Cache

The cache module provides flexible caching with multiple backend support.

Cache Stores

MemoryStore

In-process memory cache.

Azu.configure do |config|
  config.cache = Azu::Cache::MemoryStore.new
end

Options:

• max_size : Int32 - Maximum entries (default: 10000)

• default_ttl : Time::Span - Default expiration (default: 1.hour)

RedisStore

Redis-backed distributed cache.

Azu.configure do |config|
  config.cache = Azu::Cache::RedisStore.new(
    url: ENV["REDIS_URL"]
  )
end

Options:

• url : String - Redis connection URL

• pool_size : Int32 - Connection pool size

• namespace : String? - Key prefix

• default_ttl : Time::Span - Default expiration

Cache Methods

set

Store a value.

Azu.cache.set("key", "value")
Azu.cache.set("key", "value", expires_in: 1.hour)

Parameters:

• key : String - Cache key

• value : String - Value to store

• expires_in : Time::Span? - Optional TTL

get

Retrieve a value.

value = Azu.cache.get("key")  # => String?

Parameters:

• key : String - Cache key

Returns: String? - Cached value or nil

fetch

Get or compute a value.

value = Azu.cache.fetch("key", expires_in: 1.hour) do
  expensive_computation
end

Parameters:

• key : String - Cache key

• expires_in : Time::Span? - Optional TTL

• &block - Block to compute value if missing

Returns: String - Cached or computed value

delete

Remove a value.

Azu.cache.delete("key")

Parameters:

• key : String - Cache key

exists?

Check if key exists.

if Azu.cache.exists?("key")
  # Key is cached
end

Parameters:

• key : String - Cache key

Returns: Bool

clear

Remove all cached values.

Azu.cache.clear

increment

Increment a numeric value.

Azu.cache.increment("counter")        # => 1
Azu.cache.increment("counter")        # => 2
Azu.cache.increment("counter", by: 5) # => 7

Parameters:

• key : String - Cache key

• by : Int32 - Increment amount (default: 1)

Returns: Int32 - New value

decrement

Decrement a numeric value.

Azu.cache.decrement("counter")
Azu.cache.decrement("counter", by: 5)

Parameters:

• key : String - Cache key

• by : Int32 - Decrement amount (default: 1)

Returns: Int32 - New value

expire

Set expiration on existing key.

Azu.cache.expire("key", 30.minutes)

Parameters:

• key : String - Cache key

• ttl : Time::Span - Time to live

RedisStore-Specific Methods

delete_matched

Delete keys matching a pattern.

Azu.cache.delete_matched("user:*")

Parameters:

• pattern : String - Glob pattern

ttl

Get remaining time to live.

remaining = Azu.cache.ttl("key")  # => Time::Span?

Parameters:

• key : String - Cache key

Returns: Time::Span? - Remaining TTL or nil

Cache Patterns

Cache-Aside

def get_user(id : Int64) : User?
  cache_key = "user:#{id}"

  cached = Azu.cache.get(cache_key)
  return User.from_json(cached) if cached

  user = User.find?(id)
  if user
    Azu.cache.set(cache_key, user.to_json, expires_in: 15.minutes)
  end

  user
end

Write-Through

class User
  after_save :update_cache
  after_destroy :remove_from_cache

  private def update_cache
    Azu.cache.set("user:#{id}", to_json, expires_in: 1.hour)
  end

  private def remove_from_cache
    Azu.cache.delete("user:#{id}")
  end
end

Cache Stampede Prevention

def fetch_with_lock(key : String, expires_in : Time::Span, &)
  # Try cache first
  cached = Azu.cache.get(key)
  return cached if cached

  # Try to acquire lock
  lock_key = "lock:#{key}"
  if Azu.cache.set(lock_key, "1", expires_in: 10.seconds, nx: true)
    begin
      value = yield
      Azu.cache.set(key, value, expires_in: expires_in)
      value
    ensure
      Azu.cache.delete(lock_key)
    end
  else
    # Wait and retry
    sleep 100.milliseconds
    Azu.cache.get(key) || yield
  end
end

Configuration Example

Azu.configure do |config|
  if ENV["AZU_ENV"] == "production"
    config.cache = Azu::Cache::RedisStore.new(
      url: ENV["REDIS_URL"],
      pool_size: 10,
      namespace: "myapp:production",
      default_ttl: 1.hour
    )
  else
    config.cache = Azu::Cache::MemoryStore.new(
      max_size: 1000,
      default_ttl: 15.minutes
    )
  end
end

See Also

• How to Set Up Memory Cache

• How to Set Up Redis Cache