Market making

The Alcor swap router reads book.alcor together with the AMM pools. When your quotes beat a pool, swaps fill against them — so liquidity in the book reaches every swap on Alcor, not only traders on the order book page.

Quote with one transactionCopy Anchor Link

Update a market with one transaction: first cancel the orders that moved, then placeorder the new ones. Actions run in order, so the funds the cancels release are already available to the new orders.

• Flag 8, post-only-skip. If the price moves while your transaction is on its way, a quote that would now cross the book is simply not placed, and the rest of the batch goes through. With plain post-only (1) one crossing quote reverts the whole transaction — including the cancels, which leaves your old quotes standing exactly when the price has run.
• expires_at. Give every quote an expiry, for example 60 seconds ahead in block time. If your bot stops, its quotes stop trading on their own. Refresh them well before they expire: the router treats an order as expired 10 seconds early.
• Requote threshold. Leave an order in place while its price is within a few basis points of where you want it. Every update costs CPU, and a new order loses its place in the queue.
• Start and stop with cancelall. It removes up to 100 orders per call; call again while it returns 100.

FillsCopy Anchor Link

Subscribe to your account on the order book API:

{"op": "subscribe", "channel": "account:alice"}

A trade event where owner is your account is a fill of your order: id is the order, qty the lots filled, qty_rem what is left. The events of your own transactions also come back in the transaction result (KeySigner.transact in the SDK).

Reading your own stateCopy Anchor Link

A node in read-mode = head shows a transaction only once a producer's block includes it. Reading your orders right after sending can return the state from before. Wait until the orders your transaction opened appear and the ones it cancelled disappear — the transaction's order_open and order_cancel events list them — or until the head is a few blocks past the transaction's block.

Things to knowCopy Anchor Link

• Self-trade prevention. Your own order in the way of your taker order is cancelled, not traded.
• Buy locks include the fee. A buy locks ceil(qty * price * (1 + fee_bps / 10000)); check it against your available quote with buyReserve.
• Dust. A maker remainder below min_notional after a partial fill is cancelled and refunded.
• Swaps sell whole lots. A swap of base sells floor(amount / lot_size) lots and returns the rest, so a large lot means larger change for swappers.

CPUCopy Anchor Link

Cancelling and placing about eight orders in one transaction costs roughly 1–1.6 ms of CPU. Re-quoting a market every few seconds adds up to several seconds of CPU a day per market.

On XPR, eosio::stakexpr is a voting stake and does not add CPU.