无论你是新上线的系统还是已经上线很久的系统。我们都可以很简单的对Memcached进行配置，但是配置之前我们需要注意如下问题：
1.memcached is only a caching mechanism. It shouldn't be used to store information that you cannot
otherwise afford to lose and then load from a different location.
2.There is no security built into the memcached protocol. At a minimum, make sure that the servers
running memcached are only accessible from inside your network, and that the network ports being
used are blocked (using a firewall or similar). If the information on the memcached servers that is
being stored is any sensitive, then encrypt the information before storing it in memcached.
3. memcached does not provide any sort of failover. Because there is no communication between
different memcached instances. If an instance fails, your application must capable of removing it from
the list, reloading the data and then writing data to another memcached instance.
4. Latency between the clients and the memcached can be a problem if you are using different physical
machines for these tasks. If you find that the latency is a problem, move the memcached instances to
be on the clients.
5. Key length is determined by the memcached server. The default maximum key size is 250 bytes.
6. Try to use at least two memcached instances, especially for multiple clients, to avoid having a single
point of failure. Ideally, create as many memcached nodes as possible. When adding and removing
memcached instances from a pool, the hashing and distribution of key/value pairs may be affected.
7.Use Namespace.The memcached cache is a very simple massive key/value storage system, and as such there is no
way of compartmentalizing data automatically into different sections. For example, if you are storing
tables could run into issues because the same ID might be valid in both tables.
Some interfaces provide an automated mechanism for creating namespaces when storing information
into the cache. In practice, these namespaces are merely a prefix before a given ID that is applied
every time a value is stored or retrieve from the cache.
You can implement the same basic principle by using keys that describe the object and the unique
identifier within the key that you supply when the object is stored. For example, when storing user data,
prefix the ID of the user with user: or user-.
Memcached distribution algorithms:
The memcached client interface supports a number of different distribution algorithms that are used in
multi-server configurations to determine which host should be used when setting or getting data from
a given memcached instance. When you get or set a value, a hash is constructed from the supplied
key and then used to select a host from the list of configured servers. Because the hashing mechanism
uses the supplied key as the basis for the hash, the same server is selected during both set and get
operations.
You can think of this process as follows. Given an array of servers (a, b, and c), the client uses a
hashing algorithm that returns an integer based on the key being stored or retrieved. The resulting
value is then used to select a server from the list of servers configured in the client. Most standard
client hashing within memcache clients uses a simple modulus calculation on the value against the
number of configured memcached servers. You can summarize the process in pseudocode as:
@memcservers = ['a.memc',