perf(consensus): add simplistic block validation cache (cometbft#3070) (

#133)

Closes cometbft#2854

Follow up from cometbft#2960

This PR adds a simplistic 1-element block validation cache in
`BlockExecutor`. This addresses a performance bottleneck raised as part
of cometbft#2854

---

- [ ] Tests written/updated
- [ ] Changelog entry added in `.changelog` (we use
[unclog](https://github.com/informalsystems/unclog) to manage our
changelog)
- [ ] Updated relevant documentation (`docs/` or `spec/`) and code
comments
- [ ] Title follows the [Conventional
Commits](https://www.conventionalcommits.org/en/v1.0.0/) spec

---------

Co-authored-by: Sergio Mena <sergio@informal.systems>
Co-authored-by: Andy Nogueira <me@andynogueira.dev>

state/execution.go

@@ -40,6 +40,9 @@ type BlockExecutor struct {
 	mempool mempool.Mempool
 	evpool  EvidencePool
 
+	// 1-element cache of validated blocks
+	lastValidatedBlock *types.Block
+
 	logger log.Logger
 
 	metrics *Metrics
@@ -188,9 +191,11 @@ func (blockExec *BlockExecutor) ProcessProposal(
 // Validation does not mutate state, but does require historical information from the stateDB,
 // ie. to verify evidence from a validator at an old height.
 func (blockExec *BlockExecutor) ValidateBlock(state State, block *types.Block) error {
-	err := validateBlock(state, block)
-	if err != nil {
-		return err
+	if !blockExec.lastValidatedBlock.HashesTo(block.Hash()) {
+		if err := validateBlock(state, block); err != nil {
+			return err
+		}
+		blockExec.lastValidatedBlock = block
 	}
 	return blockExec.evpool.CheckEvidence(block.Evidence.Evidence)
 }
@@ -211,11 +216,12 @@ func (blockExec *BlockExecutor) ApplyVerifiedBlock(
 func (blockExec *BlockExecutor) ApplyBlock(
 	state State, blockID types.BlockID, block *types.Block,
 ) (State, error) {
-
-	if err := validateBlock(state, block); err != nil {
-		return state, ErrInvalidBlock(err)
+	if !blockExec.lastValidatedBlock.HashesTo(block.Hash()) {
+		if err := validateBlock(state, block); err != nil {
+			return state, ErrInvalidBlock(err)
+		}
+		blockExec.lastValidatedBlock = block
 	}
-
 	return blockExec.applyBlock(state, blockID, block)
 }