From f2b7e9f1446dd2825c5004e313448aee2a684f0e Mon Sep 17 00:00:00 2001
From: Steven Danna <danna@cockroachlabs.com>
Date: Wed, 22 Nov 2023 10:41:29 +0000
Subject: [PATCH] Revert "kv: store span by pointer in latch struct"

This reverts commit 831c61ded84ba2d5887736f7046a45c3cac3cd4c.
---
 pkg/kv/kvserver/spanlatch/manager.go      | 49 ++++++-----------------
 pkg/kv/kvserver/spanlatch/manager_test.go |  8 ----
 2 files changed, 13 insertions(+), 44 deletions(-)

diff --git a/pkg/kv/kvserver/spanlatch/manager.go b/pkg/kv/kvserver/spanlatch/manager.go
index a227e4a3aeb7..32fe84e42081 100644
--- a/pkg/kv/kvserver/spanlatch/manager.go
+++ b/pkg/kv/kvserver/spanlatch/manager.go
@@ -87,7 +87,7 @@ func Make(stopper *stop.Stopper, slowReqs *metric.Gauge) Manager {
 type latch struct {
 	*signals
 	id         uint64
-	span       *roachpb.Span
+	span       roachpb.Span
 	ts         hlc.Timestamp
 	next, prev *latch // readSet linked-list.
 }
@@ -109,36 +109,13 @@ func (la *latch) SafeFormat(w redact.SafePrinter, _ rune) {
 //go:generate ../../../util/interval/generic/gen.sh *latch spanlatch
 
 // Methods required by util/interval/generic type contract.
-func (la *latch) New() *latch    { return new(latch) }
-func (la *latch) ID() uint64     { return la.id }
-func (la *latch) SetID(v uint64) { la.id = v }
-func (la *latch) Key() []byte {
-	if la.span == nil {
-		return nil
-	}
-	return la.span.Key
-}
-func (la *latch) EndKey() []byte {
-	if la.span == nil {
-		return nil
-	}
-	return la.span.EndKey
-}
-func (la *latch) SetKey(v []byte) {
-	la.initSpan()
-	la.span.Key = v
-}
-func (la *latch) SetEndKey(v []byte) {
-	la.initSpan()
-	la.span.EndKey = v
-}
-
-// initSpan lazily initializes the latch's span field. Only used in tests.
-func (la *latch) initSpan() {
-	if la.span == nil {
-		la.span = new(roachpb.Span)
-	}
-}
+func (la *latch) ID() uint64         { return la.id }
+func (la *latch) Key() []byte        { return la.span.Key }
+func (la *latch) EndKey() []byte     { return la.span.EndKey }
+func (la *latch) New() *latch        { return new(latch) }
+func (la *latch) SetID(v uint64)     { la.id = v }
+func (la *latch) SetKey(v []byte)    { la.span.Key = v }
+func (la *latch) SetEndKey(v []byte) { la.span.EndKey = v }
 
 type signals struct {
 	done   signal
@@ -221,7 +198,7 @@ func newGuard(spans *spanset.SpanSet, pp poison.Policy) *Guard {
 			ssLatches := latches[:n]
 			for i := range ssLatches {
 				latch := &latches[i]
-				latch.span = &ss[i].Span
+				latch.span = ss[i].Span
 				latch.signals = &guard.signals
 				latch.ts = ss[i].Timestamp
 				// latch.setID() in Manager.insert, under lock.
@@ -310,9 +287,9 @@ func (m *Manager) CheckOptimisticNoConflicts(lg *Guard, spans *spanset.SpanSet)
 		tr := &snap.trees[s]
 		for a := spanset.SpanAccess(0); a < spanset.NumSpanAccess; a++ {
 			ss := spans.GetSpans(a, s)
-			for i := range ss {
-				search.span = &ss[i].Span
-				search.ts = ss[i].Timestamp
+			for _, sp := range ss {
+				search.span = sp.Span
+				search.ts = sp.Timestamp
 				switch a {
 				case spanset.SpanReadOnly:
 					// Search for writes at equal or lower timestamps.
@@ -584,7 +561,7 @@ func (m *Manager) waitForSignal(
 			// ourselves anyway, so we don't need to self-poison.
 			switch pp {
 			case poison.Policy_Error:
-				return poison.NewPoisonedError(*held.span, held.ts)
+				return poison.NewPoisonedError(held.span, held.ts)
 			case poison.Policy_Wait:
 				log.Eventf(ctx, "encountered poisoned latch; continuing to wait")
 				wait.poison.signal()
diff --git a/pkg/kv/kvserver/spanlatch/manager_test.go b/pkg/kv/kvserver/spanlatch/manager_test.go
index f34050536850..be8cc806cce1 100644
--- a/pkg/kv/kvserver/spanlatch/manager_test.go
+++ b/pkg/kv/kvserver/spanlatch/manager_test.go
@@ -18,7 +18,6 @@ import (
 	"strings"
 	"testing"
 	"time"
-	"unsafe"
 
 	"github.com/cockroachdb/cockroach/pkg/keys"
 	"github.com/cockroachdb/cockroach/pkg/kv/kvserver/concurrency/poison"
@@ -682,13 +681,6 @@ func TestLatchManagerWaitFor(t *testing.T) {
 	m.Release(lg3)
 }
 
-// TestSizeOfLatch tests the size of the latch struct.
-func TestSizeOfLatch(t *testing.T) {
-	var la latch
-	size := int(unsafe.Sizeof(la))
-	require.Equal(t, 56, size)
-}
-
 func BenchmarkLatchManagerReadOnlyMix(b *testing.B) {
 	for _, size := range []int{1, 4, 16, 64, 128, 256} {
 		b.Run(fmt.Sprintf("size=%d", size), func(b *testing.B) {