What is this?

A datastore library for Roblox with no session locks. You never write state. You write down the change you want, a function you own decides whether it is valid, and Ledger saves each change exactly once.

type PlayerData = {
	Gold: number,
	Items: { [string]: number },
}

type PlayerOps = {
	SpendGold: { Amount: number },
}

local PlayerStore = Ledger.New<<PlayerData, PlayerOps>>({
	Name = "PlayerData",
	Keys = "Player",
	Default = { Gold = 100, Items = {} },
	MustExist = false,
	Erasable = true,
	Reducer = function(Data, Op)
		if Op.Kind == "SpendGold" then
			if Op.Amount > Data.Gold then
				return nil -- refused, on every server
			end
			local New = table.clone(Data)
			New.Gold -= Op.Amount
			return New
		end
		return nil
	end,
})

local Session = PlayerStore:Load(Player)
if Session then
	local Ok, Why = Session:Commit({ Kind = "SpendGold", Amount = 25 })
	if not Ok then
		warn("Couldn't spend gold:", Why)
	end
end

Two servers spend the same 100 gold at once: the reducer accepts one and refuses the other. Every server agrees, every time, and every call says what happened.

A session lock serializes writers. A validating fold makes the invalid state unreachable, which is a stronger guarantee that also costs nothing when a server crashes: no lease to wait out, no locked player join stall, no side channel to touch someone offline or on another server. Changes are ops with names, and a reducer validates them.

Features

• Lock free | every server, same result, no locks
• Cross server | write to any player, even offline
• Entity stores | clans, listings, world records
• Transactions | up to 29 players or keys, all move or none do
• Balances | gold keeps moving while a trade is in progress
• Limited items | sold from every server, never oversold
• Global counters | every server adds, reading is free
• Migrations | old servers can't corrupt new data
• Idempotent | a write retried applies one time
• Typed ops | name them once, every write is checked
• Loud misuse | bad code throws, immediately

Installing

Wally

[dependencies]
Ledger = "xoifaii/ledger@7.0.2"

Model file: insert the Ledger module anywhere server side.

roblox-ts

npm install @xoifail/ledger

The same types work for TypeScript: see Types.

License

This project has the MIT License.