reverse.sharding.lua

-- Return keys with a given prefix for a particular node where there are a
-- known total of nodes. Uses the reamainder of the keys' hash values to
-- segment the keys.
function slice(prefix, index_and_total)
  local args = _split(index_and_total, "\t")
  if #args ~= 2 then
    return nil
  end

  local index = tonumber(args[1])
  local total = tonumber(args[2])

  local res = {}

  local keys = _fwmkeys(prefix)
  for i = 1, #keys do
    local key = keys[i]
    local url = string.sub(
      key,
      string.find(key, ":", string.find(key, ":", 1, true) + 1, true) + 1
    )

    local modulo = tonumber(string.sub(_hash("md5", url), 1, 10), 16) % total

    if modulo == index then
      table.insert(res, key)
    end
  end

  if #res == 0 then
    return nil
  end

  return table.concat(res, "\t")
end

tyrant.cache.lua

-- Retrieves a given key if its timestamp is fresher than cutoff.
-- If the key is non found or the timestamp is older than cutoff,
-- nil is returned.
function get_cache(key, cutoff)
  upto, upto_length = _process_timestamp(cutoff)
  if not upto then return nil end
  return _get_cache(key, upto, upto_length)
end

-- Compact all cached items having keys starting with prefix and
-- timestamp older than cutoff. Returns the number of compacted elements.
function compact_cache(prefix, cutoff)
  upto, upto_length = _process_timestamp(cutoff)
  if not upto then return nil end

  local compactions = 0
  local keys = _fwmkeys(prefix)

  for i = 1, #keys do
    local key = keys[i]
    if not _get_cache(key, upto, upto_length) then
        compactions = compactions + 1
    end
  end
  return compactions
end

function _process_timestamp(cutoff)
  local upto = tonumber(cutoff)
  local upto_length = string.len(cutoff)
  if upto and upto_length > 0 then
    return upto, upto_length
  end
  return nil
end

function _get_cache(key, upto, upto_length)
  local value = _get(key)
  if value then
    local stored_at = tonumber(string.sub(value, 1, upto_length))
    if stored_at < upto then
      if _out(key) then
        return nil
      end
    end
  end
  return value
end