如何检查 MongoDB 实例的客户端是否有效？

问题描述 投票：0回答：8

特别是，我目前正在尝试使用以下函数检查与客户端的连接是否有效：

def mongodb_connect(client_uri):
    try:
        return pymongo.MongoClient(client_uri)
    except pymongo.errors.ConnectionFailure:
         print "Failed to connect to server {}".format(client_uri)

然后我像这样使用这个函数：

def bucket_summary(self):
    client_uri = "some_client_uri"
    client = mongodb_connect(client_uri)
    db = client[tenant_id]
    ttb = db.timebucket.count() # If I use an invalid URI it hangs here

如果给出了无效的 URI，有没有办法在最后一行捕获并抛出异常？我最初认为这就是 ConnectionFailure 的用途（因此连接时可能会捕获），但我错了。

如果我使用无效的 URI 运行程序，该程序无法运行，则发出 KeyboardInterrupt 会产生：

File "reportjob_status.py", line 58, in <module>
tester.summarize_timebuckets()
File "reportjob_status.py", line 43, in summarize_timebuckets
ttb = db.timebucket.count() #error
File "/Library/Python/2.7/site-packages/pymongo/collection.py", line   1023, in count
return self._count(cmd)
File "/Library/Python/2.7/site-packages/pymongo/collection.py", line 985, in _count
with self._socket_for_reads() as (sock_info, slave_ok):
File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/contextlib.py", line 17, in __enter__
return self.gen.next()
File "/Library/Python/2.7/site-packages/pymongo/mongo_client.py", line 699, in _socket_for_reads
with self._get_socket(read_preference) as sock_info:
File  "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/contextlib.py", line 17, in __enter__
return self.gen.next()
File "/Library/Python/2.7/site-packages/pymongo/mongo_client.py", line 663, in _get_socket
server = self._get_topology().select_server(selector)
File "/Library/Python/2.7/site-packages/pymongo/topology.py", line 121, in select_server
address))
File "/Library/Python/2.7/site-packages/pymongo/topology.py", line 106, in select_servers
self._condition.wait(common.MIN_HEARTBEAT_INTERVAL)
File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py", line 358, in wait
_sleep(delay)
python mongodb pymongo
8个回答
90
投票

serverSelectionTimeoutMS
的
pymongo.mongo_client.MongoClient关键字参数控制驱动程序尝试连接到服务器的时间长度。默认值为 30 秒。



将其设置为与您的典型连接时间兼容的非常低的值1以立即报告错误。之后您需要查询数据库以触发连接尝试：



>>> maxSevSelDelay = 1 # Assume 1ms maximum server selection delay
>>> client = pymongo.MongoClient("someInvalidURIOrNonExistantHost",
                                 serverSelectionTimeoutMS=maxSevSelDelay)
//                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>> client.server_info()




这会提高
pymongo.errors.ServerSelectionTimeoutError
。



¹ 显然将
serverSelectionTimeoutMS
设置为
0
甚至可能在您的服务器具有非常低延迟的特定情况下工作（例如负载非常轻的“本地”服务器的情况）






由您来捕获该异常并正确处理它。类似的东西：


try:
    client = pymongo.MongoClient("someInvalidURIOrNonExistantHost",
                                     serverSelectionTimeoutMS=maxSevSelDelay)
    client.server_info() # force connection on a request as the
                         # connect=True parameter of MongoClient seems
                         # to be useless here 
except pymongo.errors.ServerSelectionTimeoutError as err:
    # do whatever you need
    print(err)



将显示：



No servers found yet

    



      

      
      
      

      

        

          

            

              
27
投票

              
            

          

        

        
您好，要了解连接是否已建立，您可以这样做：



from pymongo import MongoClient
from pymongo.errors import ConnectionFailure
client = MongoClient()
try:
   # The ismaster command is cheap and does not require auth.
   client.admin.command('ismaster')
except ConnectionFailure:
   print("Server not available")

    



      

      
      
      

      

        

          

            

              
4
投票

              
            

          

        

        
服务器选择超时MS



  
这定义了在抛出异常之前阻止服务器选择的时间
  例外。默认值为 30,000（毫秒）。一定是
  可在客户端级别进行配置。它不能在
  数据库对象、集合对象的级别或
  个别查询。

  
  
