Redix (Redix v1.1.3) View Source

This module provides the main API to interface with Redis.

Overview

start_link/2 starts a process that connects to Redis. Each Elixir process started with this function maps to a client TCP connection to the specified Redis server.

The architecture is very simple: when you issue commands to Redis (via command/3 or pipeline/3), the Redix process sends the command to Redis right away and is immediately able to send new commands. When a response arrives from Redis, only then the Redix process replies to the caller with the response. This pattern avoids blocking the Redix process for each request (until a response arrives), increasing the performance of this driver.

Reconnections

Redix tries to be as resilient as possible: it tries to recover automatically from most network errors.

If there's a network error when sending data to Redis or if the connection to Redis drops, Redix tries to reconnect. The first reconnection attempt will happen after a fixed time interval; if this attempt fails, reconnections are attempted until successful, and the time interval between reconnections is increased exponentially. Some aspects of this behaviour can be configured; see start_link/2 and the "Reconnections" page in the docs for more information.

Sentinel

Note: support for Redis Sentinel is still experimental. It works, but the API might change a little bit and the design might be revisited.

Redix supports Redis Sentinel by passing a :sentinel option to start_link/1 (or start_link/2) instead of :host and :port. In :sentinel, you'll specify a list of sentinel nodes to try when connecting and the name of a primary group (see start_link/1 for more detailed information on these options). When connecting, Redix will attempt to connect to each of the specified sentinels in the given order. When it manages to connect to a sentinel, it will ask that sentinel for the address of the primary for the given primary group. Then, it will connect to that primary and ask it for confirmation that it is indeed a primary. If anything in this process doesn't go right, the next sentinel in the list will be tried.

All of this happens in case of disconnections as well. If there's a disconnection, the whole process of asking sentinels for a primary is executed again.

You should only care about Redis Sentinel when starting a Redix connection: once started, using the connection will be exactly the same as the non-sentinel scenario.

Transactions or pipelining?

Pipelining and transactions have things in common but they're fundamentally different. With a pipeline, you're sending all commands in the pipeline at once on the connection to Redis. This means Redis receives all commands at once, but the Redis server is not guaranteed to process all those commands at once.

On the other hand, a MULTI/EXEC transaction guarantees that when EXEC is called all the queued commands in the transaction are executed atomically. However, you don't need to send all the commands in the transaction at once. If you want to combine pipelining with MULTI/EXEC transactions, use transaction_pipeline/3.

Skipping replies

Redis provides commands to control whether you want replies to your commands or not. These commands are CLIENT REPLY ON, CLIENT REPLY SKIP, and CLIENT REPLY OFF. When you use CLIENT REPLY SKIP, only the command that follows will not get a reply. When you use CLIENT REPLY OFF, all the commands that follow will not get replies until CLIENT REPLY ON is issued. Redix does not support these commands directly because they would change the whole state of the connection. To skip replies, use noreply_pipeline/3 or noreply_command/3.

Skipping replies is useful to improve performance when you want to issue many commands but are not interested in the responses to those commands.

SSL

Redix supports SSL by passing ssl: true in start_link/1. You can use the :socket_opts option to pass options that will be used by the SSL socket, like certificates.

If the CAStore dependency is available, Redix will pick up its CA certificate store file automatically. You can select a different CA certificate store by passing in the :cacertfile or :cacerts socket options. If the server uses a self-signed certificate, such as for testing purposes, disable certificate verification by passing verify: :verify_none in the socket options.

Some Redis servers, notably Amazon ElastiCache, use wildcard certificates that require additional socket options for successful verification (requires OTP 21.0 or later):

Redix.start_link(
  host: "example.com", port: 9999, ssl: true,
  socket_opts: [
    customize_hostname_check: [
      match_fun: :public_key.pkix_verify_hostname_match_fun(:https)
    ]
  ]
)

Telemetry

Redix uses Telemetry for instrumentation and logging. See Redix.Telemetry.

Link to this section Summary

Functions

Returns a child spec to use Redix in supervision trees.

Issues a command on the Redis server.

Issues a command on the Redis server, raising if there's an error.

Same as command/3 but tells the Redis server to not return a response.

Same as noreply_command/3 but raises in case of errors.

Issues a pipeline of commands to the Redis server, asking the server to not send responses.

Issues a pipeline of commands on the Redis server.

Issues a pipeline of commands to the Redis server, raising if there's an error.

Starts a connection to Redis.

Starts a connection to Redis.

Closes the connection to the Redis server.

Executes a MULTI/EXEC transaction.

