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https://github.com/fluencelabs/tendermint
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78 lines
2.4 KiB
Markdown
78 lines
2.4 KiB
Markdown
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# ADR 005: Consensus Params
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## Context
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Consensus critical parameters controlling blockchain capacity have until now been hard coded, loaded from a local config, or neglected.
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Since they may be need to be different in different networks, and potentially to evolve over time within
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networks, we seek to initialize them in a genesis file, and expose them through the ABCI.
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While we have some specific parameters now, like maximum block and transaction size, we expect to have more in the future,
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such as a period over which evidence is valid, or the frequency of checkpoints.
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## Decision
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### ConsensusParams
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A new `ConsensusParams` is optionally included in the `genesis.json` file,
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and loaded into the `State`. Any items not included are set to their default value.
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A value of 0 is undefined (see ABCI, below). A value of -1 is used to indicate the parameter does not apply.
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No consensus critical parameters should ever be found in the `config.toml`.
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```
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type ConsensusParams struct {
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BlockSizeParams
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TxSizeParams
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BlockGossipParams
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}
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type BlockSizeParams struct {
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BlockSizeBytes int
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BlockSizeTxs int
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BlockSizeGas int
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}
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type TxSizeParams struct {
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TxSizeBytes int
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TxSizeGas int
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}
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type BlockGossipParams struct {
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BlockPartSizeBytes int
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}
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```
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The `ConsensusParams` can evolve over time by adding new structs that cover different aspects of the consensus rules.
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### ABCI
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#### InitChain
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InitChain currently takes the initial validator set. It should be extended to also take the ConsensusParams.
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In fact, it might as well just consume the whole Genesis.
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#### EndBlock
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The EndBlock response includes a `ConsensusParams`, which includes BlockSizeParams and TxSizeParams, but not BlockGossipParams.
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Other param struct can be added to `ConsensusParams` in the future.
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The `0` value is used to denote no change.
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Any other value will update that parameter in the `State.ConsensusParams`, to be applied for the next block.
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Tendermint should have hard-coded upper limits as sanity checks.
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## Status
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Proposed.
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## Consequences
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### Positive
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- Alternative capacity limits and consensus parameters can be specified without re-compiling the software.
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- They can also change over time under the control of the application
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### Negative
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- More exposed parameters is more complexity
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- Different rules at different heights in the blockchain complicates fast sync
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### Neutral
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