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How we scaled the GitHub API with a sharded, replicated rate limiter in Redis

• gkorland 6y ago
  The issue with this suggested implementation that it's not atomic and might cause some race conditions. local expires_at = tonumber(redis.call("get", expires_at_key)) if not expires_at or expires_at < current_time then -- this is either a brand new window, -- or this window has closed, but redis hasn't cleaned up the key yet -- (redis will clean it up in one more second) -- initialize a new rate limit window redis.call("set", rate_limit_key, 0) redis.call("set", expires_at_key, next_expires_at) Between the time the `get` is called and the `set` is called there might parallel call that might create the key and the `set` will override it.
  • ryanworl 6y ago
    Lua script execution is atomic in Redis. https://redis.io/commands/eval#atomicity-of-scripts https://redis.io/commands/eval#atomicity-of-scripts > Redis guarantees that a script is executed in an atomic way: no other script or Redis command will be executed while a script is being executed.
    • gkorland 6y ago
      You're right I completely missed that this is a Lua a script part, I was sure it's the Ruby code... (shame on me, shows how much I can't recognize Ruby code...)