AIP-88: Block Epilogue Transactions

AIP-88 covers block epilogue transactions, which are a new type of transaction that give information about the block after it has been executed. These transactions can only be created by the consensus and are not user-initiated. They contain information about gas usage in the block and will contain more information in the future.

It replaces the previous StateCheckpoint transaction type, which was used to “sometimes” signal the end of a block. The new BlockEpilogue transaction is now sometimes created at the end of a block instead, and it is guaranteed to be the last transaction in the block. The only case this does not apply is the last block of an epoch, which will have no BlockEpilogue transaction.

General FAQ

What is in the Block Epilogue Transaction?

The block epilogue transaction contains a BlockEndInfo enum. It is purposely designed to be an enum so that it can be extended in the future without breaking existing code. The current version is V0 and contains the following fields:

module 0x1::epilogue {
  enum BlockEndInfo {
    V0 {
      /// Whether block gas limit was reached
      block_gas_limit_reached: bool,
      /// Whether block output limit was reached
      block_output_limit_reached: bool,
      /// Total gas_units block consumed
      block_effective_block_gas_units: u64,
      /// Total output size block produced
      block_approx_output_size: u64,
    },
  }
}

These mainly contain information about the gas usage in the block for debugging purposes.

The JSON output will look like this:

{
    "version":"1912",
    "hash":"0x54a8efc93fc94f5b545dadb63da3d4dc192125c717b336dc446d55a5b553913f",
    "state_change_hash":"0xafb6e14fe47d850fd0a7395bcfb997ffacf4715e0f895cc162c218e4a7564bc6",
    "event_root_hash":"0x414343554d554c41544f525f504c414345484f4c4445525f4841534800000000",
    "state_checkpoint_hash":"0x841a43956ca09a02b1c1cdadc65f24c390170aa666015a2e8f7ec5c9d6a3875f",
    "gas_used":"0",
    "success":true,
    "vm_status":"Executed successfully",
    "accumulator_root_hash":"0x6561976b4560ff25239dffc6cada70e7008dd42fc4d3df2eca6a86b6d2ec384d",
    "changes":[],
    "timestamp":"1719263322836578",
    "block_end_info": {
        "block_gas_limit_reached":false,
        "block_output_limit_reached":false,
        "block_effective_block_gas_units":0,
        "block_approx_output_size":1163
    },
    "type":"block_epilogue_transaction"
}

Compatibility FAQ

What does this mean for my dApp?

If you process transactions in your dApp, and expect the last transaction in a block to be a StateCheckpoint, you will need to update your code to handle the BlockEpilogue transaction instead.

Note that, the BlockEpilogue transaction is guaranteed to be the last transaction of a block except for the last block of an epoch, which will not have a BlockEpilogue transaction.

What apps are likely to be affected?

Apps that index all transactions such as block explorers and centralized exchange indexer processors may be affected. However, most of these are informational and do not affect the core functionality of the dApp.

What can I do to process the new transaction type?

If you’re using the Aptos Go SDK or the Aptos TypeScript SDK, you can update to the latest version, which will automatically handle the new transaction type.