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Redis

A fully-featured Redis client for the Julia programming language

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Redis.jl

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Redis.jl is a fully-featured Redis client for the Julia programming language. The implementation is an attempt at an easy to understand, minimalistic API that mirrors actual Redis commands as closely as possible.

Basics

The Redis.jl API resides in the Redis module.

using Redis

The main entrypoint into the API is the RedisConnection, which represents a stateful TCP connection to a single Redis server instance. A single constructor allows the user to set all parameters while supplying the usual Redis defaults. Once a RedisConnection has been created, it can be used to access any of the expected Redis commands.

conn = RedisConnection() # host=127.0.0.1, port=6379, db=0, no password
# conn = RedisConnection(host="192.168.0.1", port=6380, db=15, password="supersecure")

set(conn, "foo", "bar")
get(conn, "foo") # Returns "bar"

Anywhere that String would normally be accepted, keywords can be passed as well. In fact, any Type can be passed so long as the type has a method for the string function.

set(conn, :keyword, :value)
get(conn, :keyword) # Returns "value"

For any Redis command x, the Julia function to call that command is x. Redis commands with spaces in them have their spaces replaced with underscores (_). For those already familiar with available Redis commands, this convention should make the API relatively straightforward to understand. There are two exceptions to this convention due to conflicts with Julia:

  • The type key command is keytype
  • The eval scripting command is evalscript

When the user is finished interacting with Redis, the connection should be destroyed to prevent resource leaks:

disconnect(conn)

The disconnect function can be used with any of the connection types detailed below.

Commands with options

Some Redis commands have a more complex syntax that allows for options to be passed to the command. Redis.jl supports these options through the use of a final varargs parameter to those functions (for example, scan). In these cases, the options should be passed as individual strings at the end of the function. As mentioned earlier, keywords or other Types can be passed for these options as well and will be coerced to String.

scan(conn, 0, "match", "foo*")
scan(conn, 2, :count, 2)

If users are interested, the API could be improved to provide custom functions for these complex commands.

An exception to this option syntax are the functions zinterstore and zunionstore, which have specific implementations to allow for ease of use due to their greater complexity.

Pipelining

Redis.jl supports pipelining through the PipelineConnection. Commands are executed in much the same way as standard Redis commands:

pipeline = open_pipeline(conn)
set(pipeline, "somekey", "somevalue")

Commands will be sent directly to the Redis server without waiting for a response. Responses can be read at any time in the future using the read_pipeline command:

responses = read_pipeline(pipeline) # responses == ["OK"]

Important: The current PipelineConnection implementation is not threadsafe. If multiple threads require access to Redis pipelines, a separate PipelineConnection should be created for each thread. This limitation could be addressed in a future commit if there is a need.

Transactions

Redis.jl supports MULTI/EXEC transactions through two methods: using a RedisConnection directly or using a specialized TransactionConnection derived from a parent connection.

Transactions using the RedisConnection

If the user wants to build a transaction a single time and execute it on the server, the simplest way to do so is to send the commands as you would at the Redis cli.

multi(conn)
set(conn, "foo", "bar")
get(conn, "foo") # Returns "QUEUED"
exec(conn) # Returns ["OK", "bar"]
get(conn, "foo") # Returns "bar"

It is important to note that after the final call to exec, the RedisConnection is returned to a 'normal' state.

Transactions using the TransactionConnection

If the user is planning on using multiple transactions on the same connection, it may make sense for the user to keep a separate connection for transactional use. The TransactionConnection is almost identical to the RedisConnection, except that it is always in a MULTI block. The user should never manually call multi with a TransactionConnection.

trans = open_transaction(conn)
set(trans, "foo", "bar")
get(trans, "foo") # Returns "QUEUED"
exec(trans) # Returns ["OK", "bar"]
get(trans, "foo") # Returns "QUEUED"
multi(trans) # Throws a ServerException

Notice the subtle difference from the previous example; after calling exec, the TransactionConnection is placed into another MULTI block rather than returning to a 'normal' state as the RedisConnection does.

Pub/sub

Redis.jl provides full support for Redis pub/sub. Publishing is accomplished by using the command as normal:

publish(conn, "channel", "hello, world!")

Subscriptions are handled using the SubscriptionConnection. Similar to the TransactionConnection, the SubscriptionConnection is constructed from an existing RedisConnection. Once created, the SubscriptionConnection maintains a simple event loop that will call the user's defined function whenever a message is received on the specified channel.

x = Any[]
f(y) = push!(x, y)
sub = open_subscription(conn)
subscribe(sub, "baz", f)
publish(conn, "baz", "foobar")
x # Returns ["foobar"]

Multiple channels can be subscribed together by providing a Dict{String, Function}.

x = Any[]
f(y) = push!(x, y)
sub = open_subscription(conn)
d = Dict{String, Function}({"baz" => f, "bar" => println})
subscribe(sub, d)
publish(conn, "baz", "foobar")
x # Returns ["foobar"]
publish(conn, "bar", "anything") # "anything" written to stdout

Pattern subscription works in the same way through use of the psubscribe function. Channels can be unsubscribed through unsubscribe and punsubscribe.

Note that the async event loop currently runs until the SubscriptionConnection is disconnected, regardless of how many subscriptions the client has active. Event loop error handling should be improved in an update to the API.

Subscription error handling

When a SubscriptionConnection instance is created via open_subscription, it spawns a routine that runs in the background to process events received from the server. In the case that Redis.jl encounters an error within this loop, the default behavior is to disregard the error and continue on. If the user would like finer control over this error handling, open_subscription accepts an optional Function parameter as its final argument. If this is provided, Redis.jl will call the provided function passing it the caught Exception as its only parameter.

Sentinel

Redis.jl also provides functionality for interacting with Redis Sentinel instances through the SentinelConnection. All Sentinel functionality other than ping is implemented through the sentinel_ functions:

sentinel = SentinelConnection() # Constructor has the same options as RedisConnection
sentinel_masters(sentinel) # Returns an Array{Dict{String, String}} of master info

SentinelConnection is also SubscribableConnection, allowing the user to build a SubscriptionConnection for monitoring cluster health through Sentinel messages. See the Redis Sentinel documentation for more information.

Notes

Actual API usage can be found in test/redis_tests.jl.

Redis Commands returning 'NIL'

The following methods return a Nullable{T}(value) corresponding to a Redis 'NIL'.

Strings

  • get(conn, "non_existent_key")
  • mget(conn, "non_existent_key1", "non_existent_key2", "non_existent_key3")

Lists

  • lindex(conn, "non_existent_list", 1)
  • lindex(conn, "one_element_list", 2)
  • lpop(conn, "non_existent_list")
  • rpop(conn, "non_existent_list")
  • rpoplpush(conn, "non_existent_list", "some_list")

Sets

  • spop(conn, "empty_set")
  • srandmember(conn, "empty_set")

Sorted Sets

  • zrank(conn, "ordered_set", "non_existent_member")
  • zrevrank(conn, "ordered_set", "non_existent_member")
  • zscore(conn, "ordered_set", "non_existent_member")

Hashes

  • hget(conn, "some_hash", "non_existent_field")
  • hmget(conn, "some_hash", "nofield1", "nofield2") html julia-observer-html-cut-paste-13__work

First Commit

11/30/2014

Last Touched

about 2 months ago

Commits

56 commits

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