BNB Smart Chain Mainnet is expected to have a scheduled hardfork upgrade named Euler at a block height of 18,907,621. The current block generation speed forecasts this to occur around June 22, 2022, at 08:00 (UTC). The validators and full node operators should upgrade their software version to  v1.1.11 by June 22.

1. Background Story

1.1 Who is Leonhard Euler?

This upgrade is named after Leonhard Euler in honor of his key contributions to mathematics and mechanics. He was a Swiss mathematician, and physicist widely regarded as one of the founders of graph theory and topology. x

1.2 What is a hardfork upgrade?

A hardfork is an upgrade that is not compatible with the previous release because some breaking changes are introduced in the latest release. A hardfork in BNB Smart Chain requires more than half of all validators to successfully upgrade to keep making blocks. If the existing full nodes in the network do not upgrade, they will not be able to receive and execute further blocks normally after the hardfork block height.

1.3 What happens during a network upgrade?

Logic changes will occur at block height 19,203,503 for this upgrade. After the activation of the upgrade, the blockchain is able to handle a series of new features and bug fixes.

2. How does this upgrade affect me?

2.1 As a full node operator

This release is breaking and you need to switch to v1.1.11. Upgrade instructions are (all the below should be done before the hardfork block height):

  1. If your node is already synced with the network, please download and compile the latest version
  2. Stop the geth process and restart it with v1.1.11.

2.2 What will happen if I forget to upgrade my full node in time?

If you cannot upgrade your software, you cannot sync with the upgraded BNB Smart Chain peer/validator nodes. You will not be able to connect or send transactions.

How to recover?

  1. Download and compile the latest version v1.1.11.
  2. Stop the geth process and restart it with v1.1.11.

2.3 As a developer

There are no changes to the EVM module. You do not need to do anything.

3. Upcoming Changes

3.1 BEP-127 Temporary Maintenance Mode for Validators

Due to the design of the Parlia consensus, the absence of the validator, even if it is due to scheduled maintenance, will cause instability and capacity loss of BSC due to the extra waiting time and chain reorganization for other validators. Introducing the Temporary Maintenance mode will stabilize the blocking rotation and maintain the capacity of BSC.

A validator can claim itself to enter temporary maintenance mode by sending a transaction to interact with the ValidatorSet smart contract. Temporary maintenance is supposed to last one or a few hours. The validator seat will be temporarily dropped from the block-producing rotation during maintenance. Since long-time offline maintenance is not encouraged, the validator will still be slashed if the maintenance lasts too long. To lower the impact from poorly-operating validators who forget to claim its maintenance, they will be forced to enter temporary maintenance mode too.

Check BEP-127 for more details.

3.2 BEP-131 Introduce candidate validators onto BNB Smart Chain

This BEP introduces candidate validators onto BSC to improve the liveness and robustness of the network.

BSC plans to introduce more validators, e.g. another 10 inactive validators, into the validator set as backups, which will be called "Candidates". Candidates will produce blocks and charge gas fees on the BNB Smart Chain mainnet, but with a much less chance than the active validator set of 21 elected. A decent motivation is expected to be maintained so that the candidate validators are willing to ensure the quality and help secure BNB Smart Chain.

The number of Candidate Validators is subject to the BSC governance. The BSC Mainnet will keep the same number of Active Validators and 0 Candidate Validators right after the Euler upgrade, and the later governance action will enlarge the Candidate Validator Set to allow new Candidate Validators to be set up.

Check BEP-131 for more details.

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