第1章 — 読み書き戦略: キャッシュの基本パターン

# Rails での Cache-Aside パターン
def find_product(id)
  cache_key = "product:#{id}"
  
  # 1. キャッシュを確認
  product = Rails.cache.read(cache_key)
  return product if product
  
  # 2. DB から取得
  product = Product.find(id)
  
  # 3. キャッシュに保存
  Rails.cache.write(cache_key, product, expires_in: 1.hour)
  
  product
end

class Ranking
  SOFT_TTL = 50.minutes
  HARD_TTL = 70.minutes
  CACHE_KEY = "ranking:popular"
 
  def self.fetch
    payload = Rails.cache.read(CACHE_KEY)
    if payload.nil? || Time.current >= payload[:refresh_at]
      schedule_refresh
    end
    return payload[:data] if payload
    regenerate
  end
 
  def self.schedule_refresh
    lock_key = "#{CACHE_KEY}/lock"
    if Rails.cache.write(lock_key, "1", unless_exist: true, expires_in: 1.minute)
      RefreshRankingJob.perform_async
    end
  end
end