最近监控系统的数据库监控总是延迟，查看日志报错：
2015-08-27 10:20:19,534 ERROR Traceback (most recent call last):
File "oracle_mon.py", line 306, in
update_status(ip, 'stop', timer.end_date) File "oracle_mon.py", line 285, in update_status pg.db.update("oracle_mon", where=where, status=status, stat_date=status_date) File "/usr/lib/python2.7/site-packages/web/db.py", line 881, in update db_cursor = self._db_cursor() File "/usr/lib/python2.7/site-packages/web/db.py", line 566, in _db_cursor return self.ctx.db.cursor() File "/usr/lib/python2.7/site-packages/web/db.py", line 507, in _getctx self._load_context(self._ctx) File "/usr/lib/python2.7/site-packages/web/db.py", line 516, in _load_context ctx.db = self._connect_with_pooling(self.keywords) File "/usr/lib/python2.7/site-packages/web/db.py", line 970, in _connect_with_pooling conn = DB._connect_with_pooling(self, keywords) File "/usr/lib/python2.7/site-packages/web/db.py", line 563, in _connect_with_pooling return self._pooleddb.connection() File "/usr/lib/python2.7/site-packages/DBUtils-1.1-py2.7.egg/DBUtils/PooledDB.py", line 331, in connection con = self.steady_connection() File "/usr/lib/python2.7/site-packages/DBUtils-1.1-py2.7.egg/DBUtils/PooledDB.py", line 279, in steady_connection *self._args, **self._kwargs) File "/usr/lib/python2.7/site-packages/DBUtils-1.1-py2.7.egg/DBUtils/SteadyDB.py", line 134, in connect failures, ping, closeable, *args, **kwargs) File "/usr/lib/python2.7/site-packages/DBUtils-1.1-py2.7.egg/DBUtils/SteadyDB.py", line 186, in __init__ self._store(self._create()) File "/usr/lib/python2.7/site-packages/DBUtils-1.1-py2.7.egg/DBUtils/SteadyDB.py", line 190, in _create con = self._creator(*self._args, **self._kwargs) File "/usr/lib64/python2.7/site-packages/psycopg2/__init__.py", line 179, in connect connection_factory=connection_factory, async=async) OperationalError: 致命错误: 已保留的连接位置为执行非复制请求的超级用户预留
查到数据库使用的活动连接数为90左右，而pg的默认最大连接数MAX_CONNECTION=100，怀疑是数据库连接数过多导致报错。
事实果然如此，老数据库的MAX_CONNECTION=200，并没有使用默认的100。
解决办法：修改配置文件（postgresql.conf）中的默认最大连接数MAX_CONNECTION=200，重启数据库即可。