Python中池中的Redis默认连接数

Question

Python-3.7版

Redis-2.10.6版

---

我正在为Redis创建一个连接池

redis_pool = redis.ConnectionPool(host=REDIS_URL, port=REDIS_PORT, decode_responses=True) 

我没有指定max_connections。在查看redis.ConnectionPool()的源代码时

def __init__(self, connection_class=Connection, max_connections=None,
             **connection_kwargs):
    """
    Create a connection pool. If max_connections is set, then this
    object raises redis.ConnectionError when the pool's limit is reached.

    By default, TCP connections are created unless connection_class is
    specified. Use redis.UnixDomainSocketConnection for unix sockets.

    Any additional keyword arguments are passed to the constructor of
    connection_class.
    """
    max_connections = max_connections or 2 ** 31
    if not isinstance(max_connections, (int, long)) or max_connections < 0:
        raise ValueError('"max_connections" must be a positive integer')

    self.connection_class = connection_class
    self.connection_kwargs = connection_kwargs
    self.max_connections = max_connections

    self.reset()

我看到max_connections设置为2**31即2147483648（如果未设置）。我觉得很奇怪。你知道吗

Redis在池中维护的默认连接数是多少？最大值约为200万。所以，这意味着我们必须传递我们自己的实际价值。你知道吗

Answer 1

Redis端不存在这个池，这个类实际上只是Python端的self.connection_class实例的奇特集合。你知道吗

不过，我同意你的看法，99%以上的时候2**31这个数字是不必要的巨大。不过，不要认为这太令人担心，因为初始化池不会创建任何连接（或为它们保留空间）。max_connections只限制_available_connections数组，当需要连接时数组会增长，但池中没有可立即使用的空闲数组。你知道吗

这里有更多的ConnectionPool类和一些注释。你知道吗

https://github.com/andymccurdy/redis-py/blob/master/redis/connection.py#L967

def reset(self):
    self.pid = os.getpid()
    self._created_connections = 0
    self._available_connections = []  # <- starts empty
    self._in_use_connections = set()
    self._check_lock = threading.Lock()

https://github.com/andymccurdy/redis-py/blob/master/redis/connection.py#L983

def get_connection(self, command_name, *keys, **options):
    "Get a connection from the pool"
    self._checkpid()
    try:
        connection = self._available_connections.pop()
    except IndexError:
        connection = self.make_connection()  # <- make a new conn only if _available_connections is tapped
    self._in_use_connections.add(connection)
    try:
        # ensure this connection is connected to Redis
        connection.connect()
        # connections that the pool provides should be ready to send
        # a command. if not, the connection was either returned to the
        # pool before all data has been read or the socket has been
        # closed. either way, reconnect and verify everything is good.
        if not connection.is_ready_for_command():
            connection.disconnect()
            connection.connect()
            if not connection.is_ready_for_command():
                raise ConnectionError('Connection not ready')
    except:  # noqa: E722
        # release the connection back to the pool so that we don't leak it
        self.release(connection)
        raise

    return connection

https://github.com/andymccurdy/redis-py/blob/master/redis/connection.py#L1019

 def make_connection(self):
    "Create a new connection"
    if self._created_connections >= self.max_connections:  # <- where the bounding happens
        raise ConnectionError("Too many connections")
    self._created_connections += 1
    return self.connection_class(**self.connection_kwargs)

无论如何，我敢打赌，选择这个特定的值是为了将开发人员完全耗尽池的可能性降低到接近0。注意，连接对象是非常轻量级的，因此数千或数百万个连接对象的数组不太可能使应用程序停止运行。实际上，这并没有什么区别：大多数Redis调用返回得如此之快，以至于你很难意外地同时启动数百万个Redis调用。（如果你是故意这么做的，你可能知道的足够多，可以根据你的具体需要调整一切。；—）