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A blockchain has no central database. Thousands of independent nodes each hold a copy of the ledger, and consensus is the rule set they use to agree on which transactions happened and in what order. The mechanism a chain picks determines three things you care about as a data consumer: how fast a block appears, how confident you can be that it will stay, and whether “the latest block” means the same thing to everyone.

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The main families

Rollups are not a separate consensus mechanism so much as a separate trust assumption. A rollup inherits finality from the chain it settles to — usually Ethereum — which is why rollup blocks appear in under a second but take much longer to become truly irreversible.

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Why this changes your data

Block time sets your best-case latency. A chain that produces a block every 400ms can deliver an event faster than one that produces a block every 10 minutes. No pipeline improves on the chain’s own cadence. Finality style sets your confirmation cost. On a BFT chain, a committed block will never be discarded, so Allium can serve it immediately. On a PoW chain, the most recent blocks are genuinely uncertain, so serving them immediately means occasionally serving data that gets undone. See Transaction finality. Fork frequency sets your correction rate. Chains with fast blocks and probabilistic finality fork often — usually by a single block, resolved within seconds. Each fork is a set of transactions that briefly existed and then did not. See Reorgs. Block structure differs by family. A PoW chain like Bitcoin has blocks of UTXO-based transactions with no smart-contract execution trace. Ethereum has blocks, transactions, logs, and traces. Solana has slots, and not every slot produces a block. Cosmos chains emit typed events rather than EVM logs. This is why Allium’s per-chain schemas are not identical — see the Data Catalog.

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Two mechanisms worth knowing in detail

Ethereum validators propose one block per slot, and slots are grouped into epochs of 32. Validators vote on epoch boundaries, and once two consecutive epochs have been justified by a supermajority of stake, the earlier one is finalized — reverting it would require an attacker to burn a large fraction of all staked ETH.So an Ethereum block passes through three states: proposed (visible immediately, revertible), justified, and finalized (roughly 13 minutes later). Most applications do not wait for finalization; they wait for a fixed number of confirmations, which is what Allium does by default.
Solana does not express confidence as a block count. It exposes three commitment levels on its RPC interface:
  • processed — the node has seen the block; it may not be voted on
  • confirmed — a supermajority of the cluster has voted for the block
  • finalized — the block is rooted and will not be rolled back
Allium ingests Solana at the confirmed commitment level, which is the standard choice for near-realtime data: it excludes unvoted forks while avoiding the extra delay of waiting for a root.

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Next steps