From 980dfa5484140bc676246e0469a7c34b6b130a50 Mon Sep 17 00:00:00 2001 From: "Chayim I. Kirshen" Date: Tue, 19 Jul 2022 11:29:28 +0300 Subject: [PATCH 1/2] cleaning up the readme and moving docs into readthedocs --- README.md | 1144 ++---------------------------------- docs/advanced_features.rst | 436 ++++++++++++++ docs/clustering.rst | 242 ++++++++ docs/index.rst | 3 + docs/lua_scripting.rst | 110 ++++ redis/client.py | 2 + 6 files changed, 828 insertions(+), 1109 deletions(-) create mode 100644 docs/advanced_features.rst create mode 100644 docs/clustering.rst create mode 100644 docs/lua_scripting.rst diff --git a/README.md b/README.md index 4241da47dd..d4f324209a 100644 --- a/README.md +++ b/README.md @@ -27,18 +27,19 @@ To install redis-py, simply: $ pip install redis ``` -Looking for a high-level library to handle object mapping? See [redis-om-python](https://github.com/redis/redis-om-python)! +For faster performance, install redis with hiredis support, this provides a compiled response parser, and *for most cases* requires zero code changes. By default, if hiredis is available, redis-py will attempt to use it for response parsing. -redis-py requires a running Redis server. Assuming you have docker -```bash -docker run -p 6379:6379 -it redis/redis-stack-server:latest +``` bash +$ pip install redis[hiredis] ``` -## Getting Started +Looking for a high-level library to handle object mapping? See [redis-om-python](https://github.com/redis/redis-om-python)! -redis-py supports Python 3.7+. +## Usage -``` pycon +### Basic Example + +``` python >>> import redis >>> r = redis.Redis(host='localhost', port=6379, db=0) >>> r.set('foo', 'bar') @@ -47,34 +48,34 @@ True b'bar' ``` -By default, all responses are returned as bytes in Python -3. +The above code connects to localhost on port 6379, sets a value in Redis, and retrieves it. All responses are returned as bytes in Python, to receive decoded strings, set *decode_responses=True*. For this, and more connection options, see [these examples](https://redis.readthedocs.io/en/stable/examples.html) -If **all** string responses from a client should be decoded, the user -can specify *decode_responses=True* in -```Redis.__init__```. In this case, any Redis command that -returns a string type will be decoded with the encoding -specified. +### Connection Pools -The default encoding is utf-8, but this can be customized by specifying the -encoding argument for the redis.Redis class. -The encoding will be used to automatically encode any -strings passed to commands, such as key names and values. +By default, redis-py uses a connection pool to manage connections. Each instance of of a Redis class receives its own connection pool. You can however define your own [redis.ConnectionPool](https://redis.readthedocs.io/en/stable/connections.html#connection-pools) + +``` python +>>> pool = redis.ConnectionPool(host='localhost', port=6379, db=0) +>>> r = redis.Redis(connection_pool=pool) +``` -## API Reference +Alternatively, you might want to look at [Async connections](https://redis.readthedocs.io/en/stable/examples/asyncio_examples.html), or [Cluster connections](https://redis.readthedocs.io/en/stable/connections.html#cluster-client), or even [Async Cluster connections](https://redis.readthedocs.io/en/stable/connections.html#async-cluster-client) + +### Redis Commands + +There is built-in support for all of the [out-of-the-box Redis commands](https://redis.io/commands). They are exposed using the raw Redis command names (`HSET`, `HGETALL`, etc.) except where a work (i.e del) is reserved by the language. The complete set of commands can be found [here](https://github.com/redis/redis-py/tree/master/redis/commands), or [the documentation](https://redis.readthedocs.io/en/stable/commands.html). + +## Advanced Topics The [official Redis command documentation](https://redis.io/commands) does a great job of explaining each command in detail. redis-py attempts to adhere to the official command syntax. There are a few exceptions: -- **SELECT**: Not implemented. See the explanation in the Thread - Safety section below. -- **DEL**: *del* is a reserved keyword in the Python syntax. - Therefore redis-py uses *delete* instead. - **MULTI/EXEC**: These are implemented as part of the Pipeline class. The pipeline is wrapped with the MULTI and EXEC statements by default when it is executed, which can be disabled by specifying transaction=False. See more about Pipelines below. + - **SUBSCRIBE/LISTEN**: Similar to pipelines, PubSub is implemented as a separate class as it places the underlying connection in a state where it can\'t execute non-pubsub commands. Calling the pubsub @@ -83,1112 +84,37 @@ to adhere to the official command syntax. There are a few exceptions: PUBLISH from the Redis client (see [this comment on issue #151](https://github.com/redis/redis-py/issues/151#issuecomment-1545015) for details). -- **SCAN/SSCAN/HSCAN/ZSCAN**: The *SCAN commands are implemented as - they exist in the Redis documentation. In addition, each command has - an equivalent iterator method. These are purely for convenience so - the user doesn't have to keep track of the cursor while iterating. - Use the scan_iter/sscan_iter/hscan_iter/zscan_iter methods for this - behavior. - -## Connecting to Redis - -### Client Classes: Redis and StrictRedis - -redis-py 3.0 drops support for the legacy *Redis* client class. -*StrictRedis* has been renamed to *Redis* and an alias named -*StrictRedis* is provided so that users previously using -*StrictRedis* can continue to run unchanged. - -The 2.X *Redis* class provided alternative implementations of a few -commands. This confused users (rightfully so) and caused a number of -support issues. To make things easier going forward, it was decided to -drop support