Consensus Deep Dive

Sei uses a Tendermint-based consensus engine tuned for high-throughput EVM workloads. This guide summarises the latest behavioural changes so validator operators and infrastructure teams can keep nodes healthy.

Covers sei-tendermint@02c9462f1 (duplicate transaction cache sizing) and the current vote-extension posture.

Key Concepts

Consensus Algorithm	Tendermint BFT with instant finality and 2/3 voting power requirement.
Block Time Target	~1s.
Mempool Mode	Parallel check with duplicate transaction cache (LRU) sized via `mempool.cache_size`.
Vote Extensions	Disabled on mainnet. Enabling is irreversible (see below).

Duplicate Transaction Cache (Sep 2025)

sei-tendermint@02c9462f1 fixes the maximum size for the duplicate transaction cache. Previously, cached entries could exceed the intended limit when keys exceeded the configured length.

Ensure config.toml has an appropriate mempool.cache_size (default: 10,000).
If you run large validators, consider bumping to 20,000 while monitoring memory usage. The cache now enforces the cap precisely.
Removing transactions via RPC or after inclusion also clears them from the cache thanks to the same patch.

Vote Extensions

Vote extensions remain disabled for public Sei networks.
types/params.go enforces that once enabled, they cannot be turned off ("vote extensions cannot be disabled once enabled").
Operators should watch release notes before toggling any configuration that references vote extensions.

Operational Best Practices

Keep mempool.recheck disabled unless you need re-validation after app updates; recheck increases consensus latency.
Monitor consensus/height and mempool/txs Prometheus metrics. Spikes in cached entries without block inclusion may indicate upstream spam.
Use seid unsafe-reset-all cautiously; it clears the cache and state. Prefer state sync or snapshots when recovering from consensus stalls.

Troubleshooting

Error	Cause	Fix
`Duplicate tx errors after upgrade`	Cache size too small for current traffic.	Increase `mempool.cache_size` in `config.toml` and restart the node.
`Unexpected vote extension logs`	Experimental configuration toggled vote extensions.	Revert the change; once enabled the protocol expects extension payloads from validators.
`Consensus halt around upgrade height`	Nodes running mixed binaries or stale state.	Ensure all validators run the same release and execute a coordinated upgrade with state sync ready.

/node/technical-reference – config.toml deep dive.
/node/troubleshooting – crash and panic handling for validators.
rpc-gas-accounting – gas flow ties into finalised blocks.