关于Redis的Python客户端的连接池问题

 

在一次分享中提到了Redis的长短链接的问题，引发了对redis-py的连接池机制的讨论。

 

 

通过源码发现，每创建一个Redis实例都会构造出一个ConnectionPool，每一次访问redis都会从这个连接池得到一个连接，访问完成之后，会把该连接放回连接池，下面是发送命令访问redis的execute_command方法实现：

 

 

 352     #### COMMAND EXECUTION AND PROTOCOL PARSING ####

 353     def execute_command(self, *args, **options):

 354         "Execute a command and return a parsed response"

 355         pool = self.connection_pool

 356         command_name = args[0]

 357         connection = pool.get_connection(command_name, **options)

 358         try:

 359             connection.send_command(*args)

 360             return self.parse_response(connection, command_name, **options)

 361         except ConnectionError:

 362             connection.disconnect()

 363             connection.send_command(*args)

 364             return self.parse_response(connection, command_name, **options)

 365         finally:

 366             pool.release(connection)

 

当然，也可以构造一个ConnectionPool，在创建Redis实例时，可以将该ConnectionPool传入，那么后续的操作会从给定的ConnectionPool获得连接。

 

redis-py的作者在文档中也有详细说明：

 

Connection Pools

Behind the scenes, redis-py uses a connection pool to manage connections to a Redis server. By default, each Redis instance you create will in turn create its own connection pool. You can override this behavior and use an existing connection pool by passing an already created connection pool instance to the connection_pool argument of the Redis class. You may choose to do this in order to implement client side sharding or have finer grain control of how connections are managed.

>>> pool = redis.ConnectionPool(host='localhost', port=6379, db=0)

>>> r = redis.Redis(connection_pool=pool)

 

 

关于redis-server的最大客户端数量问题

 

redis的文档这样说：

 

# Set the max number of connected clients at the same time. By default there

# is no limit, and it's up to the number of file descriptors the Redis process

# is able to open. The special value '0' means no limits.

# Once the limit is reached Redis will close all the new connections sending

# an error 'max number of clients reached'.

#

# maxclients 128

 

1） redis默认没有设置最大的连接客户端数量，这个数量取决于redis进程能够打开的文件句柄数量。

 

2） 可以手工配置最大的连接池数量。