选择此默认值足以满足典型服务器的需要
  初选完成。随着服务器速度的提高
  选举，这个数字可能会向下修改。

  
  
能够容忍服务器选择时较长延迟的用户
  拓扑不断变化可以将其设置得更高。想要“失败”的用户
  fast”，当拓扑处于变化状态时，可以将其设置为一个较小的数字。

  
  
serverSelectionTimeoutMS 为零可能在某些情况下具有特殊含义
  司机；本规范中未定义零的含义，但所有驱动程序
  应记录零的含义。





https://github.com/mongodb/specifications/blob/master/source/server-selection/server-selection.rst#serverselectiontimeoutms


# pymongo 3.5.1
from pymongo import MongoClient
from pymongo.errors import ServerSelectionTimeoutError

client = MongoClient("mongodb://localhost:27000/", serverSelectionTimeoutMS=10, connectTimeoutMS=20000)

try:
    info = client.server_info() # Forces a call.
except ServerSelectionTimeoutError:
    print("server is down.")

# If connection create a new one with serverSelectionTimeoutMS=30000

    



      

      
      
      

      

        

          

            

              
2
投票

              
            

          

        

        
serverSelectionTimeoutMS
 对我不起作用（Python 2.7.12、MongoDB 3.6.1、pymongo 3.6.0）。 
A. Jesse Jiryu Davis在GitHub问题中建议我们首先尝试套接字级连接作为试金石。这对我有用。


def throw_if_mongodb_is_unavailable(host, port):
    import socket
    sock = None
    try:
        sock = socket.create_connection(
            (host, port),
            timeout=1) # one second
    except socket.error as err:
        raise EnvironmentError(
            "Can't connect to MongoDB at {host}:{port} because: {err}"
            .format(**locals()))
    finally:
        if sock is not None:
            sock.close()

# elsewhere...
HOST = 'localhost'
PORT = 27017
throw_if_mongodb_is_unavailable(HOST, PORT)
import pymongo
conn = pymongo.MongoClient(HOST, PORT)
print(conn.admin.command('ismaster'))
# etc.



有很多问题无法捕获，但如果服务器未运行或无法访问，它会立即向您显示。

    



      

      
      
      

      

        

          

            

              
0
投票

              
            

          

        

        
也可以这样检查：


from pymongo import MongoClient
from pymongo.errors import OperationFailure

def check_mongo_connection(client_uri):
    connection = MongoClient(client_uri)

    try:
        connection.database_names()
        print('Data Base Connection Established........')

    except OperationFailure as err:
        print(f"Data Base Connection failed. Error: {err}")

check_mongo_connection(client_uri)

    



      

      
      
      

      

        

          

            

              
0
投票

              
            

          

        

        
对于 
pymongo >= 4.0 首选方法是使用 ping
 命令 
而不是已弃用的 ismaster
:

from pymongo.errors import ConnectionFailure
client = MongoClient()

try:
    client.admin.command('ping')
except ConnectionFailure:
    print("Server not available")

要处理身份验证失败，请包含 
OperationFailure
:


except OperationFailure as err:
    print(f"Database error encountered: {err}")

来源：
mongo_client.py
    



      

      
      
      

      

        

          

            

              
0
投票

              
            

          

        

        
def mongo_available():
    maxsevseldelay = 1  # Assume 1ms maximum server selection delay
    client = pymongo.MongoClient('mongodb://localhost:27017,localhost2:27017',serverSelectionTimeoutMS=maxsevseldelay)
    try:
        # The ping command is cheap and does not require auth.
        client.admin.command('ping')
        return True, "Mongo connection working fine"
    except ConnectionFailure:
        return False, "Mongo Server not available"
        

mongo_available()
(False, 'Mongo Server not available')

    



      

      
      
      

      

        

          

            

              
0
投票

              
            

          

        

        
这将循环 30 秒，尝试 ping 到您的部署。对我来说效果很好。


# Connect to Mongo client
client = MongoClient(mongo_connection_string)

# Send a ping to confirm a successful connection
end_time = time.time() + 30
while time.time() < end_time:
    try:
        client.admin.command('ping')
        print("Pinged your deployment. You successfully connected to MongoDB!")
        break  # Successful connection, exit the loop
    except Exception as e:
        print(f"Failed to connect: {e}")

    



      

      
    

  

  

    
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