MemoTTL is a thread-safe memoization utility for Ruby that supports TTL (Time-To-Live) and LRU (Least Recently Used) eviction. It's designed for scenarios where memoized values should expire after a period and memory usage must be constrained.
- Memoize method results with expiration (TTL)
- Built-in LRU eviction to limit memory usage
- Thread-safe with Monitor
- Easy integration via
include MemoTTL
Use memo_ttl when:
- You're calling a pure method multiple times with the same arguments
- The method is expensive (I/O, DB, parsing, computation)
- You want in-memory caching without Redis or external dependencies
- You need per-object isolation — not global cache key management
- You want a cache that’s automatically invalidated via TTL and LRU
Avoid using it when:
- The method is already fast (e.g., simple arithmetic, inline logic)
- You're calling it with unique arguments every time
- You need cross-request or cross-process persistence (use
Rails.cache)
Add this line to your application's Gemfile:
gem "memo_ttl"Afterwards:
bundle installrequire "memo_ttl"
class Calculator
include MemoTTL
def a_method_that_does_something(x)
sleep(2) # simulate slow process
x * 2
end
# use at the bottom due to Ruby's top-down evalation of methods
memoize :a_method_that_does_something, ttl: 60, max_size: 100
end
calc = Calculator.new
calc.a_method_that_does_something(5) # takes 2 seconds
calc.a_method_that_does_something(5) # returns instantly from cacheTo clear the cache:
calc.clear_memoized_method(:a_method_that_does_something)
calc.clear_all_memoized_methods
calc.cleanup_memoized_methodsrequire 'memo_ttl'
class TestController < ApplicationController
include MemoTTL
def index
result1 = test_method(1, 2)
result2 = test_method(1, 2)
result3 = test_method(5, 2)
result4 = test_method(1, 2)
result5 = test_method(1, 2)
result6 = test_method(3, 4)
render plain: <<~TEXT
Result 1: #{result1}
Result 2: #{result2}
Result 3: #{result3}
Result 4: #{result4}
Result 5: #{result5}
Result 6: #{result6}
TEXT
end
def test_method(x, y)
puts "Calling test_method(#{x}, #{y})"
x + y
end
def clean_up
clear_memoized_method(:test_method)
clear_all_memoized_methods
cleanup_memoized_methods
end
memoize :test_method, ttl: 10, max_size: 10
endOutput in Rails console:
Processing by TestController#index as HTML
Calling test_method(1, 2)
Calling test_method(5, 2)
Calling test_method(3, 4)