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Elixir Library: Redis Distributed Lock implementation
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README.md

Redlock

This library is an implementation of Redlock (Redis destributed lock)

Redlock

Installation

If available in Hex, the package can be installed by adding redlock to your list of dependencies in mix.exs:

def deps do
  [
    {:redlock, "~> 1.0.10"}
  ]
end

Documentation can be generated with ExDoc and published on HexDocs. Once published, the docs can be found at https://hexdocs.pm/redlock.

Usage

resource = "example_key:#{user_id}"
lock_exp_sec = 10

case Redlock.lock(resource, lock_exp_sec) do

  {:ok, mutex} ->
    # some other code which write and read on RDBMS, KVS or other storage
    # call unlock finally
    Redlock.unlock(resource, mutex)

  :error ->
    Logger.error "failed to lock resource. maybe redis connection got trouble."
    {:error, :system_error}

end

Or you can use transaction function

def my_function() do
  # do something, and return {:ok, :my_result} or {:error, :my_error}
end

def execute_with_lock() do

  resource = "example_key:#{user_id}"
  lock_exp_sec = 10

  case Redlock.transaction(resource, lock_exp_sec, &my_function/0) do

    {:ok, :my_result} ->
      Logger.info "this is the return-value of my_function/0"
      :ok

    {:error, :my_error} ->
      Logger.info "this is the return-value of my_function/0"
      :error

    {:error, :lock_failure} ->
      Logger.info "if locking has failed, Redlock returns this error"
      :error

  end
end

Setup

children = [
  # other workers/supervisors

  {Redlock, [pool_size: 2, ...]}
]
Supervisor.start_link(children, strategy: :one_for_one)

Options

Single Node Mode

readlock_opts = [

  pool_size:                  2,
  drift_factor:               0.01,
  max_retry:                  3,
  retry_interval_base:        300,
  retry_interval_max:         3_000,
  reconnection_interval_base: 500,
  reconnection_interval_max:  5_000,

  # you must set odd number of server
  servers: [
    [host: "redis1.example.com", port: 6379],
    [host: "redis2.example.com", port: 6379],
    [host: "redis3.example.com", port: 6379]
  ]

]
  • pool_size: pool_size of number of connection pool for each Redis master node, default is 2
  • drift_factor: number used for calculating validity for results, see https://redis.io/topics/distlock for more detail.
  • max_retry: how many times you want to retry if you failed to lock resource.
  • retry_interval_max: (milliseconds) used to decide how long you want to wait untill your next try after a lock-failure.
  • retry_interval_base: (milliseconds) used to decide how long you want to wait untill your next try after a lock-failure.
  • reconnection_interval_base: (milliseconds) used to decide how long you want to wait until your next try after a redis-disconnection
  • reconnection_interval_max: (milliseconds) used to decide how long you want to wait until your next try after a redis-disconnection
  • servers: host, port and auth settings for each redis-server. this amount must be odd. Auth can be omitted if no authentication is reaquired

How long you want to wait until your next try after a redis-disconnection or lock-failure

the interval(milliseconds) is decided by following calculation.

min(XXX_interval_max, (XXX_interval_base * (attempts_count ** 2)))

Cluster Mode

readlock_opts = [

  pool_size:                  2,
  drift_factor:               0.01,
  max_retry:                  3,
  retry_interval_base:        300,
  retry_interval_max:         3_000,
  reconnection_interval_base: 500,
  reconnection_interval_max:  5_000,

  cluster: [
    # first node
    [
      # you must set odd number of server
      [host: "redis1.example.com", port: 6379, auth: password],
      [host: "redis2.example.com", port: 6379, auth: password],
      [host: "redis3.example.com", port: 6379, auth: password]
    ],
    # second node
    [
      # you must set odd number of server
      [host: "redis4.example.com", port: 6379],
      [host: "redis5.example.com", port: 6379],
      [host: "redis6.example.com", port: 6379]
    ],
    # third node
    [
      # you must set odd number of server
      [host: "redis7.example.com", port: 6379],
      [host: "redis8.example.com", port: 6379],
      [host: "redis9.example.com", port: 6379]
    ]
  ]

]

Set cluster option instead of servers, then Redlock works as cluster mode. When you want to lock some resource, Redlock chooses a node depends on a resource key with consistent-hashing way (ketama algorithm using md5).

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