psycopg2.pool.PoolError: connection pool exhausted

psycopg2.pool 数据库连接池用完的两种情况:

1. sql报错, 导致数据库的链接putconn失败, 没有将conn添加到数据连接池中
2. 真的有那么连接建立, 假设连接池有100个数据库连接, 同时有101个查询需要链接,这时候肯定是会报链接池用完的, 这时候加连接池数量跟数据库连接数就可以了
   问题1: 出现的原因, 查询报错, 添加conn回连接池失败
   
   源码:self._pool.append(conn) 将这个连接重新添加到pool中

    def _putconn(self, conn, key=None, close=False):
        """Put away a connection."""
        if self.closed:
            raise PoolError("connection pool is closed")

        if key is None:
            key = self._rused.get(id(conn))
            if key is None:
                raise PoolError("trying to put unkeyed connection")

        if len(self._pool) < self.minconn and not close:
            # Return the connection into a consistent state before putting
            # it back into the pool
            if not conn.closed:
                status = conn.info.transaction_status
                if status == _ext.TRANSACTION_STATUS_UNKNOWN:
                    # server connection lost
                    conn.close()
                elif status != _ext.TRANSACTION_STATUS_IDLE:
                    # connection in error or in transaction
                    conn.rollback()
                    self._pool.append(conn)
                else:
                    # regular idle connection
                    self._pool.append(conn)
            # If the connection is closed, we just discard it.
        else:
            conn.close()
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解决方案: 加个try … except … finally就OK