gistfile1.lua

local res
local mover
-- step 1: ensure the target database is flushed
redis.call('select', ARGV[1])
redis.call('flushdb')
-- step 2: fetch keys to transfer from database 0, that is one and only master
redis.call('select', 0)
res = redis.call('keys', '*')
for key, value in pairs(res)
  do
    -- this select is imperative to make sure we don't start dumping from the target
    redis.call('select', 0)
    mover = redis.call('DUMP', value)
    redis.call('select', ARGV[1])
    -- do not care about TTLs, we are not testing that
    redis.call('RESTORE', value, 0, mover)
  end
-- leave redis select as you found it, just in case
redis.call('select', ARGV[1])
return 1