for these alternate implementations and instead focus on a -single client class. - -2.X users that are already using StrictRedis don\'t have to change the -class name. StrictRedis will continue to work for the foreseeable -future. - -2.X users that are using the Redis class will have to make changes if -they use any of the following commands: - -- SETEX: The argument order has changed. The new order is (name, time, - value). -- LREM: The argument order has changed. The new order is (name, num, - value). -- TTL and PTTL: The return value is now always an int and matches the - official Redis command (>0 indicates the timeout, -1 indicates that - the key exists but that it has no expire time set, -2 indicates that - the key does not exist) - - -### 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 -fine-grain control of how connections are managed. - -``` pycon ->>> pool = redis.ConnectionPool(host='localhost', port=6379, db=0) ->>> r = redis.Redis(connection_pool=pool) -``` - -### Connections - -ConnectionPools manage a set of Connection instances. redis-py ships -with two types of Connections. The default, Connection, is a normal TCP -socket based connection. The UnixDomainSocketConnection allows for -clients running on the same device as the server to connect via a unix -domain socket. To use a UnixDomainSocketConnection connection, simply -pass the unix_socket_path argument, which is a string to the unix domain -socket file. Additionally, make sure the unixsocket parameter is defined -in your redis.conf file. It\'s commented out by default. - -``` pycon ->>> r = redis.Redis(unix_socket_path='/tmp/redis.sock') -``` - -You can create your own Connection subclasses as well. This may be -useful if you want to control the socket behavior within an async -framework. To instantiate a client class using your own connection, you -need to create a connection pool, passing your class to the -connection_class argument. Other keyword parameters you pass to the pool -will be passed to the class specified during initialization. - -``` pycon ->>> pool = redis.ConnectionPool(connection_class=YourConnectionClass, - your_arg='...', ...) -``` - -Connections maintain an open socket to the Redis server. Sometimes these -sockets are interrupted or disconnected for a variety of reasons. For -example, network appliances, load balancers and other services that sit -between clients and servers are often configured to kill connections -that remain idle for a given threshold. - -When a connection becomes disconnected, the next command issued on that -connection will fail and redis-py will raise a ConnectionError to the -caller. This allows each application that uses redis-py to handle errors -in a way that\'s fitting for that specific application. However, -constant error handling can be verbose and cumbersome, especially when -socket disconnections happen frequently in many production environments. - -To combat this, redis-py can issue regular health checks to assess the -liveliness of a connection just before issuing a command. Users can pass -`health_check_interval=N` to the Redis or ConnectionPool classes or as a -query argument within a Redis URL. The value of `health_check_interval` -must be an integer. A value of `0`, the default, disables health checks. -Any positive integer will enable health checks. Health checks are -performed just before a command is executed if the underlying connection -has been idle for more than `health_check_interval` seconds. For -example, `health_check_interval=30` will ensure that a health check is -run on any connection that has been idle for 30 or more seconds just -before a command is executed on that connection. - -If your application is running in an environment that disconnects idle -connections after 30 seconds you should set the `health_check_interval` -option to a value less than 30. - -This option also works on any PubSub connection that is created from a -client with `health_check_interval` enabled. PubSub users need to ensure -that *get_message()* or `listen()` are called more frequently than -`health_check_interval` seconds. It is assumed that most workloads -already do this. - -If your PubSub use case doesn\'t call `get_message()` or `listen()` -frequently, you should call `pubsub.check_health()` explicitly on a -regularly basis. - -### SSL Connections - -redis-py 3.0 changes the default value of the -ssl_cert_reqs option from None to -\'required\'. See [Issue -1016](https://github.com/redis/redis-py/issues/1016). This change -enforces hostname validation when accepting a cert from a remote SSL -terminator. If the terminator doesn\'t properly set the hostname on the -cert this will cause redis-py 3.0 to raise a ConnectionError. - -This check can be disabled by setting ssl_cert_reqs to -None. Note that doing so removes the security check. Do so -at your own risk. - -Example with hostname verification using a local certificate bundle -(linux): - -``` pycon ->>> import redis ->>> r = redis.Redis(host='xxxxxx.cache.amazonaws.com', port=6379, db=0, - ssl=True, - ssl_ca_certs='/etc/ssl/certs/ca-certificates.crt') ->>> r.set('foo', 'bar') -True ->>> r.get('foo') -b'bar' -``` - -Example with hostname verification using -[certifi](https://pypi.org/project/certifi/): - -``` pycon ->>> import redis, certifi ->>> r = redis.Redis(host='xxxxxx.cache.amazonaws.com', port=6379, db=0, - ssl=True, ssl_ca_certs=certifi.where()) ->>> r.set('foo', 'bar') -True ->>> r.get('foo') -b'bar' -``` - -Example turning off hostname verification (not recommended): - -``` pycon ->>> import redis ->>> r = redis.Redis(host='xxxxxx.cache.amazonaws.com', port=6379, db=0, - ssl=True, ssl_cert_reqs=None) ->>> r.set('foo', 'bar') -True ->>> r.get('foo') -b'bar' -``` - -### Sentinel support -redis-py