BCI-3668 Optimise HeadTracker's memory usage (#14130)

* base benchmarks

* Reduce allocs noise from mocks in Backfill Benchmark

* Optimize HeadTracker's memory usage

* avoid .Parent race in confirmer

* optimise block history estimator heads usage

* update telemetry test to use new Parent and IsFinalized

* avoid redundant allocations

* Revert "avoid redundant allocations"

This reverts commit 76343e5.

* lint fixes

* remove redundant files

* drop cycle detection logic from head methods. Heads cycle prevention should be enough

* drop unused test

* nits

.changeset/short-shoes-crash.md

@@ -0,0 +1,5 @@
+---
+"chainlink": patch
+---
+
+Optimize HeadTracker's memory usage #internal

common/txmgr/confirmer.go

@@ -1148,10 +1148,11 @@ func hasReceiptInLongestChain[
 				}
 			}
 		}
-		if head.GetParent() == nil {
+
+		head = head.GetParent()
+		if head == nil {
 			return false
 		}
-		head = head.GetParent()
 	}
 }
 

core/chains/evm/client/simulated_backend_client.go

@@ -320,7 +320,15 @@ func (c *SimulatedBackendClient) SubscribeNewHead(
 			case h := <-ch:
 				var head *evmtypes.Head
 				if h != nil {
-					head = &evmtypes.Head{Difficulty: h.Difficulty, Timestamp: time.Unix(int64(h.Time), 0), Number: h.Number.Int64(), Hash: h.Hash(), ParentHash: h.ParentHash, Parent: lastHead, EVMChainID: ubig.New(c.chainId)}
+					head = &evmtypes.Head{
+						Difficulty: h.Difficulty,
+						Timestamp:  time.Unix(int64(h.Time), 0), //nolint:gosec
+						Number:     h.Number.Int64(),
+						Hash:       h.Hash(),
+						ParentHash: h.ParentHash,
+						EVMChainID: ubig.New(c.chainId),
+					}
+					head.Parent.Store(lastHead)
 					lastHead = head
 				}
 				select {

core/chains/evm/gas/block_history_estimator.go

@@ -655,12 +655,13 @@ func (b *BlockHistoryEstimator) FetchBlocks(ctx context.Context, head *evmtypes.
 	}
 
 	blocks := make(map[int64]evmtypes.Block)
+	earliestInChain := head.EarliestInChain()
 	for _, block := range b.getBlocks() {
 		// Make a best-effort to be re-org resistant using the head
 		// chain, refetch blocks that got re-org'd out.
 		// NOTE: Any blocks in the history that are older than the oldest block
 		// in the provided chain will be assumed final.
-		if block.Number < head.EarliestInChain().BlockNumber() {
+		if block.Number < earliestInChain.BlockNumber() {
 			blocks[block.Number] = block
 		} else if head.IsInChain(block.Hash) {
 			blocks[block.Number] = block

core/chains/evm/gas/block_history_estimator_test.go

@@ -515,7 +515,7 @@ func TestBlockHistoryEstimator_FetchBlocks(t *testing.T) {
 
 		head2 := evmtypes.NewHead(big.NewInt(2), b2.Hash, b1.Hash, uint64(time.Now().Unix()), ubig.New(testutils.FixtureChainID))
 		head3 := evmtypes.NewHead(big.NewInt(3), b3.Hash, b2.Hash, uint64(time.Now().Unix()), ubig.New(testutils.FixtureChainID))
-		head3.Parent = &head2
+		head3.Parent.Store(&head2)
 		err := bhe.FetchBlocks(tests.Context(t), &head3)
 		require.NoError(t, err)
 
@@ -570,7 +570,7 @@ func TestBlockHistoryEstimator_FetchBlocks(t *testing.T) {
 		// RE-ORG, head2 and head3 have different hash than saved b2 and b3
 		head2 := evmtypes.NewHead(big.NewInt(2), utils.NewHash(), b1.Hash, uint64(time.Now().Unix()), ubig.New(testutils.FixtureChainID))
 		head3 := evmtypes.NewHead(big.NewInt(3), utils.NewHash(), head2.Hash, uint64(time.Now().Unix()), ubig.New(testutils.FixtureChainID))
-		head3.Parent = &head2
+		head3.Parent.Store(&head2)
 
 		ethClient.On("BatchCallContext", mock.Anything, mock.MatchedBy(func(b []rpc.BatchElem) bool {
 			return len(b) == 2 &&
@@ -643,7 +643,7 @@ func TestBlockHistoryEstimator_FetchBlocks(t *testing.T) {
 		// head2 and head3 have identical hash to saved blocks
 		head2 := evmtypes.NewHead(big.NewInt(2), b2.Hash, b1.Hash, uint64(time.Now().Unix()), ubig.New(testutils.FixtureChainID))
 		head3 := evmtypes.NewHead(big.NewInt(3), b3.Hash, head2.Hash, uint64(time.Now().Unix()), ubig.New(testutils.FixtureChainID))
-		head3.Parent = &head2
+		head3.Parent.Store(&head2)
 
 		err := bhe.FetchBlocks(tests.Context(t), &head3)
 		require.NoError(t, err)

core/chains/evm/headtracker/head_saver.go

@@ -35,13 +35,12 @@ func NewHeadSaver(lggr logger.Logger, orm ORM, config commontypes.Config, htConf
 }
 
 func (hs *headSaver) Save(ctx context.Context, head *evmtypes.Head) error {
-	if err := hs.orm.IdempotentInsertHead(ctx, head); err != nil {
+	// adding new head might form a cycle, so it's better to validate cached chain before persisting it
+	if err := hs.heads.AddHeads(head); err != nil {
 		return err
 	}
 
-	hs.heads.AddHeads(head)
-
-	return nil
+	return hs.orm.IdempotentInsertHead(ctx, head)
 }
 
 func (hs *headSaver) Load(ctx context.Context, latestFinalized int64) (chain *evmtypes.Head, err error) {
@@ -51,7 +50,10 @@ func (hs *headSaver) Load(ctx context.Context, latestFinalized int64) (chain *ev
 		return nil, err
 	}
 
-	hs.heads.AddHeads(heads...)
+	err = hs.heads.AddHeads(heads...)
+	if err != nil {
+		return nil, fmt.Errorf("failed to populate cache with loaded heads: %w", err)
+	}
 	return hs.heads.LatestHead(), nil
 }
 

core/chains/evm/headtracker/head_tracker.go

@@ -11,14 +11,13 @@ import (
 
 	"github.com/smartcontractkit/chainlink/v2/common/headtracker"
 	commontypes "github.com/smartcontractkit/chainlink/v2/common/headtracker/types"
-	evmclient "github.com/smartcontractkit/chainlink/v2/core/chains/evm/client"
 	httypes "github.com/smartcontractkit/chainlink/v2/core/chains/evm/headtracker/types"
 	evmtypes "github.com/smartcontractkit/chainlink/v2/core/chains/evm/types"
 )
 
 func NewHeadTracker(
 	lggr logger.Logger,
-	ethClient evmclient.Client,
+	ethClient httypes.Client,
 	config commontypes.Config,
 	htConfig commontypes.HeadTrackerConfig,
 	headBroadcaster httypes.HeadBroadcaster,