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Getting started!
================
A comprehensive, fast, pure-Python memcached client library.
Basic Usage
------------
.. code-block:: python
from pymemcache.client.base import Client
client = Client(('localhost', 11211))
client.set('some_key', 'some_value')
result = client.get('some_key')
Using UNIX domain sockets
-------------------------
You can also connect to a local memcached server over a UNIX domain socket by
passing the socket's path to the client's ``server`` parameter:
.. code-block:: python
from pymemcache.client.base import Client
client = Client('/var/run/memcached/memcached.sock')
Using a memcached cluster
-------------------------
This will use a consistent hashing algorithm to choose which server to
set/get the values from. It will also automatically rebalance depending
on if a server goes down.
.. code-block:: python
from pymemcache.client.hash import HashClient
client = HashClient([
('127.0.0.1', 11211),
('127.0.0.1', 11212)
])
client.set('some_key', 'some value')
result = client.get('some_key')
Serialization
--------------
.. code-block:: python
import json
from pymemcache.client.base import Client
def json_serializer(key, value):
if type(value) == str:
return value, 1
return json.dumps(value), 2
def json_deserializer(key, value, flags):
if flags == 1:
return value
if flags == 2:
return json.loads(value)
raise Exception("Unknown serialization format")
client = Client(('localhost', 11211), serializer=json_serializer,
deserializer=json_deserializer)
client.set('key', {'a':'b', 'c':'d'})
result = client.get('key')
pymemcache provides a default
`pickle <https://docs.python.org/3/library/pickle.html>`_-based serializer:
.. code-block:: python
from pymemcache.client.base import Client
from pymemcache import serde
class Foo(object):
pass
client = Client(('localhost', 11211),
serializer=serde.python_memcache_serializer,
deserializer=serde.python_memcache_deserializer)
client.set('key', Foo())
result client.get('key')
The serializer uses the highest pickle protocol available. In order to make
sure multiple versions of Python can read the protocol version, you can specify
the version with :code:`get_python_memcache_serializer`
.. code-block:: python
client = Client(('localhost', 11211),
serializer=serde.get_python_memcache_serializer(pickle_version=2),
deserializer=serde.python_memcache_deserializer)
Deserialization with python3
----------------------------
.. code-block:: python
def json_deserializer(key, value, flags):
if flags == 1:
return value.decode('utf-8')
if flags == 2:
return json.loads(value.decode('utf-8'))
raise Exception("Unknown serialization format")
Key Constraints
---------------
This client implements the ASCII protocol of memcached. This means keys should not
contain any of the following illegal characters:
> Keys cannot have spaces, new lines, carriage returns, or null characters.
We suggest that if you have unicode characters, or long keys, you use an effective
hashing mechanism before calling this client. At Pinterest, we have found that
murmur3 hash is a great candidate for this. Alternatively you can
set `allow_unicode_keys` to support unicode keys, but beware of
what unicode encoding you use to make sure multiple clients can find the
same key.
Best Practices
---------------
- Always set the `connect_timeout` and `timeout` arguments in the
:py:class:`pymemcache.client.base.Client` constructor to avoid blocking
your process when memcached is slow. You might also want to enable the
`no_delay` option, which sets the TCP_NODELAY flag on the connection's
socket.
- Use the "noreply" flag for a significant performance boost. The "noreply"
flag is enabled by default for "set", "add", "replace", "append", "prepend",
and "delete". It is disabled by default for "cas", "incr" and "decr". It
obviously doesn't apply to any get calls.
- Use get_many and gets_many whenever possible, as they result in less
round trip times for fetching multiple keys.
- Use the "ignore_exc" flag to treat memcache/network errors as cache misses
on calls to the get* methods. This prevents failures in memcache, or network
errors, from killing your web requests. Do not use this flag if you need to
know about errors from memcache, and make sure you have some other way to
detect memcache server failures.
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