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Queue, Consensus: separate out queue mechanics, clarify how ledgers are calculated

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mDuo13
2018-09-12 18:49:51 -07:00
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content/concepts/payment-system-basics/transaction-basics/transaction-cost.md
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@@ -60,34 +60,7 @@ See also: [Fee Escalation explanation in `rippled` repository](https://github.co
When `rippled` receives a transaction that meets the server's local load cost but not the [open ledger cost](#open-ledger-cost), the server estimates whether the transaction is "likely to be included" in a later ledger. If so, the server adds the transaction to the transaction queue and relays the transaction to other members of the network. Otherwise, the server discards the transaction. The server tries to minimize the amount of network load caused by transactions that would not pay a transaction cost, since [the transaction cost only applies when a transaction is included in a validated ledger](#transaction-costs-and-failed-transactions).
When the current open ledger closes and the server starts a new open ledger, the server starts taking transactions from the queue to include in the new open ledger. The transaction queue is sorted with the transactions that would pay the highest transaction cost first, proportional to the [reference cost](#reference-transaction-cost) of those transactions. Transactions that pay the same transaction cost are queued in the order the server receives them.
**Note:** When `rippled` queues a transaction, the provisional [transaction response code](transaction-results.html) is `terQUEUED`. This means that the transaction is likely to succeed in a future ledger version. As with all provisional response codes, the outcome of the transaction is not final until the transaction is either included in a validated ledger, or [rendered permanently invalid](finality-of-results.html).
#### Queuing Restrictions
The `rippled` server uses a variety of heuristics to estimate which transactions are "likely to be included in a ledger." The current implementation uses the following rules to decide which transactions to queue:
* Transactions must be properly-formed and [authorized](transaction-basics.html#authorizing-transactions) with valid signatures.
* Transactions with an `AccountTxnID` field cannot be queued.
* A single sending address can have at most 10 transactions queued at the same time. In order for a transaction to be queued, the sender must have enough XRP to pay all the XRP costs of all the sender's queued transactions including both the `Fee` fields and the sum of the XRP that each transaction could send. [New in: rippled 0.32.0][]
* If a transaction affects how the sending address authorizes transactions, no other transactions from the same address can be queued behind it. [New in: rippled 0.32.0][]
* If the transaction includes a `LastLedgerSequence` field, the value of that field must be at least **the current ledger index + 2**.
#### Fee Averaging
[New in: rippled 0.33.0][]
If a sending address has one or more transactions queued, that sender can "push" the existing queued transactions into the open ledger by submitting a new transaction with a high enough transaction cost to pay for all of them. Specifically, the new transaction must increase the total transaction cost of the queued transactions from the same sending address, including the new transaction, to cover the [open ledger cost](#open-ledger-cost) of each transaction as it gets added to the ledger. The total must include the increased open ledger cost for each new transaction. The transactions must still follow the other [queuing restrictions](#queuing-restrictions) and the sending address must have enough XRP to pay the transaction costs of all the queued transactions.
This feature helps you work around a particular situation. If you submitted one or more transactions with a low cost, which got queued, you cannot send new transactions from the same address unless you do one of the following:
* Wait for the queued transactions to be included in a validated ledger, _or_
* Wait for the queued transactions to be permanently invalidated if the transactions have the [`LastLedgerSequence` field](reliable-transaction-submission.html#lastledgersequence) set, _or_
* [Cancel the queued transactions](cancel-or-skip-a-transaction.html) by submitting a new transaction with the same sequence number.
If none of the above occur, transactions can stay in the queue for a theoretically unlimited amount of time, while other senders can "cut in line" by submitting transactions with higher transaction costs. Since signed transactions are immutable, you cannot increase the transaction cost of the queued transactions to increase their priority. If you do not want to invalidate the previously submitted transactions, fee averaging provides a workaround. If you increase the transaction cost of your new transaction to compensate, you can ensure the queued transactions are included in an open ledger right away.
For more information on queued transactions, see [Transaction Queue](transaction-queue.html).
## Reference Transaction Cost