For the latest source code, see http://github.com/IlyaSkriblovsky/txredisapi
txredisapi is a non-blocking client driver for the redis
database, written in Python. It uses Twisted for
the asynchronous communication with redis.
It started as a fork of the original redis protocol for twisted, and evolved into a more robust, reliable, and complete solution for applications like web servers. These types of applications often need a fault-tolerant pool of connections with multiple redis servers, making it possible to easily develop and maintain distributed systems.
Most of the redis commands are supported, as well as other features such as silent reconnection, connection pools, and automatic sharding.
This driver is distributed as part of the cyclone web framework.
See CHANGELOG.md
Bear in mind that txredisapi.py is pure-python, in a single file.
Thus, there's absolutely no need to install it. Instead, just copy it to your
project directory and start using.
Latest source code is at https://github.com/IlyaSkriblovsky/txredisapi.
If you have cyclone, you probably already have it too. Try the following:
$ python
>>> import cyclone.redis
>>> cyclone.redis.version
'1.0'
However, if you really really insist in installing, get it from pypi:
pip install txredisapi
Twisted Trial unit tests
are available. Just start redis, and run trial ./tests.
If unix sockets are disabled in redis, it will silently skip those tests.
Make sure you run redis-cli flushall to clean up redis after the tests.
First thing to do is choose what type of connection you want. The driver supports single connection, connection pools, sharded connections (with automatic distribution based on a built-in consistent hashing algorithm), sharded connection pools, and all of these different types can be lazy, which is explained later (because I'm lazy now).
Basically, you want normal connections for simple batch clients that connect to redis, execute a couple of commands and disconnect - like crawlers, etc.
Example:
#!/usr/bin/env python
# coding: utf-8
import txredisapi as redis
from twisted.internet import defer
from twisted.internet import reactor
@defer.inlineCallbacks
def main():
rc = yield redis.Connection()
print rc
yield rc.set("foo", "bar")
v = yield rc.get("foo")
print "foo:", repr(v)
yield rc.disconnect()
if __name__ == "__main__":
main().addCallback(lambda ign: reactor.stop())
reactor.run()
Easily switch between redis.Connection() and redis.ConnectionPool()
with absolutely no changes to the logic of your program.
These are all the supported methods for connecting to Redis::
Connection(host, port, dbid, reconnect, charset)
lazyConnection(host, port, dbid, reconnect, charset)
ConnectionPool(host, port, dbid, poolsize, reconnect, charset)
lazyConnectionPool(host, port, dbid, poolsize, reconnect, charset)
ShardedConnection(hosts, dbid, reconnect, charset)
lazyShardedConnection(hosts, dbid, reconnect, charset)
ShardedConnectionPool(hosts, dbid, poolsize, reconnect, charset)
lazyShardedConnectionPool(hosts, dbid, poolsize, reconnect, charset)
UnixConnection(path, dbid, reconnect, charset)
lazyUnixConnection(path, dbid, reconnect, charset)
UnixConnectionPool(unix, dbid, poolsize, reconnect, charset)
lazyUnixConnectionPool(unix, dbid, poolsize, reconnect, charset)
ShardedUnixConnection(paths, dbid, reconnect, charset)
lazyShardedUnixConnection(paths, dbid, reconnect, charset)
ShardedUnixConnectionPool(paths, dbid, poolsize, reconnect, charset)
lazyShardedUnixConnectionPool(paths, dbid, poolsize, reconnect, charset)
The arguments are:
host:port pairs. [default: None]pathnames. [default: None]ClientContextFactory. [default: False]All connection methods return a connection handler object at some point.
Normal connections (not lazy) return a deferred, which is fired with the connection handler after the connection is established.
In case of connection pools, it will only fire the callback after all connections are set up, and ready.
Connection handler is the client interface with redis. It accepts all the
commands supported by redis, such as get, set, etc. It is the rc
object in the example below.
Connection handlers will automatically select one of the available connections in connection pools, and automatically reconnect to redis when necessary.
If the connection with redis is lost, all commands will raise the
ConnectionError exception, to indicate that there's no active connection.
However, if the reconnect argument was set to True during the
initialization, it will continuosly try to reconnect, in background.