can be used together with [Redis -Sentinel](https://redis.io/topics/sentinel) to discover Redis nodes. You -need to have at least one Sentinel daemon running in order to use -redis-py's Sentinel support. - -Connecting redis-py to the Sentinel instance(s) is easy. You can use a -Sentinel connection to discover the master and slaves network addresses: - -``` pycon ->>> from redis import Sentinel ->>> sentinel = Sentinel([('localhost', 26379)], socket_timeout=0.1) ->>> sentinel.discover_master('mymaster') -('127.0.0.1', 6379) ->>> sentinel.discover_slaves('mymaster') -[('127.0.0.1', 6380)] -``` - -To connect to a sentinel which uses SSL ([see SSL -connections](#ssl-connections) for more examples of SSL configurations): - -``` pycon ->>> from redis import Sentinel ->>> sentinel = Sentinel([('localhost', 26379)], - ssl=True, - ssl_ca_certs='/etc/ssl/certs/ca-certificates.crt') ->>> sentinel.discover_master('mymaster') -('127.0.0.1', 6379) -``` - -You can also create Redis client connections from a Sentinel instance. -You can connect to either the master (for write operations) or a slave -(for read-only operations). - -``` pycon ->>> master = sentinel.master_for('mymaster', socket_timeout=0.1) ->>> slave = sentinel.slave_for('mymaster', socket_timeout=0.1) ->>> master.set('foo', 'bar') ->>> slave.get('foo') -b'bar' -``` - -The master and slave objects are normal Redis instances with their -connection pool bound to the Sentinel instance. When a Sentinel backed -client attempts to establish a connection, it first queries the Sentinel -servers to determine an appropriate host to connect to. If no server is -found, a MasterNotFoundError or SlaveNotFoundError is raised. Both -exceptions are subclasses of ConnectionError. - -When trying to connect to a slave client, the Sentinel connection pool -will iterate over the list of slaves until it finds one that can be -connected to. If no slaves can be connected to, a connection will be -established with the master. - -See [Guidelines for Redis clients with support for Redis -Sentinel](https://redis.io/topics/sentinel-clients) to learn more about -Redis Sentinel. - --------------------------- - -### Parsers - -Parser classes provide a way to control how responses from the Redis -server are parsed. redis-py ships with two parser classes, the -PythonParser and the HiredisParser. By default, redis-py will attempt to -use the HiredisParser if you have the hiredis module installed and will -fallback to the PythonParser otherwise. - -Hiredis is a C library maintained by the core Redis team. Pieter -Noordhuis was kind enough to create Python bindings. Using Hiredis can -provide up to a 10x speed improvement in parsing responses from the -Redis server. The performance increase is most noticeable when -retrieving many pieces of data, such as from LRANGE or SMEMBERS -operations. - -Hiredis is available on PyPI, and can be installed via pip just like -redis-py. - -``` bash -$ pip install hiredis -``` - -### Response Callbacks - -The client class uses a set of callbacks to cast Redis responses to the -appropriate Python type. There are a number of these callbacks defined -on the Redis client class in a dictionary called RESPONSE_CALLBACKS. - -Custom callbacks can be added on a per-instance basis using the -set_response_callback method. This method accepts two arguments: a -command name and the callback. Callbacks added in this manner are only -valid on the instance the callback is added to. If you want to define or -override a callback globally, you should make a subclass of the Redis -client and add your callback to its RESPONSE_CALLBACKS class dictionary. - -Response callbacks take at least one parameter: the response from the -Redis server. Keyword arguments may also be accepted in order to further -control how to interpret the response. These keyword arguments are -specified during the command\'s call to execute_command. The ZRANGE -implementation demonstrates the use of response callback keyword -arguments with its \"withscores\" argument. - -### Thread Safety - -Redis client instances can safely be shared between threads. Internally, -connection instances are only retrieved from the connection pool during -command execution, and returned to the pool directly after. Command -execution never modifies state on the client instance. - -However, there is one caveat: the Redis SELECT command. The SELECT -command allows you to switch the database currently in use by the -connection. That database remains selected until another is selected or -until the connection is closed. This creates an issue in that -connections could be returned to the pool that are connected to a -different database. - -As a result, redis-py does not implement the SELECT command on client -instances. If you use multiple Redis databases within the same -application, you should create a separate client instance (and possibly -a separate connection pool) for each database. - -It is not safe to pass PubSub or Pipeline objects between threads. +For more details, please see the documentation on [advanced topics page](https://redis.readthedocs.io/en/stable/advanced_features.html). ### Pipelines -Pipelines are a subclass of the base Redis class that provide support -for buffering multiple commands to the server in a single request. They -can be used to dramatically increase the performance of groups of -commands by reducing the number of back-and-forth TCP packets between -the client and server. +The following is a basic example of a [Redis pipeline](https://redis.io/docs/manual/pipelining/), a method to optimize round-trip calls, by batching Redis commands, and receiving their results as a list. -Pipelines are quite simple to use: -``` pycon ->>> r = redis.Redis(...) ->>> r.set('bing', 'baz') ->>> # Use