inject_slow_query.rb

#!/usr/bin/env ruby
# frozen_string_literal: true

# WARNING: This will lock up CPU on the target Redis instance. Never run against production.
#
# Copyright 2020 Scribd, Inc.

require 'logger'
require 'redis'
require_relative 'lib/slowlog_check'

LOGGER = Logger.new($stdout)
LOGGER.level = Logger::WARN

REDIS = SlowlogCheck::Redis.new(
  host: ENV.fetch('REDIS_HOST')
).redis_rb

if ARGV[0].nil?
  raise "Specify milliseconds to inject as the first positional argument to `#{__FILE__}`"
else
  milliseconds = ARGV[0].to_i
end

SCRIPT = <<~HEREDOC
  -- From https://medium.com/@stockholmux/simulating-a-slow-command-with-node-redis-and-lua-efadbf913cd9
  local aTempKey = "a-temp-key"
  local cycles
  redis.call("SET",aTempKey,"1")
  redis.call("PEXPIRE",aTempKey, #{milliseconds})
  for i = 0, #{15_000 * milliseconds}, 1 do
  	local apttl = redis.call("PTTL",aTempKey)
  	cycles = i;
  	if apttl == 0 then
  		break;
  	end
  end
  return cycles
HEREDOC

LOGGER.info REDIS.eval(SCRIPT)