Batch Transactions

Batch lets you package multiple transactions together and execute them as a single unit. It eliminates the risk of partial completion and unexpected outcomes, giving you a more reliable and predictable experience for complex operations. Up to eight transactions can be submitted in a single batch.

Some potential uses for Batch include the following.

• All or nothing: You can mint an NFT and create an offer for it in one transaction. If the offer creation fails, the NFT mint is reverted as well.
• Trying out a few offers: Submit multiple offers with different amounts of slippage, but only one will succeed.
• Platform fees: Package platform fees within the transaction itself, simplifying the process.
• Swaps (multi-account): Trustless token/NFT swaps between multiple accounts.
• Withdrawing accounts (multi-account): Attempt a withdrawal from your checking account, and if that fails, withdraw from your savings account instead.

Batch transactions are comprised of the outer transaction, the wrapper Batch transaction itself, and the inner transactions, each of which is executed atomically. The precise way that the inner transactions are processed is determined by the batch mode.

Batch Mode

There are four possible batch modes: ALLORNOTHING, ONLYONE, UNTILFAILURE, and INDEPENDENT.

All or Nothing

In ALLORNOTHING mode, all inner transactions must succeed for any one of them to succeed.

Only One

ONLYONE mode means that the first transaction to succeed is the only one to succeed. All other transactions either failed or were never tried.

Until Failure

UNTILFAILURE applies all transactions until the first failure. All transactions after the first failure are not applied.

Independent

All transactions are applied, even if one or more of the inner transactions fail.

Raw Transactions

The RawTransactions object is a container for the list of transactions to be applied. You can include up to eight transactions in a sincle batch. The transactions can come from one account or multiple accounts.

Each inner transaction:

• must contain a BatchTxn field.
• must not have a sequence number. It must use a sequence number value of 0.
• must not have a fee. It must use a fee value of 0.
• must not be signed (the global transaction is already signed by all relevant parties). They must instead have an empty string ("") in the SigningPubKey and TxnSignature fields.

A transaction is considered a failure if it receives any result that is not tesSUCCESS.

The RawTransactions field is not included in the validated transaction, nor is it used to compute the outer transaction signature(s), since all transactions are included separately as a part of the ledger.

BatchTxn

The BatchTxn inner object must be included in any inner transaction of a Batch transaction. It prevents hash collisions between identical transactions (since sequence numbers aren't included). It ensures that every transaction has a sequence number associated with it, so that created ledger objects that use it in their ID generation can still operate. It allows users to more easily organize their transactions in the correct order.

It captures the account submitting the outer transaction, the sequence number of the outer transaction, the sequence number of the outer transaction. If it is a multi-account transaction, it captures the next available sequence number in the inner transaction's account.

Batch Signers

BatchSigners operates similarly to multisign on the XRPL. It's only needed if multiple accounts' transactions are included in the Batch transaction. Otherwise, the normal transaction signature provides the same security guarantees. Every account that has at least one inner transaction, excluding the outer account, must have a BatchSigners object.

Transaction IDs

TxnIDs conatains a list of the transaction hashes/IDs for all transactions contained in RawTranscations. This is the only information about the inner transactions that is stored on the ledger within the Batch transaction, since the inner transactions themselves have their own transactions on the ledger. The hashes in TxnIDs must be in the same order as the inner transactions in RawTransactions.

Fee

The fee for the outer transaction is twice the base fee (a total of 20 drops when there is no fee escalation), plus the sum of the transaction fees of all the inner transactions (which incorporates factors like higher fees for multisign or AMMCreate).

The fees for the individual inner transactions are paid in the outer transaction rather than the inner transactions themselves, to ensure that fee escalation is calculated on the total cost of the batch transaction and not just the overhead.

Metadata

Inner transactions are committed separately to the ledger and therefore have separate metadata. This ensures better backward compatibility for legacy systems, so that they can support Batch transactions without needing changes to their systems.

For example, a ledger that only has one Batch transaction containing 2 inner transactions would look like this:

[ OuterTransaction, InnerTransaction1, InnerTransaction2 ]

Outer Transaction

Each outer transaction contains the metadata for its sequence and fee processing, not for the inner transaction processing.

There is also a list of which transactions are actually processed, which is useful for the ONLYONE and UNTILFAILURE modes, since those might only process a subset of transactions. It can also hellp with debugging all modes. This section is called BatchExecutions. It contains a list of objects with the TransactionHash and TransactionResult for every transaction processed (whether or not it succeeds).

It's possible that not every transaction is included in the list. For example, when usingONLYONE mode, once a transaction succeeds, all other transactions are skipped.

Transactions are only included in the ledger if their result code is tesSuccess and the outer transaction has a result code of tesSuccess. For example, an inner transaction might have a result code of tesSuccess without being included in the ledger if you use the ALLORNOTHING mode and another transaction in the batch fails.

Inner Transaction

Each inner transaction contains the metadata for its own processing. Only the inner transactions that are actually committed to the ledger are included. This makes it easier for legacy systems to process Batch transactions as if they were normal.

There is also a pointer back to the parent outer transaction (parent_batch), for ease of development (similar to the nftoken_id field).

Edge Cases

Inner transactions don't have Sequences or TicketSequences, unlike a normal transaction. This causes some problems when it comes to transaction processing, due to a few edge cases.

Ledger Object ID Generation

Some objects, such as offers and escrows, use the sequence number of the creation transaction as a part of their ledger entry ID generation, to ensure uniqueness of the IDs.

To get around this, in single-account Batch transactions, a phantom sequence number is used instead. The phantom sequence number is equal to BatchTxn.OuterSequence + BatchTxn.BatchIndex.

Multi-account transactions use the same phantom sequence number strategy, using BatchTxn.Sequence + BatchTxn.BatchIndex, since the outer sequence doesn't map to the inner transaction's account.

Sequence Number Handling

Sequence numbers are always consumed (i.e. the AccountRoot's Sequence is incremented) if any inner transactions are processed. A transaction counts as being "processed" if it is applied to the ledger (that is, if a tec or tes error is received). The sequence number for each account is incremented by the total number of inner transactions included in the Batch transaction, to avoid any hash collisions.

Security Trust Assumptions

Regardless of how many accounts' transactions are included in a Batch transaction, all accounts need to sign the collection of transactions.

Single Account

In the single account case, the single account must approve all of the transactions it is submitting. No other accounts are involved.

Multi Account

The multi-account case is a bit more complicated and is best illustrated with an example.

Alice and Bob are conducting a trustless swap via a multi-account Batch, with Alice providing 1000 XRP and Bob providing 1000 USD. Bob submits the Batch transaction, so Alice must provide her part of the swap to him.

If Alice provides a fully autofilled and signed transaction to Bob, Bob can submit Alice's transaction on the ledger without submitting his and receive the 1000 XRP without losing his 1000 USD. Therefore, the inner transactions must be unsigned.

If Alice just signs her part of the Batch transaction, Bob can modify his transaction to only provide 1 USD instead, thereby getting his 1000 XRP at a much cheaper rate. Therefore, the entire Batch transaction (and all its inner transactions) must be signed by all parties.