Executes a MULTI/EXEC transaction.

Link to this section Types

Specs

command() :: [String.Chars.t()]

Specs

connection() :: GenServer.server()

Link to this section Functions

Specs

child_spec(uri | keyword() | {uri, keyword()}) :: Supervisor.child_spec()
when uri: binary()

Returns a child spec to use Redix in supervision trees.

To use Redix with the default options (same as calling Redix.start_link()):

children = [
  Redix,
  # ...
]

You can pass options:

children = [
  {Redix, host: "redix.example.com", name: :redix},
  # ...
]

You can also pass a URI:

children = [
  {Redix, "redis://redix.example.com:6380"}
]

If you want to pass both a URI and options, you can do it by passing a tuple with the URI as the first element and the list of options (make sure it has brackets around if using literals) as the second element:

children = [
  {Redix, {"redis://redix.example.com", [name: :redix]}}
]
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command(conn, command, opts \\ [])

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Specs

Issues a command on the Redis server.

This function sends command to the Redis server and returns the response returned by Redis. pid must be the pid of a Redix connection. command must be a list of strings making up the Redis command and its arguments.

The return value is {:ok, response} if the request is successful and the response is not a Redis error. {:error, reason} is returned in case there's an error in the request (such as losing the connection to Redis in between the request). reason can also be a Redix.Error exception in case Redis is reachable but returns an error (such as a type error).

If the given command is an empty command ([]), an ArgumentError exception is raised.

This function accepts the same options as pipeline/3.

Examples

iex> Redix.command(conn, ["SET", "mykey", "foo"])
{:ok, "OK"}
iex> Redix.command(conn, ["GET", "mykey"])
{:ok, "foo"}

iex> Redix.command(conn, ["INCR", "mykey"])
{:error, "ERR value is not an integer or out of range"}

If Redis goes down (before a reconnection happens):

iex> {:error, error} = Redix.command(conn, ["GET", "mykey"])
iex> error.reason
:closed
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command!(conn, command, opts \\ [])

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Specs

Issues a command on the Redis server, raising if there's an error.

This function works exactly like command/3 but:

  • if the command is successful, then the result is returned directly (not wrapped in a {:ok, result} tuple).
  • if there's a Redis error or a connection error, a Redix.Error or Redix.ConnectionError error is raised.

This function accepts the same options as command/3.

Examples

iex> Redix.command!(conn, ["SET", "mykey", "foo"])
"OK"

iex> Redix.command!(conn, ["INCR", "mykey"])
** (Redix.Error) ERR value is not an integer or out of range

If Redis goes down (before a reconnection happens):

iex> Redix.command!(conn, ["GET", "mykey"])
** (Redix.ConnectionError) :closed
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noreply_command(conn, command, opts \\ [])

View Source (since 0.8.0)

Specs

noreply_command(connection(), command(), keyword()) ::
  :ok | {:error, atom() | Redix.Error.t() | Redix.ConnectionError.t()}

Same as command/3 but tells the Redis server to not return a response.

This function is useful when you want to send a command but you don't care about the response. Since the response is not returned, the return value of this function in case the command is successfully sent to Redis is :ok.

Not receiving a response means saving traffic on the network and memory allocation for the response. See also noreply_pipeline/3.

This function accepts the same options as pipeline/3.

Examples

iex> Redix.noreply_command(conn, ["INCR", "mykey"])
:ok
iex> Redix.command(conn, ["GET", "mykey"])
{:ok, "1"}
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noreply_command!(conn, command, opts \\ [])

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Specs

noreply_command!(connection(), command(), keyword()) :: :ok

Same as noreply_command/3 but raises in case of errors.

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noreply_pipeline(conn, commands, opts \\ [])

View Source (since 0.8.0)

Specs

noreply_pipeline(connection(), [command()], keyword()) ::
  :ok | {:error, atom() | Redix.Error.t() | Redix.ConnectionError.t()}

Issues a pipeline of commands to the Redis server, asking the server to not send responses.

This function is useful when you want to issue commands to the Redis server but you don't care about the responses. For example, you might want to set a bunch of keys but you don't care for a confirmation that they were set. In these cases, you can save bandwidth by asking Redis to not send replies to your commands.

Since no replies are sent back, this function returns :ok in case there are no network errors, or {:error, reason} otherwise.any()

This function accepts the same options as pipeline/3.

