BEP-172(Draft): Improvement on BSC validator committing stability

BEP
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BEP-172: Improvement on BSC validator committing stability

1. Summary

This BEP introduces an update for parlia consensus about the behavior when slash happend, so that the network will be more stable and efficient.

2. Abstract

This BEP introduces an update for parlia consensus, which changes the timestamp and delay setting for offturn validators. When the validator inturn missed his turn to commit block, the block mined by the offturn validator selected randomly would be committed as soon as possible(4 or 3 seconds).

3. Status

This BEP is a draft

4. Motivation

Before this BEP, a slash would happen when a validator missed his turn to commit a valid block. It would take some time longer than expected 3 seconds for the specific block mined with the delay mechanism, and even worse with the calculation algorithm deciding how long would be delayed when the block mined by offturn validator could be committed. And it took quit a long time (might be more than 1 minute) for the network recovering back to the expected block committing order with expected time duration(3 seconds).

With this BEP we rewrite the calculation algorithm for the offturn validation delay time, so that it should be able to commit block in 4 seconds for the selected offturn validator when the inturn validator missed his turn. What’s more, the slash will not have bad influence on the future blocks which means the network will recover to expected block producing duration in time.

5. Specification

5.1 overall workflow

backoffTime (1)
backoffTime (1)1535×1533 311 KB

5.2 Remove recentlySigned validators from the candidate set

  • All validators would be involved to calculate the delay time when committing the block mined by himself currently, and when the inturn validator missed his turn, the fastest-with the smallest delay duration equals to 4 seconds-offturn validator might be the one that had signed recently which led to some other offturn validator be the valid selected one to commit block. This is how we observed a block be committed in more than 4 seconds when the slash happend. In this BEP, we remove the recently signed validators off from the candidate set for calculating delay duration from 1 seconds(then the duration would be 3+1=4 seconds) up.

5.3 Reduce minimum delay duration to be zero added to 3 seconds

  • When a slash happend, things would go wrong for quite a long time later on. For example, when inturn validator_A was slashed on block_100 and offturn validator_B took his place to commit the block of number 100. However validator_B should be inturn for committing block_101, then it would fail to commit block_101 since he had committed block_100 recently. So although there was actually no slash happend(all validator worked appropriately), we still need to delay some time (1 second or more) to wait for the offturn validator committing the block since the inturn validator had recently committed some block earlier.In this BEP, we reduce the shortest duration to zero second for this specific scenario which means blocks should be able to committed in expected duration (3 seconds) when all validators workd propriately.