A performance optimisation for keyword-heavy scripts

I use quite a few scripts that get and decode keywords added to objects. These usually take the form of "MYTHINGS, thingone=bim, thingtwo=bem, ", with MYTHINGS being an event script trigger, also used by a resident, and the rest being equals separated parameters. The residents usually check for updated keywords periodically using the event script trigger keyword, hence the function below.

I found that GetCBusByKw was just too slow for often use, so came up with the following SQLite query. As the comment says, in my case this approach is usually 2x as fast.

Code:

--[[
Get applicable groups and keywords
Usually executes twice as fast as GetCBusByKw() overall, especially as equals separated keywords are processed here at the same time, and net/app/group/channel is pre-separated.
--]]
local function getGroups(kw)
  local grps = {}
  for _, t in ipairs(db:getall("SELECT o.address, o.tagcache, o.name FROM objects AS o JOIN objecttags AS ot ON o.id=ot.object WHERE ot.tag='"..kw.."'")) do
    local alias = knxlib.decodega(t.address)
    local parts = alias:split('/')
    grps[alias] = { name = t.name, keywords = t.tagcache:gsub(', ',','), net = tonumber(parts[1]), app = tonumber(parts[2]), group = tonumber(parts[3]), channel = tonumber(parts[4]), }
    local tags = {}
    local tg
    for _, tg in ipairs(grps[alias].keywords:split(',')) do
      parts = tg:split('=')
      if parts[2] then tags[parts[1]] = parts[2] else tags[parts[1]] = -1 end
    end
    grps[alias].tags = tags
  end
  return grps
end

It should probably strip extra leading/trailing spaces in the ipairs(grps[alias].keywords:split(',')) loop, and that could be accomplished with a function like this to trim parts[1] and parts[2]:

Code:

local function trim(s) if s ~= nil then return s:match('^%s*(.-)%s*$') else return nil end end

I set the keywords without an equals to have a table value of -1, as nil would remove them from the table. Checking parameter values in other code later essentially says, "If it's not -1 then it's a key/value parameter, otherwise it's just a key..."

By the way, for a fascinating look inside the DB schema, execute log(db:getlist('SELECT sql FROM sqlite_master')) in a script.