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Transactions

Transactions are fundamental to updating the ledger in Move-based blockchains.

Types of Transactions​

In Move, there are two primary types of transactions:

  • User Transactions: Programmable transaction blocks that any user can submit to the network. They allow you to execute custom logic, interact with smart contracts, and transfer assets.
  • System Transactions: Exclusive to validators, these transactions are essential for network operations like epoch transitions and checkpointing. They help maintain the blockchain's integrity and performance.

Key Components of a Transaction​

Every transaction in Move includes essential metadata:

  • Sender Address: The account address initiating the transaction.
  • Gas Payment Object: An object reference used to pay for the transaction's execution and storage costs. This object must be owned by the sender and be of the type move::coin::Coin<MOVE>, representing the native currency.
  • Gas Price: The amount of native tokens per unit of gas the sender is willing to pay. This must be a positive integer.
  • Maximum Gas Budget: The upper limit of gas units the transaction can consume. Exceeding this budget will abort the transaction, affecting only the gas payment object by deducting the consumed gas.
  • Target Epoch: The specific epoch for which the transaction is intended.
  • Transaction Type: Specifies whether it's a call, publish, or native transaction, along with its associated data.
  • Authenticator: A cryptographic signature and public key pair that verifies the sender's identity.
  • Expiration Epoch: An optional deadline after which validators will consider the transaction invalid if not yet executed. By default, transactions have no expiration.

Transaction Workflow Example​

To illustrate how transactions interact with objects, consider the following scenario involving IOTA:

Initial Setup​

  • Object A: Contains 5 IOTA and belongs to Tom.
  • Object B: Holds 2 IOTA and belongs to John.

1: Tom Sends 1 IOTA to Alice​

Tom initiates a transaction to send 1 IOTA to Alice using Object A. The transaction results in:

  • Object A: Now has 4 IOTA and remains with Tom.
  • Object C: A new object with 1 IOTA belonging to Alice.

2: John Sends 2 IOTA to Anna​

Simultaneously, John sends his 2 IOTA to Anna. Since this transaction involves different objects, it executes in parallel, transferring ownership of Object B to Anna.

3: Anna Sends 2 IOTA to Tom​

Anna immediately sends the 2 IOTA to Tom. Tom now possesses:

  • Object A: 4 IOTA.
  • Object B: 2 IOTA (ownership transferred to Tom).

4: Tom Sends All IOTA to John​

Finally, Tom decides to send all his IOTA to John. The transaction consumes both Object A and Object B, combining them into:

  • Object D: A new object with 6 IOTA belonging to John.
  • Object A and Object B: Consumed and removed from the ledger.

Transaction and Data Constraints​

Move imposes certain limits to ensure network stability and security:

  • Maximum Transaction Size: Transactions have a byte-size limit to prevent excessive resource consumption.
  • Object Limits: There's a cap on the number of objects a transaction can read or modify.
  • Data Size Restrictions: Limits are placed on the size of data payloads within transactions.

You can find detailed limits in the protocol-config module of the Move repository, defined in the ProtocolConfig struct.

How Transactions Are Executed​

The following diagram outlines the execution flow of a transaction, showing the sequence of function calls across various modules:

Transaction Execution Flow

Question 1/2

What happens if the gas budget is exceeded during a transaction in IOTA?