Examples

iex> commands = [["INCR", "mykey"], ["INCR", "meykey"]]
iex> Redix.noreply_pipeline(conn, commands)
:ok
iex> Redix.command(conn, ["GET", "mykey"])
{:ok, "2"}
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noreply_pipeline!(conn, commands, opts \\ [])

View Source (since 0.8.0)

Specs

noreply_pipeline!(connection(), [command()], keyword()) :: :ok

Same as noreply_pipeline/3 but raises in case of errors.

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pipeline(conn, commands, opts \\ [])

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Specs

pipeline(connection(), [command()], keyword()) ::
  {:ok, [Redix.Protocol.redis_value()]}
  | {:error, atom() | Redix.Error.t() | Redix.ConnectionError.t()}

Issues a pipeline of commands on the Redis server.

commands must be a list of commands, where each command is a list of strings making up the command and its arguments. The commands will be sent as a single "block" to Redis, and a list of ordered responses (one for each command) will be returned.

The return value is {:ok, results} if the request is successful, {:error, reason} otherwise.

Note that {:ok, results} is returned even if results contains one or more Redis errors (Redix.Error structs). This is done to avoid having to walk the list of results (a O(n) operation) to look for errors, leaving the responsibility to the user. That said, errors other than Redis errors (like network errors) always cause the return value to be {:error, reason}.

If commands is an empty list ([]) or any of the commands in commands is an empty command ([]) then an ArgumentError exception is raised right away.

Pipelining is not the same as a transaction. For more information, see the module documentation.

Options

  • :timeout - (integer or :infinity) request timeout (in milliseconds). Defaults to 5000. If the Redis server doesn't reply within this timeout, {:error, %Redix.ConnectionError{reason: :timeout}} is returned.

Examples

iex> Redix.pipeline(conn, [["INCR", "mykey"], ["INCR", "mykey"], ["DECR", "mykey"]])
{:ok, [1, 2, 1]}

iex> Redix.pipeline(conn, [["SET", "k", "foo"], ["INCR", "k"], ["GET", "k"]])
{:ok, ["OK", %Redix.Error{message: "ERR value is not an integer or out of range"}, "foo"]}

If Redis goes down (before a reconnection happens):

iex> {:error, error} = Redix.pipeline(conn, [["SET", "mykey", "foo"], ["GET", "mykey"]])
iex> error.reason
:closed
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pipeline!(conn, commands, opts \\ [])

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Specs

pipeline!(connection(), [command()], keyword()) :: [
  Redix.Protocol.redis_value()
]

Issues a pipeline of commands to the Redis server, raising if there's an error.

This function works similarly to pipeline/3, except:

  • if there are no errors in issuing the commands (even if there are one or more Redis errors in the results), the results are returned directly (not wrapped in a {:ok, results} tuple).
  • if there's a connection error then a Redix.ConnectionError exception is raised.

For more information on why nothing is raised if there are one or more Redis errors (Redix.Error structs) in the list of results, look at the documentation for pipeline/3.

This function accepts the same options as pipeline/3.

Examples

iex> Redix.pipeline!(conn, [["INCR", "mykey"], ["INCR", "mykey"], ["DECR", "mykey"]])
[1, 2, 1]

iex> Redix.pipeline!(conn, [["SET", "k", "foo"], ["INCR", "k"], ["GET", "k"]])
["OK", %Redix.Error{message: "ERR value is not an integer or out of range"}, "foo"]

If Redis goes down (before a reconnection happens):

iex> Redix.pipeline!(conn, [["SET", "mykey", "foo"], ["GET", "mykey"]])
** (Redix.ConnectionError) :closed
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start_link(uri_or_opts \\ [])

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Specs

start_link(binary() | keyword()) :: :gen_statem.start_ret()

Starts a connection to Redis.

This function returns {:ok, pid} if the Redix process is started successfully.

{:ok, pid} = Redix.start_link()

The actual TCP connection to the Redis server may happen either synchronously, before start_link/2 returns, or asynchronously. This behaviour is decided by the :sync_connect option (see below).

This function accepts one argument which can either be an string representing a URI or a keyword list of options.

Using in supervision trees

Redix supports child specs, so you can use it as part of a supervision tree:

children = [
  {Redix, host: "redix.myapp.com", name: :redix}
]

See child_spec/1 for more information.

Using a Redis URI

In case uri_or_opts is a Redis URI, it must be in the form:

redis://[username:password@]host[:port][/db]

Here are some examples of valid URIs:

  • redis://localhost
  • redis://:secret@localhost:6397
  • redis://username:secret@localhost:6397
  • redis://example.com:6380/1

The only mandatory thing when using URIs is the host. All other elements are optional and their default value can be found in the "Options" section below.

