Iterating over JSON docs

This Lua code runs in redis. It iterates over some JSON docs, and applies some logic based on the user (if any) making the request. I'm sure there's a lot I can improve here.

local function iterAll(limit)
  local start = 0
  local stop = limit-1
  local ids = redis.call('zrevrange', 'questions-by-latest', start, stop)
  local i = 0
  local function it()
    i = i+1
    if i <= #ids then
      return ids[i]
    elseif i > #ids then
      start = start+limit
      stop = stop+limit
      i = 1
      ids = redis.call('zrevrange', 'questions-by-latest', start, stop)
      if #ids > 0 then
        return ids[i]
      end
    end
  end
  return it
end

local function filter(qid, optUid)
  local q = cjson.decode(redis.call('hget', 'questions', qid))
  if not q['is-active'] then return false end

  if optUid then
    local u = cjson.decode(redis.call('hget', 'users', optUid))
    if #u['ignored-tags'] > 0 then
      for idx, itag in ipairs(u['ignored-tags']) do
        for jdx, qtag in ipairs(q['tags']) do
          if itag == qtag then return false end
        end
      end
    end
  end

  return true
end

local offset = tonumber(ARGV[1])
local limit = tonumber(ARGV[2])

local optUid = false
if #ARGV == 3 then
  optUid = tonumber(ARGV[3])
end

local i = 0
local j = 0
local ids = {}
for qid in iterAll(limit) do
  if filter(qid, optUid) then
    i = i+1
    if i > (offset+limit) then break end
    if i > offset then
      j = j+1
      ids[j] = qid
    end
  end
end

return ids