Redis.Cache.Backend behaviour (Redis v0.7.1)

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Behaviour for pluggable client-side cache backends.

The default implementation is Redis.Cache.Store, which uses ETS tables with bounded size, LRU/FIFO eviction, and TTL support.

Implement this behaviour to use an alternative cache backend (e.g., Cachex, ConCache, or a custom store).

Example

defmodule MyApp.CachexBackend do
  @behaviour Redis.Cache.Backend

  @impl true
  def init(opts) do
    name = Keyword.get(opts, :name, :my_cache)
    {:ok, _pid} = Cachex.start_link(name)
    {:ok, %{name: name}}
  end

  @impl true
  def get(state, key) do
    case Cachex.get(state.name, key) do
      {:ok, nil} -> {:miss, state}
      {:ok, value} -> {:hit, value, state}
    end
  end

  # ... implement remaining callbacks
end

Then pass it when starting the cache:

Redis.Cache.start_link(
  port: 6379,
  backend: MyApp.CachexBackend,
  backend_opts: [name: :my_redis_cache]
)

Summary

Types

state()

Callbacks

destroy(state)

Destroys the cache backend and releases resources.

flush(state)

Clears the entire cache.

get(state, key)

Gets a value from the cache.

init(opts)

Initializes the backend. Returns {:ok, state} or {:error, reason}.

invalidate(state, keys)

Invalidates one or more keys directly.

invalidate_refs(state, keys)

Invalidates all cache entries that reference the given Redis key(s).

put(state, key, value, ttl_ms)

Puts a value in the cache with optional TTL in milliseconds.

put_with_ref(state, cache_key, redis_key, value, ttl_ms)

Puts a value and records a ref from redis_key to cache_key.

stats(state)

Returns cache statistics as a map.

sweep_expired(state)

Removes expired entries from the cache.

Types

state()

@type state() :: term()

Callbacks

destroy(state)

@callback destroy(state()) :: :ok

Destroys the cache backend and releases resources.

flush(state)

@callback flush(state()) :: state()

Clears the entire cache.

get(state, key)

@callback get(state(), key :: term()) ::
  {:hit, value :: term(), state()} | {:miss, state()}

Gets a value from the cache.

Returns {:hit, value, state} on cache hit or {:miss, state} on miss.

init(opts)

@callback init(opts :: keyword()) :: {:ok, state()} | {:error, term()}

Initializes the backend. Returns {:ok, state} or {:error, reason}.

invalidate(state, keys)

@callback invalidate(state(), keys :: [String.t()] | nil) :: state()

Invalidates one or more keys directly.

Called when Redis pushes invalidation. A nil keys argument means flush all entries.

invalidate_refs(state, keys)

@callback invalidate_refs(state(), keys :: [String.t()] | nil) :: state()

Invalidates all cache entries that reference the given Redis key(s).

Called when Redis pushes invalidation for keys that were cached via put_with_ref/5. A nil keys argument is a no-op.

put(state, key, value, ttl_ms)

@callback put(state(), key :: term(), value :: term(), ttl_ms :: non_neg_integer() | nil) ::
  state()

Puts a value in the cache with optional TTL in milliseconds.

put_with_ref(state, cache_key, redis_key, value, ttl_ms)

@callback put_with_ref(
  state(),
  cache_key :: term(),
  redis_key :: String.t(),
  value :: term(),
  ttl_ms :: non_neg_integer() | nil
) :: state()

Puts a value and records a ref from redis_key to cache_key.

When redis_key is later invalidated via invalidate_refs/2, all cache entries that reference it should be removed.

stats(state)

@callback stats(state()) :: map()

Returns cache statistics as a map.

sweep_expired(state)

@callback sweep_expired(state()) :: state()

Removes expired entries from the cache.