In earlier versions of Redix, the username in the URI was ignored. Redis 6 introduced ACL support. Now, Redix supports usernames as well.

Options

Redis options

The following options can be used to specify the parameters used to connect to Redis (instead of a URI as described above):

  • :host - (string) the host where the Redis server is running. Defaults to "localhost".

  • :port - (positive integer) the port on which the Redis server is running. Defaults to 6379.

  • :username - (string) the username to connect to Redis. Defaults to nil, meaning no username is used. Redis supports usernames only since Redis 6 (see the ACL documentation). If a username is provided (either via options or via URIs) and the Redis version used doesn't support ACL, then Redix falls back to using just the password and emits a warning. In future Redix versions, Redix will raise if a username is passed and the Redis version used doesn't support ACL.

  • :password - (string or MFA) the password used to connect to Redis. Defaults to nil, meaning no password is used. When this option is provided, all Redix does is issue an AUTH command to Redis in order to authenticate. MFAs are also supported in the form of {module, function, arguments}. This can be used to fetch the password dynamically on every reconnection but most importantly to hide the password from crash reports in case the Redix connection crashes for any reason. For example, you can use password: {System, :fetch_env!, ["REDIX_PASSWORD"]}.

  • :database - (non-negative integer or string) the database to connect to. Defaults to nil, meaning Redix doesn't connect to a specific database (the default in this case is database 0). When this option is provided, all Redix does is issue a SELECT command to Redis in order to select the given database.

Connection options

The following options can be used to tweak how the Redix connection behaves.

  • :socket_opts - (list of options) this option specifies a list of options that are passed to the network layer when connecting to the Redis server. Some socket options (like :active or :binary) will be overridden by Redix so that it functions properly.

    Defaults to [] for TCP and [verify: :verify_peer, depth: 3] for SSL. If the CAStore dependency is available, the cacertfile option is added to the SSL options by default as well.

  • :timeout - (integer) connection timeout (in milliseconds) also directly passed to the network layer. Defaults to 5000.

  • :sync_connect - (boolean) decides whether Redix should initiate the TCP connection to the Redis server before or after returning from start_link/1. This option also changes some reconnection semantics; read the "Reconnections" page in the docs.

  • :exit_on_disconnection - (boolean) if true, the Redix server will exit if it fails to connect or disconnects from Redis. Note that setting this option to true means that the :backoff_initial and :backoff_max options will be ignored. Defaults to false.

  • :backoff_initial - (non-negative integer) the initial backoff time (in milliseconds), which is the time that the Redix process will wait before attempting to reconnect to Redis after a disconnection or failed first connection. See the "Reconnections" page in the docs for more information.

  • :backoff_max - (positive integer) the maximum length (in milliseconds) of the time interval used between reconnection attempts. See the "Reconnections" page in the docs for more information.

  • :name - Redix is bound to the same registration rules as a GenServer. See the GenServer documentation for more information.

  • :ssl - (boolean) if true, connect through SSL, otherwise through TCP. The :socket_opts option applies to both SSL and TCP, so it can be used for things like certificates. See :ssl.connect/4. Defaults to false.

  • :sentinel - (keyword list) options for using Redis Sentinel. If this option is provided, then the :host and :port option cannot be provided. For the available sentinel options, see the "Sentinel options" section below.

  • :hibernate_after - (integer) if present, the Redix connection process awaits any message for the given number of milliseconds and if no message is received, the process goes into hibernation automatically (by calling :proc_lib.hibernate/3). See :gen_statem.start_opt/0. Not present by default.

  • :spawn_opt - (options) if present, its value is passed as options to the Redix connection process as in Process.spawn/4. See :gen_statem.start_opt/0. Not present by default.

  • :debug - (options) if present, the corresponding function in the :sys module is invoked. Not present by default.

Sentinel options

The following options can be used to configure the Redis Sentinel behaviour when connecting. These options should be passed in the :sentinel key in the connection options. For more information on support for Redis sentinel, see the Redix module documentation.

  • :sentinels - (list) a list of sentinel addresses. Each element in this list is the address of a sentinel to be contacted in order to obtain the address of a primary. The address of a sentinel can be passed as a Redis URI (see the "Using a Redis URI" section above) or a keyword list with :host, :port, :password options (same as when connecting to a Redis instance directly). Note that the password can either be passed in the sentinel address or globally -- see the :password option below. This option is required.

  • :group - (binary) the name of the group that identifies the primary in the sentinel configuration. This option is required.