Example:
#!/usr/bin/env python
# coding: utf-8
import txredisapi as redis
from twisted.internet import defer
from twisted.internet import reactor
def sleep(n):
d = defer.Deferred()
reactor.callLater(5, lambda *ign: d.callback(None))
return d
@defer.inlineCallbacks
def main():
rc = yield redis.ConnectionPool()
print rc
# set
yield rc.set("foo", "bar")
# sleep, so you can kill redis
print "sleeping for 5s, kill redis now..."
yield sleep(5)
try:
v = yield rc.get("foo")
print "foo:", v
yield rc.disconnect()
except redis.ConnectionError, e:
print str(e)
if __name__ == "__main__":
main().addCallback(lambda ign: reactor.stop())
reactor.run()
This type of connection will immediately return the connection handler object, even before the connection is made.
It will start the connection, (or connections, in case of connection pools) in background, and automatically reconnect if necessary.
You want lazy connections when you're writing servers, like web servers, or any other type of server that should not wait for the redis connection during the initialization of the program.
The example below is a web application, which will expose redis set, get and delete commands over HTTP.
If the database connection is down (either because redis is not running, or whatever reason), the web application will start normally. If connection is lost during the operation, nothing will change.
When there's no connection, all commands will fail, therefore the web application will respond with HTTP 503 (Service Unavailable). It will resume to normal once the connection with redis is re-established.
Try killing redis server after the application is running, and make a couple of requests. Then, start redis again and give it another try.
Example:
#!/usr/bin/env python
# coding: utf-8
import sys
import cyclone.web
import cyclone.redis
from twisted.internet import defer
from twisted.internet import reactor
from twisted.python import log
class Application(cyclone.web.Application):
def __init__(self):
handlers = [ (r"/text/(.+)", TextHandler) ]
RedisMixin.setup()
cyclone.web.Application.__init__(self, handlers, debug=True)
class RedisMixin(object):
redis_conn = None
@classmethod
def setup(self):
RedisMixin.redis_conn = cyclone.redis.lazyConnectionPool()
# Provide GET, SET and DELETE redis operations via HTTP
class TextHandler(cyclone.web.RequestHandler, RedisMixin):
@defer.inlineCallbacks
def get(self, key):
try:
value = yield self.redis_conn.get(key)
except Exception, e:
log.msg("Redis failed to get('%s'): %s" % (key, str(e)))
raise cyclone.web.HTTPError(503)
self.set_header("Content-Type", "text/plain")
self.write("%s=%s\r\n" % (key, value))
@defer.inlineCallbacks
def post(self, key):
value = self.get_argument("value")
try:
yield self.redis_conn.set(key, value)
except Exception, e:
log.msg("Redis failed to set('%s', '%s'): %s" % (key, value, str(e)))
raise cyclone.web.HTTPError(503)
self.set_header("Content-Type", "text/plain")
self.write("%s=%s\r\n" % (key, value))
@defer.inlineCallbacks
def delete(self, key):
try:
n = yield self.redis_conn.delete(key)
except Exception, e:
log.msg("Redis failed to del('%s'): %s" % (key, str(e)))
raise cyclone.web.HTTPError(503)
self.set_header("Content-Type", "text/plain")
self.write("DEL %s=%d\r\n" % (key, n))
def main():
log.startLogging(sys.stdout)
reactor.listenTCP(8888, Application(), interface="127.0.0.1")
reactor.run()
if __name__ == "__main__":
main()
This is the server running in one terminal::
$ ./helloworld.py
2012-02-17 15:40:25-0500 [-] Log opened.
