Global counters

Say you want a sign in the lobby that shows how many times the boss has been killed, across every server. Every server adds to the number all the time. If they all wrote to one key, that key would run out of writes fast. A counter spreads the adds out and adds them up for you.

Counters are for stats you show. They're not for gold or anything a player owns: that belongs in the player's data.

1. Declare the counters

Counters live in a store of their own. Add it to Stores:

local StatsStore = Ledger.New({
	Name = "GlobalStats",
	Keys = "String",
	Default = {},
	MustExist = false,
	Erasable = false,
	Totals = {
		GoldSpent = {},
		BossKills = {},
	},
})

This store only holds counters, so it has no data or reducer of its own. Each name in Totals is one counter, and starts at 0.

2. Add to a counter

Put this in a ModuleScript called GlobalStats in ServerStorage:

--!strict
local ServerStorage = game:GetService("ServerStorage")

local Stores = require(ServerStorage.Stores)

local StatsStore = Stores.StatsStore

-- Adds to a counter in the background. Call it only once the thing you count has saved.
local function Add(Name: string, Amount: number)
	task.spawn(function()
		local Ok, Why = StatsStore:Bump(Name, Amount)
		if not Ok and Why ~= "Unresolved" then
			warn("Couldn't count", Name, Why)
		end
	end)
end

-- The counter's total, or nil if it can't be read right now.
local function Read(Name: string): number?
	local Total = StatsStore:Total(Name, 60)
	return Total
end

return {
	Add = Add,
	Read = Read,
}

Bump adds to the counter. It waits for the next batch, which can take up to a minute, because each server saves its adds together instead of one by one. That's why Add runs it in task.spawn: never make a player wait for it.

Add only once the thing you're counting has actually saved:

local Ok = Session:Commit({ Kind = "SpendGold", Amount = 25 })
if Ok then
	GlobalStats.Add("GoldSpent", 25)
end

A counter is separate from the player's data. If you add first and the purchase then fails, the counter still went up.

Amount is a whole number, and it can be negative to take some away.

What Bump answers

For a stat on a sign, missing the odd add is fine, so Add just warns. Answers has the rest.

3. Show the total

--!strict
local ServerStorage = game:GetService("ServerStorage")

local GlobalStats = require(ServerStorage.GlobalStats)

local REFRESH_SECONDS = 60

while true do
	local Kills = GlobalStats.Read("BossKills")
	if Kills then
		workspace:SetAttribute("BossKills", Kills)
	end

	task.wait(REFRESH_SECONDS)
end

Total(Name, 60) answers the counter. It reuses an answer up to 60 seconds old, and otherwise reads a copy that all your servers share, so it usually costs no DataStore requests. Read it about once a minute, not every frame. A new add can take a few minutes to show up in the total.

Changing counters later

You can add new counters to Totals at any time. Don't rename one: a new name is a new counter that starts at 0.

Next: Changing data