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- # ADR 004: Historical Validators
-
- ## Context
-
- Right now, we can query the present validator set, but there is no history.
- If you were offline for a long time, there is no way to reconstruct past validators. This is needed for the light client and we agreed needs enhancement of the API.
-
- ## Decision
-
- For every block, store a new structure that contains either the latest validator set,
- or the height of the last block for which the validator set changed. Note this is not
- the height of the block which returned the validator set change itself, but the next block,
- ie. the first block it comes into effect for.
-
- Storing the validators will be handled by the `state` package.
-
- At some point in the future, we may consider more efficient storage in the case where the validators
- are updated frequently - for instance by only saving the diffs, rather than the whole set.
-
- An alternative approach suggested keeping the validator set, or diffs of it, in a merkle IAVL tree.
- While it might afford cheaper proofs that a validator set has not changed, it would be more complex,
- and likely less efficient.
-
- ## Status
-
- Accepted.
-
- ## Consequences
-
- ### Positive
-
- - Can query old validator sets, with proof.
-
- ### Negative
-
- - Writes an extra structure to disk with every block.
-
- ### Neutral
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