pymongo中的连接操作：Connection()与MongoClient()

Posted 2020-09-23

class MongoClient(pymongo.common.BaseObject)

   Connection to MongoDB.
 
   Method resolution order:
       MongoClient
       pymongo.common.BaseObject
       __builtin__.object

class Connection(pymongo.mongo_client.MongoClient)
   Connection to MongoDB.
 
   Method resolution order:
       Connection
       pymongo.mongo_client.MongoClient
       pymongo.common.BaseObject
       __builtin__.object

我们先看一下源代码，从这两个类的继承来看，connection是继承了MongoClient的，建议使用MongoClient而不是使用Connection。

（也就是说，MongoClient能够用法Connection都能够使用）

from pymongo import MongoClient
client = MongoClient(‘192.168.40.87‘, 27037)
db_name = ‘TCL_Useraction‘
db = client[db_name]
collection_useraction = db[‘useraction‘]

这里是通过字典的方式訪问数据库和集合，同一时候你也能够通过.（点号）的方式訪问

做实验时。发现Python用Connection()连接时。改动操作速度非常快。而用MongoClient()建立的连接，操作速度慢非常多。

from pymongo import MongoClient,Connection  
import time 
db = Connection(‘192.168.1.101‘, 27017).performance_test 
#client = MongoClient(‘192.168.1.101‘, 27017)
#db = client.performance_test 


db.drop_collection("updates") 
collection = db.updates 
collection.insert({"x": 1}) 
collection.find_one() 
start = time.time() 
for i in range(100000): 
        collection.update({}, {"$push" : {"x" : 1}}) 
...




>python test_mongo_conn.py
8.43799996376
>python test_mongo_client.py
62.5780000687

用Connection() 8秒，MongoClient()则花了62秒。这性能相差也太多了。
非常是疑惑，于是查了pymongo的文档，原来两者有个选项的默认行为不同：




class pymongo.connection.Connection([host=‘localhost‘[,port=27017[,max_pool_size=10[,network_timeout=None[, document_class=dict[, tz_aware=False[, **kwargs]]]]]]])


Write Concern options:

safe: Connection disables acknowledgement of write operations. Use safe=True to enable write acknowledgement.

w: (integer or string) If this is a replica set, write operations will block until they have been replicated to the specified number or tagged set of servers. w=<int> always includes the replica set primary (e.g. w=3 means write to the primary and wait until replicated to two secondaries). Implies safe=True.

wtimeout: (integer) Used in conjunction with w. Specify a value in milliseconds to control how long to wait for write propagation to complete. If replication does not complete in the given timeframe, a timeout exception is raised. Implies safe=True.

j: If True block until write operations have been committed to the journal. Ignored if the server is running without journaling. Implies safe=True.

fsync: If True force the database to fsync all files before returning. When used with j the server awaits the next group commit before returning. Implies safe=True.




safe选项决定操作是“瞬时完毕”与“安全操作”。connection()默认是safe=False,即瞬时完毕，不等server回应，而MongoClient()默认是safe=True。即安全操作，等server确认后才继续下一步操作。
所以一个8秒，一个62秒，这个差距实际上是“瞬时完毕”与“安全操作”两者的性能区别。

当将Connection() 和MongoClient()建立连接时指定同样的safe參数，两者的性能表现是一样的。

client = MongoClient(‘192.168.1.101‘, 27017,safe=False)
#db = Connection(‘192.168.1.101‘, 27017,safe=False).performance_test