the pipeline() method to create a pipeline instance +``` python >>> pipe = r.pipeline() ->>> # The following SET commands are buffered ->>> pipe.set('foo', 'bar') ->>> pipe.get('bing') ->>> # the EXECUTE call sends all buffered commands to the server, returning ->>> # a list of responses, one for each command. +>>> pipe.set('foo', 5) +>>> pipe.set('bar', 18.5) +>>> pipe.set('blee', "hello world!") >>> pipe.execute() -[True, b'baz'] -``` - -For ease of use, all commands being buffered into the pipeline return -the pipeline object itself. Therefore calls can be chained like: - -``` pycon ->>> pipe.set('foo', 'bar').sadd('faz', 'baz').incr('auto_number').execute() -[True, True, 6] -``` - -In addition, pipelines can also ensure the buffered commands are -executed atomically as a group. This happens by default. If you want to -disable the atomic nature of a pipeline but still want to buffer -commands, you can turn off transactions. - -``` pycon ->>> pipe = r.pipeline(transaction=False) -``` - -A common issue occurs when requiring atomic transactions but needing to -retrieve values in Redis prior for use within the transaction. For -instance, let\'s assume that the INCR command didn\'t exist and we need -to build an atomic version of INCR in Python. - -The completely naive implementation could GET the value, increment it in -Python, and SET the new value back. However, this is not atomic because -multiple clients could be doing this at the same time, each getting the -same value from GET. - -Enter the WATCH command. WATCH provides the ability to monitor one or -more keys prior to starting a transaction. If any of those keys change -prior the execution of that transaction, the entire transaction will be -canceled and a WatchError will be raised. To implement our own -client-side INCR command, we could do something like this: - -``` pycon ->>> with r.pipeline() as pipe: -... while True: -... try: -... # put a WATCH on the key that holds our sequence value -... pipe.watch('OUR-SEQUENCE-KEY') -... # after WATCHing, the pipeline is put into immediate execution -... # mode until we tell it to start buffering commands again. -... # this allows us to get the current value of our sequence -... current_value = pipe.get('OUR-SEQUENCE-KEY') -... next_value = int(current_value) + 1 -... # now we can put the pipeline back into buffered mode with MULTI -... pipe.multi() -... pipe.set('OUR-SEQUENCE-KEY', next_value) -... # and finally, execute the pipeline (the set command) -... pipe.execute() -... # if a WatchError wasn't raised during execution, everything -... # we just did happened atomically. -... break -... except WatchError: -... # another client must have changed 'OUR-SEQUENCE-KEY' between -... # the time we started WATCHing it and the pipeline's execution. -... # our best bet is to just retry. -... continue -``` - -Note that, because the Pipeline must bind to a single connection for the -duration of a WATCH, care must be taken to ensure that the connection is -returned to the connection pool by calling the reset() method. If the -Pipeline is used as a context manager (as in the example above) reset() -will be called automatically. Of course you can do this the manual way -by explicitly calling reset(): - -``` pycon ->>> pipe = r.pipeline() ->>> while True: -... try: -... pipe.watch('OUR-SEQUENCE-KEY') -... ... -... pipe.execute() -... break -... except WatchError: -... continue -... finally: -... pipe.reset() -``` - -A convenience method named \"transaction\" exists for handling all the -boilerplate of handling and retrying watch errors. It takes a callable -that should expect a single parameter, a pipeline object, and any number -of keys to be WATCHed. Our client-side INCR command above can be written -like this, which is much easier to read: - -``` pycon ->>> def client_side_incr(pipe): -... current_value = pipe.get('OUR-SEQUENCE-KEY') -... next_value = int(current_value) + 1 -... pipe.multi() -... pipe.set('OUR-SEQUENCE-KEY', next_value) ->>> ->>> r.transaction(client_side_incr, 'OUR-SEQUENCE-KEY') -[True] +[True, True, True] ``` -Be sure to call pipe.multi() in the callable passed to -Redis.transaction prior to any write commands. +### PubSub -### Publish / Subscribe +The following example shows how to utilize [Redis Pub/Sub](https://redis.io/docs/manual/pubsub/) to subscribe to specific channels. -redis-py includes a PubSub object that subscribes to -channels and listens for new messages. Creating a PubSub -object is easy. - -``` pycon +``` python >>> r = redis.Redis(...) >>> p = r.pubsub() -``` - -Once a PubSub instance is created, channels and patterns -can be subscribed to. - -``` pycon >>> p.subscribe('my-first-channel', 'my-second-channel', ...) ->>> p.psubscribe('my-*', ...) -``` - -The PubSub instance is now subscribed to those -channels/patterns. The subscription confirmations can be seen by reading -messages from the PubSub instance. - -``` pycon >>> p.get_message() {'pattern': None, 'type': 'subscribe', 'channel': b'my-second-channel', 'data': 1} ->>> p.get_message() -{'pattern': None, 'type': 'subscribe', 'channel': b'my-first-channel', 'data': 2} ->>> p.get_message() -{'pattern': None, 'type': 'psubscribe', 'channel': b'my-*', 'data': 3} ``` -Every message read from a PubSub instance will be a -dictionary with the following keys. -- **type**: One of the following: \'subscribe\', \'unsubscribe\', - \'psubscribe\', \'punsubscribe\', \'message\', \'pmessage\' -- **channel**: The channel \[un\]subscribed to or the channel a - message was published to -- **pattern**: The pattern that matched a published message\'s - channel. Will be None in all cases except for - \'pmessage\' types. -- **data**: The message data. With \[un\]subscribe messages, this - value will be the number of channels and patterns the connection is - currently subscribed to. With \[p\]message messages, this value will - be the actual published message. - -Let\'s send a message now. - -``` pycon -# the publish method returns the number matching channel and pattern -# subscriptions. 