2012-02-17 15:40:25-0500 [-] Starting factory <redis.Factory instance at 0x1012f0560>
2012-02-17 15:40:25-0500 [-] __main__.Application starting on 8888
2012-02-17 15:40:25-0500 [-] Starting factory <__main__.Application instance at 0x100f42290>
2012-02-17 15:40:53-0500 [RedisProtocol,client] 200 POST /text/foo (127.0.0.1) 1.20ms
2012-02-17 15:41:01-0500 [RedisProtocol,client] 200 GET /text/foo (127.0.0.1) 0.97ms
2012-02-17 15:41:09-0500 [RedisProtocol,client] 200 DELETE /text/foo (127.0.0.1) 0.65ms
(killed redis-server)
2012-02-17 15:48:48-0500 [HTTPConnection,0,127.0.0.1] Redis failed to get('foo'): Not connected
2012-02-17 15:48:48-0500 [HTTPConnection,0,127.0.0.1] 503 GET /text/foo (127.0.0.1) 2.99ms
And these are the requests, from curl in another terminal.
Set:
$ curl -D - -d "value=bar" http://localhost:8888/text/foo
HTTP/1.1 200 OK
Content-Length: 9
Content-Type: text/plain
foo=bar
Get:
$ curl -D - http://localhost:8888/text/foo
HTTP/1.1 200 OK
Content-Length: 9
Etag: "b63729aa7fa0e438eed735880951dcc21d733676"
Content-Type: text/plain
foo=bar
Delete:
$ curl -D - -X DELETE http://localhost:8888/text/foo
HTTP/1.1 200 OK
Content-Length: 11
Content-Type: text/plain
DEL foo=1
When redis is not running:
$ curl -D - http://localhost:8888/text/foo
HTTP/1.1 503 Service Unavailable
Content-Length: 89
Content-Type: text/html; charset=UTF-8
<html><title>503: Service Unavailable</title>
<body>503: Service Unavailable</body></html>
They can be normal, or lazy connections. They can be sharded connection pools. Not all commands are supported on sharded connections.
If the command you're trying to run is not supported on sharded connections,
the connection handler will raise the NotImplementedError exception.
Simple example with automatic sharding of keys between two redis servers:
#!/usr/bin/env python
# coding: utf-8
import txredisapi as redis
from twisted.internet import defer
from twisted.internet import reactor
@defer.inlineCallbacks
def main():
rc = yield redis.ShardedConnection(["localhost:6379", "localhost:6380"])
print rc
print "Supported methods on sharded connections:", rc.ShardedMethods
keys = []
for x in xrange(100):
key = "foo%02d" % x
yield rc.set(key, "bar%02d" % x)
keys.append(key)
# yey! mget is supported!
response = yield rc.mget(keys)
for val in response:
print val
yield rc.disconnect()
if __name__ == "__main__":
main().addCallback(lambda ign: reactor.stop())
reactor.run()
For obvious reasons, transactions are NOT supported on sharded connections. But they work pretty good on normal or lazy connections, and connection pools.
NOTE: redis uses the following methods for transactions:
Because exec is a reserved word in Python, the command to commit is
commit.
Example:
#!/usr/bin/env python
# coding: utf-8
import txredisapi as redis
from twisted.internet import defer
from twisted.internet import reactor
@defer.inlineCallbacks
def main():
rc = yield redis.ConnectionPool()
# Remove the keys
yield rc.delete(["a1", "a2", "a3"])
# Start transaction
t = yield rc.multi()
# These will return "QUEUED" - even t.get(key)
yield t.set("a1", "1")
yield t.set("a2", "2")
yield t.set("a3", "3")
yield t.get("a1")
# Try to call get() while in a transaction.
# It will fail if it's not a connection pool, or if all connections
# in the pool are in a transaction.
# Note that it's rc.get(), not the transaction object t.get().
try:
v = yield rc.get("foo")
print "foo=", v
except Exception, e:
print "can't get foo:", e
# Commit, and get all responses from transaction.
r = yield t.commit()
print "commit=", repr(r)
yield rc.disconnect()
if __name__ == "__main__":
main().addCallback(lambda ign: reactor.stop())
reactor.run()
A "COUNTER" example, using WATCH/MULTI:
#!/usr/bin/env python
# coding: utf-8
import txredisapi as redis
from twisted.internet import defer
from twisted.internet import reactor
@defer.inlineCallbacks
def main():
rc = yield redis.ConnectionPool()
# Reset keys
yield rc.set("a1", 0)
# Synchronize and start transaction
t = yield rc.watch("a1")
# Load previous value
a1 = yield t.get("a1")
# start the transactional pipeline
yield t.multi()
# modify and retrieve the new a1 value
yield t.set("a1", a1 + 1)
yield t.get("a1")
print "simulating concurrency, this will abort the transaction"
yield rc.set("a1", 2)
try:
r = yield t.commit()
print "commit=", repr(r)
except redis.WatchError, e:
a1 = yield rc.get("a1")
print "transaction has failed."