  • :role - (:primary or :replica) if :primary, the connection will be established with the primary for the given group. If :replica, Redix will ask the sentinel for all the available replicas for the given group and try to connect to one of them at random. Defaults to :primary.

  • :socket_opts - (list of options) the socket options that will be used when connecting to the sentinels. Defaults to [].

  • :ssl - (boolean) if true, connect to the sentinels via through SSL, otherwise through TCP. The :socket_opts applies to both TCP and SSL, so it can be used for things like certificates. See :ssl.connect/4. Defaults to false.

  • :timeout - (timeout) the timeout (in milliseconds or :infinity) that will be used to interact with the sentinels. This timeout will be used as the timeout when connecting to each sentinel and when asking sentinels for a primary. The Redis documentation suggests to keep this timeout short so that connection to Redis can happen quickly.

  • :password - (string) if you don't want to specify a password for each sentinel you list, you can use this option to specify a password that will be used to authenticate on sentinels if they don't specify a password. This option is recommended over passing a password for each sentinel because in the future we might do sentinel auto-discovery, which means authentication can only be done through a global password that works for all sentinels.

Examples

iex> Redix.start_link()
{:ok, #PID<...>}

iex> Redix.start_link(host: "example.com", port: 9999, password: "secret")
{:ok, #PID<...>}

iex> Redix.start_link(database: 3, name: :redix_3)
{:ok, #PID<...>}
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start_link(uri, other_opts)

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Specs

start_link(binary(), keyword()) :: :gen_statem.start_ret()

Starts a connection to Redis.

This is the same as start_link/1, but the URI and the options get merged. other_opts have precedence over the things specified in uri. Take this code:

Redix.start_link("redis://localhost:6379", port: 6380)

In this example, port 6380 will be used.

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stop(conn, timeout \\ :infinity)

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Specs

stop(connection(), timeout()) :: :ok

Closes the connection to the Redis server.

This function is synchronous and blocks until the given Redix connection frees all its resources and disconnects from the Redis server. timeout can be passed to limit the amount of time allowed for the connection to exit; if it doesn't exit in the given interval, this call exits.

Examples

iex> Redix.stop(conn)
:ok
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transaction_pipeline(conn, commands, options \\ [])

View Source (since 0.8.0)

Specs

transaction_pipeline(connection(), [command()], keyword()) ::
  {:ok, [Redix.Protocol.redis_value()]}
  | {:error, atom() | Redix.Error.t() | Redix.ConnectionError.t()}

Executes a MULTI/EXEC transaction.

Redis supports something akin to transactions. It works by sending a MULTI command, then some commands, and then an EXEC command. All the commands after MULTI are queued until EXEC is issued. When EXEC is issued, all the responses to the queued commands are returned in a list.

This function accepts the same options as pipeline/3.

Examples

To run a MULTI/EXEC transaction in one go, use this function and pass a list of commands to use in the transaction:

iex> Redix.transaction_pipeline(conn, [["SET", "mykey", "foo"], ["GET", "mykey"]])
{:ok, ["OK", "foo"]}

Problems with transactions

There's an inherent problem with Redix's architecture and MULTI/EXEC transaction. A Redix process is a single connection to Redis that can be used by many clients. If a client A sends MULTI and client B sends a command before client A sends EXEC, client B's command will be part of the transaction. This is intended behaviour, but it might not be what you expect. This is why transaction_pipeline/3 exists: this function wraps commands in MULTI/EXEC but sends all in a pipeline. Since everything is sent in the pipeline, it's sent at once on the connection and no commands can end up in the middle of the transaction.

Running MULTI/EXEC transactions manually

There are still some cases where you might want to start a transaction with MULTI, then send commands from different processes that you actively want to be in the transaction, and then send an EXEC to run the transaction. It's still fine to do this with command/3 or pipeline/3, but remember what explained in the section above. If you do this, do it in an isolated connection (open a new one if necessary) to avoid mixing things up.

Link to this function

transaction_pipeline!(conn, commands, options \\ [])

View Source (since 0.8.0)

Specs

transaction_pipeline!(connection(), [command()], keyword()) :: [
  Redix.Protocol.redis_value()
]

Executes a MULTI/EXEC transaction.

Same as transaction_pipeline/3, but returns the result directly instead of wrapping it in an {:ok, result} tuple or raises if there's an error.

This function accepts the same options as pipeline/3.

Examples

iex> Redix.transaction_pipeline!(conn, [["SET", "mykey", "foo"], ["GET", "mykey"]])
["OK", "foo"]