'my-first-channel' matches both the 'my-first-channel' -# subscription and the 'my-*' pattern subscription, so this message will -# be delivered to 2 channels/patterns ->>> r.publish('my-first-channel', 'some data') -2 ->>> p.get_message() -{'channel': b'my-first-channel', 'data': b'some data', 'pattern': None, 'type': 'message'} ->>> p.get_message() -{'channel': b'my-first-channel', 'data': b'some data', 'pattern': b'my-*', 'type': 'pmessage'} -``` - -Unsubscribing works just like subscribing. If no arguments are passed to -\[p\]unsubscribe, all channels or patterns will be unsubscribed from. - -``` pycon ->>> p.unsubscribe() ->>> p.punsubscribe('my-*') ->>> p.get_message() -{'channel': b'my-second-channel', 'data': 2, 'pattern': None, 'type': 'unsubscribe'} ->>> p.get_message() -{'channel': b'my-first-channel', 'data': 1, 'pattern': None, 'type': 'unsubscribe'} ->>> p.get_message() -{'channel': b'my-*', 'data': 0, 'pattern': None, 'type': 'punsubscribe'} -``` - -redis-py also allows you to register callback functions to handle -published messages. Message handlers take a single argument, the -message, which is a dictionary just like the examples above. To -subscribe to a channel or pattern with a message handler, pass the -channel or pattern name as a keyword argument with its value being the -callback function. - -When a message is read on a channel or pattern with a message handler, -the message dictionary is created and passed to the message handler. In -this case, a None value is returned from get_message() -since the message was already handled. - -``` pycon ->>> def my_handler(message): -... print('MY HANDLER: ', message['data']) ->>> p.subscribe(**{'my-channel': my_handler}) -# read the subscribe confirmation message ->>> p.get_message() -{'pattern': None, 'type': 'subscribe', 'channel': b'my-channel', 'data': 1} ->>> r.publish('my-channel', 'awesome data') -1 -# for the message handler to work, we need tell the instance to read data. -# this can be done in several ways (read more below). we'll just use -# the familiar get_message() function for now ->>> message = p.get_message() -MY HANDLER: awesome data -# note here that the my_handler callback printed the string above. -# `message` is None because the message was handled by our handler. ->>> print(message) -None -``` - -If your application is not interested in the (sometimes noisy) -subscribe/unsubscribe confirmation messages, you can ignore them by -passing ignore_subscribe_messages=True to -r.pubsub(). This will cause all subscribe/unsubscribe -messages to be read, but they won\'t bubble up to your application. - -``` pycon ->>> p = r.pubsub(ignore_subscribe_messages=True) ->>> p.subscribe('my-channel') ->>> p.get_message() # hides the subscribe message and returns None ->>> r.publish('my-channel', 'my data') -1 ->>> p.get_message() -{'channel': b'my-channel', 'data': b'my data', 'pattern': None, 'type': 'message'} -``` - -There are three different strategies for reading messages. - -The examples above have been using pubsub.get_message(). -Behind the scenes, get_message() uses the system\'s -\'select\' module to quickly poll the connection\'s socket. If there\'s -data available to be read, get_message() will read it, -format the message and return it or pass it to a message handler. If -there\'s no data to be read, get_message() will -immediately return None. This makes it trivial to integrate into an -existing event loop inside your application. - -``` pycon ->>> while True: ->>> message = p.get_message() ->>> if message: ->>> # do something with the message ->>> time.sleep(0.001) # be nice to the system :) -``` - -Older versions of redis-py only read messages with -pubsub.listen(). listen() is a generator that blocks until -a message is available. If your application doesn\'t need to do anything -else but receive and act on messages received from redis, listen() is an -easy way to get up an running. - -``` pycon ->>> for message in p.listen(): -... # do something with the message -``` - -The third option runs an event loop in a separate thread. -pubsub.run_in_thread() creates a new thread and starts the -event loop. The thread object is returned to the caller of -[un_in_thread(). The caller can use the -thread.stop() method to shut down the event loop and -thread. Behind the scenes, this is simply a wrapper around -get_message() that runs in a separate thread, essentially -creating a tiny non-blocking event loop for you. -run_in_thread() takes an optional sleep_time -argument. If specified, the event loop will call -time.sleep() with the value in each iteration of the loop. - -Note: Since we\'re running in a separate thread, there\'s no way to -handle messages that aren\'t automatically handled with registered -message handlers. Therefore, redis-py prevents you from calling -run_in_thread() if you\'re subscribed to patterns or -channels that don\'t have message handlers attached. - -``` pycon ->>> p.subscribe(**{'my-channel': my_handler}) ->>> thread = p.run_in_thread(sleep_time=0.001) -# the event loop is now running in the background processing messages -# when it's time to shut it down... ->>> thread.stop() -``` - -run_in_thread also supports an optional exception handler, -which lets you catch exceptions that occur within the worker thread and -handle them appropriately. The exception handler will take as arguments -the exception itself, the pubsub object, and the worker thread returned -by run_in_thread. - -``` pycon ->>> p.subscribe(**{'my-channel': my_handler}) ->>> def exception_handler(ex, pubsub, thread): ->>> print(ex) ->>> thread.stop() ->>> thread.join(timeout=1.0) ->>> pubsub.close() ->>> thread = p.run_in_thread(exception_handler=exception_handler) -``` - -A PubSub object adheres to the same encoding semantics as the client -instance it was created from. Any channel or pattern that\'s unicode -will be encoded using the charset specified on the client -before being sent to Redis. If the client\'s -decode_responses flag is set the False (the default), the -\'channel\', \'pattern\' and \'data\' values in message dictionaries -will be byte strings (str on Python 2, bytes on Python 3). If the -client\'s decode_responses is True, then the \'channel\', -\'pattern\' and \'data\' values will be automatically decoded to unicode -strings using the client\'s charset. - -PubSub objects remember what channels and patterns they are subscribed -to. In the event of a disconnection such as a network error or timeout, -the PubSub object will re-subscribe to all prior channels and patterns -when reconnecting. Messages that were published while the client was -disconnected cannot be delivered. When you\'re finished with a PubSub -object, call its .close() method to shutdown the -connection. - -``` pycon ->>> p = r.pubsub() ->>> ... ->>> p.close() -``` - -The PUBSUB set of subcommands CHANNELS, NUMSUB and NUMPAT are also -supported: - -``` pycon ->>> r.pubsub_channels() -[b'foo', b'bar'] ->>> r.pubsub_numsub('foo', 'bar') -[(b'foo', 9001), (b'bar', 42)] ->>> r.pubsub_numsub('baz') -[(b'baz', 0)] ->>> r.pubsub_numpat() -1204 -``` - -### Monitor - -redis-py includes a Monitor object that streams every -command processed by the Redis server. Use listen() on the -Monitor object to block until a command is received. - -``` pycon ->>> r = redis.Redis(...) ->>> with r.monitor() as m: ->>> for command in m.listen(): ->>> print(command) -``` - -### Lua Scripting - -redis-py supports the EVAL, EVALSHA, and SCRIPT commands. However, there -are a number of edge cases that make these commands tedious to use in -real world scenarios. Therefore, redis-py exposes a Script object that -makes scripting much easier to use. (RedisClusters have limited support for -scripting.) - -To create a Script instance, use the register_script -function on a client instance passing the Lua code as the first -argument. register_script returns a Script instance that -you can use throughout your code. - -The following trivial Lua script accepts two parameters: the name of a -key and a multiplier value. The script fetches the value stored in the -key, multiplies it with the multiplier value and returns the result. - -``` pycon ->>> r = redis.Redis() ->>> lua = """ -... local value = redis.call('GET', KEYS[1]) -... value = tonumber(value) -... return value * ARGV[1]""" ->>> multiply = r.register_script(lua) -``` - -multiply is now a Script instance that is invoked by -calling it like a function. Script instances accept the following -optional arguments: - -- **keys**: A list of key names that the script will access. This - becomes the KEYS list in Lua. -- **args**: A list of argument values. This becomes the ARGV list in - Lua. -- **client**: A redis-py Client or Pipeline instance that will invoke - the script. If client isn\'t specified, the client that initially - created the Script instance (the one that - register_script was invoked from) will be used. - -Continuing the example from above: - -``` pycon ->>> r.set('foo', 2) ->>> multiply(keys=['foo'], args=[5]) -10 -``` - -The value of key \'foo\' is set to 2. When multiply is invoked, the -\'foo\' key is passed to the script along with the multiplier value of -5. Lua executes the script and returns the result, 10. - -Script instances can be executed using a different client instance, even -one that points to a completely different Redis server. - -``` pycon ->>> r2 = redis.Redis('redis2.example.com') ->>> r2.set('foo', 3) ->>> multiply(keys=['foo'], args=[5], client=r2) -15 -``` - -The Script object ensures that the Lua script is loaded into Redis\'s -script cache. In the event of a NOSCRIPT error, it will load the script -and retry executing it. - -Script objects can also be used in pipelines. The pipeline instance -should be passed as the client argument when calling the script. Care is -taken to ensure that the script is registered in Redis\'s script cache -just prior to pipeline execution. - -``` pycon ->>> pipe = r.pipeline() ->>> pipe.set('foo', 5) ->>> multiply(keys=['foo'], args=[5], client=pipe) ->>> pipe.execute() -[True, 25] -``` - - -### Scan Iterators - -The \*SCAN commands introduced in Redis 2.8 can be cumbersome to use. -While these commands are fully supported, redis-py also exposes the -following methods that return Python iterators for convenience: -scan_iter, hscan_iter, -sscan_iter and zscan_iter. - -``` pycon ->>> for key, value in (('A', '1'), ('B', '2'), ('C', '3')): -... r.set(key, value) ->>> for key in r.scan_iter(): -... print(key, r.get(key)) -A 1 -B 2 -C 3 -``` - -### Cluster Mode - -redis-py now supports cluster mode and provides a client for -[Redis Cluster](). - -The cluster client is based on Grokzen's -[redis-py-cluster](https://github.com/Grokzen/redis-py-cluster), has added bug -fixes, and now supersedes that library. Support for these changes is thanks to -his contributions. - -To learn more about Redis Cluster, see -[Redis Cluster specifications](https://redis.io/topics/cluster-spec). - -**Create RedisCluster:** - -Connecting redis-py to a Redis Cluster instance(s) requires at a minimum a -single node for cluster discovery. There are multiple ways in which a cluster -instance can be created: - -- Using 'host' and 'port' arguments: - -``` pycon ->>> from redis.cluster import