print "current a1 value: ", a1
yield rc.disconnect()
if __name__ == "__main__":
main().addCallback(lambda ign: reactor.stop())
reactor.run()
Calling commit will cause it to return a list with the return of all
commands executed in the transaction. discard, on the other hand, will
normally return just an OK.
txredisapi automatically pipelines all commands by sending next commands without waiting for the previous one to receive reply from server. This works even on single connections and increases performance by reducing number of round-trip delays and. There are two exceptions, though:
blpop, brpop or brpoplpush until
response is received;multi/commit are also blocking connection making all other
commands to wait until transaction is executed.When you need to load tons of data to Redis it might be more effective to sent
commands in batches grouping them together offline to save on TCP packets and network
stack overhead. You can do this using pipeline method to explicitly accumulate
commands and send them to server in a single batch. Be careful to not accumulate too
many commands: unreasonable batch size may eat up unexpected amount of memory on both
client and server side. Group commands in batches of, for example, 10k commands instead
of sending all your data at once. The speed will be nearly the same, but the additional
memory used will be at max the amount needed to queue this 10k commands
To send commands in a batch:
#!/usr/bin/env python
# coding: utf-8
import txredisapi as redis
from twisted.internet import defer
from twisted.internet import reactor
@defer.inlineCallbacks
def main():
rc = yield redis.ConnectionPool()
# Start grouping commands
pipeline = yield rc.pipeline()
pipeline.set("foo", 123)
pipeline.set("bar", 987)
pipeline.get("foo")
pipeline.get("bar")
# Write those 2 sets and 2 gets to redis all at once, and wait
# for all replies before continuing.
results = yield pipeline.execute_pipeline()
print "foo:", results[2] # should be 123
print "bar:", results[3] # should be 987
yield rc.disconnect()
if __name__ == "__main__":
main().addCallback(lambda ign: reactor.stop())
reactor.run()
This is how to authenticate::
#!/usr/bin/env python
import txredisapi
from twisted.internet import defer
from twisted.internet import reactor
@defer.inlineCallbacks
def main():
redis = yield txredisapi.Connection(password="foobared")
yield redis.set("foo", "bar")
print (yield redis.get("foo"))
reactor.stop()
if __name__ == "__main__":
main()
reactor.run()
txredisapi can discover Redis master and slaves addresses using
Redis Sentinel and automatically failover
in case of server failure.
#!/usr/bin/env python
from twisted.internet.task import react
import txredisapi
@defer.inlineCallbacks
def main(reactor):
sentinel = txredisapi.Sentinel([("sentinel-a", 26379), ("sentinel-b", 26379), ("sentinel-c", 26379)])
redis = sentinel.master_for("service_name")
yield redis.set("foo", "bar")
print (yield redis.get("foo"))
yield redis.disconnect()
yield sentinel.disconnect()
react(main)
Usual connection arguments like dbid=N or poolsize=N can be specified in
master_for() call. Use sentinel.slave_for() to connect to one of the slaves
instead of master.
Add min_other_sentinels=N to Sentinel constructor call to make it obey information
only from sentinels that currently connected to specified number of other sentinels
to minimize a risk of split-brain in case of network partitioning.
Thanks to (in no particular order):
Alexandre Fiori
Gleicon Moraes
Dorian Raymer and Ludovico Magnocavallo
Vanderson Mota
Jeethu Rao
Jeremy Archer
Christoph Tavan (@ctavan)
dgvncsz0f
Ilia Glazkov
Matt Pizzimenti (mjpizz)
Nickolai Novik (jettify)
Evgeny Tataurov (etataurov)
Ilya Skriblovsky (IlyaSkriblovsky)
FAQs
non-blocking redis client for python
We found that txredisapi demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 2 open source maintainers collaborating on the project.
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