often, shut down Oracle, increase the PROCESSES parameter in the initialization parameter file, and restart Oracle.