RedisCluster as Redis ->>> rc = Redis(host='localhost', port=6379) ->>> print(rc.get_nodes()) - [[host=127.0.0.1,port=6379,name=127.0.0.1:6379,server_type=primary,redis_connection=Redis>>], [host=127.0.0.1,port=6378,name=127.0.0.1:6378,server_type=primary,redis_connection=Redis>>], [host=127.0.0.1,port=6377,name=127.0.0.1:6377,server_type=replica,redis_connection=Redis>>]] -``` -- Using the Redis URL specification: - -``` pycon ->>> from redis.cluster import RedisCluster as Redis ->>> rc = Redis.from_url("redis://localhost:6379/0") -``` - -- Directly, via the ClusterNode class: - -``` pycon ->>> from redis.cluster import RedisCluster as Redis ->>> from redis.cluster import ClusterNode ->>> nodes = [ClusterNode('localhost', 6379), ClusterNode('localhost', 6378)] ->>> rc = Redis(startup_nodes=nodes) -``` - -When a RedisCluster instance is being created it first attempts to establish a -connection to one of the provided startup nodes. If none of the startup nodes -are reachable, a 'RedisClusterException' will be thrown. -After a connection to the one of the cluster's nodes is established, the -RedisCluster instance will be initialized with 3 caches: -a slots cache which maps each of the 16384 slots to the node/s handling them, -a nodes cache that contains ClusterNode objects (name, host, port, redis connection) -for all of the cluster's nodes, and a commands cache contains all the server -supported commands that were retrieved using the Redis 'COMMAND' output. -See *RedisCluster specific options* below for more. - -RedisCluster instance can be directly used to execute Redis commands. When a -command is being executed through the cluster instance, the target node(s) will -be internally determined. When using a key-based command, the target node will -be the node that holds the key's slot. -Cluster management commands and other commands that are not key-based have a -parameter called 'target_nodes' where you can specify which nodes to execute -the command on. In the absence of target_nodes, the command will be executed -on the default cluster node. As part of cluster instance initialization, the -cluster's default node is randomly selected from the cluster's primaries, and -will be updated upon reinitialization. Using r.get_default_node(), you can -get the cluster's default node, or you can change it using the -'set_default_node' method. - -The 'target_nodes' parameter is explained in the following section, -'Specifying Target Nodes'. - -``` pycon ->>> # target-nodes: the node that holds 'foo1's key slot ->>> rc.set('foo1', 'bar1') ->>> # target-nodes: the node that holds 'foo2's key slot ->>> rc.set('foo2', 'bar2') ->>> # target-nodes: the node that holds 'foo1's key slot ->>> print(rc.get('foo1')) -b'bar' ->>> # target-node: default-node ->>> print(rc.keys()) -[b'foo1'] ->>> # target-node: default-node ->>> rc.ping() -``` - -**Specifying Target Nodes:** - -As mentioned above, all non key-based RedisCluster commands accept the kwarg -parameter 'target_nodes' that specifies the node/nodes that the command should -be executed on. -The best practice is to specify target nodes using RedisCluster class's node -flags: PRIMARIES, REPLICAS, ALL_NODES, RANDOM. When a nodes flag is passed -along with a command, it will be internally resolved to the relevant node/s. -If the nodes topology of the cluster changes during the execution of a command, -the client will be able to resolve the nodes flag again with the new topology -and attempt to retry executing the command. - -``` pycon ->>> from redis.cluster import RedisCluster as Redis ->>> # run cluster-meet command on all of the cluster's nodes ->>> rc.cluster_meet('127.0.0.1', 6379, target_nodes=Redis.ALL_NODES) ->>> # ping all replicas ->>> rc.ping(target_nodes=Redis.REPLICAS) ->>> # ping a random node ->>> rc.ping(target_nodes=Redis.RANDOM) ->>> # get the keys from all cluster nodes ->>> rc.keys(target_nodes=Redis.ALL_NODES) -[b'foo1', b'foo2'] ->>> # execute bgsave in all primaries ->>> rc.bgsave(Redis.PRIMARIES) -``` - -You could also pass ClusterNodes directly if you want to execute a command on a -specific node / node group that isn't addressed by the nodes flag. However, if -the command execution fails due to cluster topology changes, a retry attempt -will not be made, since the passed target node/s may no longer be valid, and -the relevant cluster or connection error will be returned. - -``` pycon ->>> node = rc.get_node('localhost', 6379) ->>> # Get the keys only for that specific node ->>> rc.keys(target_nodes=node) ->>> # get Redis info from a subset of primaries ->>> subset_primaries = [node for node in rc.get_primaries() if node.port > 6378] ->>> rc.info(target_nodes=subset_primaries) -``` - -In addition, the RedisCluster instance can query the Redis instance of a -specific node and execute commands on that node directly. The Redis client, -however, does not handle cluster failures and retries. - -``` pycon ->>> cluster_node = rc.get_node(host='localhost', port=6379) ->>> print(cluster_node) -[host=127.0.0.1,port=6379,name=127.0.0.1:6379,server_type=primary,redis_connection=Redis>>] ->>> r = cluster_node.redis_connection ->>> r.client_list() -[{'id': '276', 'addr': '127.0.0.1:64108', 'fd': '16', 'name': '', 'age': '0', 'idle': '0', 'flags': 'N', 'db': '0', 'sub': '0', 'psub': '0', 'multi': '-1', 'qbuf': '26', 'qbuf-free': '32742', 'argv-mem': '10', 'obl': '0', 'oll': '0', 'omem': '0', 'tot-mem': '54298', 'events': 'r', 'cmd': 'client', 'user': 'default'}] ->>> # Get the keys only for that specific node ->>> r.keys() -[b'foo1'] -``` - -**Multi-key commands:** - -Redis supports multi-key commands in Cluster Mode, such as Set type unions or -intersections, mset and mget, as long as the keys all hash to the same slot. -By using RedisCluster client, you can use the known functions (e.g. mget, mset) -to perform an atomic multi-key operation. However, you must ensure all keys are -mapped to the same slot, otherwise a RedisClusterException will be thrown. -Redis Cluster implements a concept called hash tags that can be used in order -to force certain keys to be stored in the same hash slot, see -[Keys hash tag](https://redis.io/topics/cluster-spec#keys-hash-tags). -You can also use nonatomic for some of the multikey operations, and pass keys -that aren't mapped to the same slot. The client will then map the keys to the -relevant slots, sending the commands to the slots' node owners. Non-atomic -operations batch the keys according to their hash value, and then each batch is -sent separately to the slot's owner. - -``` pycon -# Atomic operations can be used when all keys are mapped to the same slot ->>> rc.mset({'{foo}1': 'bar1', '{foo}2': 'bar2'}) ->>> rc.mget('{foo}1', '{foo}2') -[b'bar1', b'bar2'] -# Non-atomic multi-key operations splits the keys into different slots ->>> rc.mset_nonatomic({'foo': 'value1', 'bar': 'value2', 'zzz': 'value3') ->>> rc.mget_nonatomic('foo', 'bar', 'zzz') -[b'value1', b'value2', b'value3'] -``` - -**Cluster PubSub:** - -When a ClusterPubSub instance is created without specifying a node, a single -node will be transparently chosen for the pubsub connection on the -first command execution. The node will be determined by: - 1. Hashing the channel name in the request to find its keyslot - 2. Selecting a node that handles the keyslot: If read_from_replicas is - set to true, a replica can be selected. - -*Known limitations with pubsub:* - -Pattern subscribe and publish do not currently work properly due to key slots. -If we hash a pattern like fo* we will receive a keyslot for that string but -there are endless possibilities for channel names based on this pattern - -unknowable in advance. This feature is not disabled but the commands are not -currently recommended for use. -See [redis-py-cluster documentation](https://redis-py-cluster.readthedocs.io/en/stable/pubsub.html) - for more. - -``` pycon ->>> p1 = rc.pubsub() -# p1 connection will be set to the node that holds 'foo' keyslot ->>> p1.subscribe('foo') -# p2 connection will be set to node 'localhost:6379' ->>> p2 = rc.pubsub(rc.get_node('localhost', 6379)) -``` - -**Read Only Mode** - -By default, Redis Cluster always returns MOVE redirection response on accessing -a replica node. You can overcome this limitation and scale read commands by -triggering READONLY mode. - -To enable READONLY mode pass read_from_replicas=True to RedisCluster -constructor. When set to true, read commands will be assigned between the -primary and its replications in a Round-Robin manner. - -READONLY mode can be set at runtime by calling the readonly() method with -target_nodes='replicas', and read-write access can be restored by calling the -readwrite() method. - -``` pycon ->>> from cluster import RedisCluster as Redis -# Use 'debug' log level to print the node that the command is executed on ->>> rc_readonly = Redis(startup_nodes=startup_nodes, -... read_from_replicas=True) ->>> rc_readonly.set('{foo}1', 'bar1') ->>> for i in range(0, 4): -... # Assigns read command to the slot's hosts in a Round-Robin manner -... rc_readonly.get('{foo}1') -# set command would be directed only to the slot's primary node ->>> rc_readonly.set('{foo}2', 'bar2') -# reset READONLY flag ->>> rc_readonly.readwrite(target_nodes='replicas') -# now the get command would be directed only to the slot's primary node ->>> rc_readonly.get('{foo}1') -``` - -**Cluster Pipeline** - -ClusterPipeline is a subclass of RedisCluster that provides support for Redis -pipelines in cluster mode. -When calling the execute() command, all the commands are grouped by the node -on which they will be executed, and are then executed by the respective nodes -in parallel. The pipeline instance will wait for all the nodes to respond -before returning the result to the caller. Command responses are returned as a -list sorted in the same order in which they were sent. -Pipelines can be used to dramatically increase the throughput of Redis Cluster -by significantly reducing the the number of network round trips between the -client and the server. - -``` pycon ->>> with rc.pipeline() as pipe: -... pipe.set('foo', 'value1') -... pipe.set('bar', 'value2') -... pipe.get('foo') -... pipe.get('bar') -... print(pipe.execute()) -[True, True, b'value1', b'value2'] -... pipe.set('foo1', 'bar1').get('foo1').execute() -[True, b'bar1'] -``` - -Please note: -- RedisCluster pipelines currently only support key-based commands. -- The pipeline gets its 'read_from_replicas' value from the cluster's parameter. -Thus, if read from replications is enabled in the cluster instance, the pipeline -will also direct read commands to replicas. -- The 'transaction' option is NOT supported in cluster-mode. In non-cluster mode, -the 'transaction' option is available when executing pipelines. This wraps the -pipeline commands with MULTI/EXEC commands, and effectively turns the pipeline -commands into a single transaction block. This means that all commands are -executed sequentially without any interruptions from other clients. However, -in cluster-mode this is not possible, because commands are partitioned -according to their respective destination nodes. This means that we can not -turn the pipeline commands into one transaction block, because in most cases -they are split up into several smaller pipelines. - -**Lua Scripting in Cluster Mode** - -Cluster mode has limited support for lua scripting. - -The following commands are supported, with caveats: -- `EVAL` and `EVALSHA`: The command is sent to the relevant node, depending on -the keys (i.e., in `EVAL "