pkg/local_object_storage/pilorama/boltdb.go

@@ -1161,6 +1161,7 @@ func (t *boltForest) fillSortedChildren(b *bbolt.Bucket, nodeIDs MultiNode, h *f
 					lastFilename = nil
 					nodes = nil
 					length = actualLength + 1
+					count = 0
 					c.Seek(append(prefix, byte(length), byte(length>>8)))
 					c.Prev() // c.Next() will be performed by for loop
 				}

pkg/local_object_storage/pilorama/forest_test.go

@@ -1,11 +1,13 @@
 package pilorama
 
 import (
+	"bytes"
 	"context"
 	"crypto/rand"
 	"fmt"
 	mrand "math/rand"
 	"path/filepath"
+	"slices"
 	"strconv"
 	"strings"
 	"sync"
@@ -232,6 +234,65 @@ func BenchmarkForestSortedIteration(b *testing.B) {
 	}
 }
 
+// The issue which we call "BugWithSkip" is easiest to understand when filenames are
+// monotonically increasing numbers. We want the list of sorted filenames to have different length interleaved.
+// The bug happens when we switch between length during listing.
+// Thus this test contains numbers from 1 to 2000 and batch size of size 10.
+func TestForest_TreeSortedIterationBugWithSkip(t *testing.T) {
+	for i := range providers {
+		t.Run(providers[i].name, func(t *testing.T) {
+			testForestTreeSortedIterationBugWithSkip(t, providers[i].construct(t))
+		})
+	}
+}
+
+func testForestTreeSortedIterationBugWithSkip(t *testing.T, s ForestStorage) {
+	defer func() { require.NoError(t, s.Close()) }()
+
+	cid := cidtest.ID()
+	d := CIDDescriptor{cid, 0, 1}
+	treeID := "version"
+	treeAdd := func(t *testing.T, ts int, filename string) {
+		_, err := s.TreeMove(context.Background(), d, treeID, &Move{
+			Child:  RootID + uint64(ts),
+			Parent: RootID,
+			Meta: Meta{
+				Time: Timestamp(ts),
+				Items: []KeyValue{
+					{Key: AttributeFilename, Value: []byte(filename)},
+				},
+			},
+		})
+		require.NoError(t, err)
+	}
+
+	const count = 2000
+	treeAdd(t, 1, "")
+	for i := 1; i < count; i++ {
+		treeAdd(t, i+1, strconv.Itoa(i+1))
+	}
+
+	var result []MultiNodeInfo
+	treeAppend := func(t *testing.T, last *string, count int) *string {
+		res, cursor, err := s.TreeSortedByFilename(context.Background(), d.CID, treeID, MultiNode{RootID}, last, count)
+		require.NoError(t, err)
+		result = append(result, res...)
+		return cursor
+	}
+
+	const batchSize = 10
+	last := treeAppend(t, nil, batchSize)
+	for i := 1; i < count/batchSize; i++ {
+		last = treeAppend(t, last, batchSize)
+	}
+	require.Len(t, result, count)
+	require.True(t, slices.IsSortedFunc(result, func(a, b MultiNodeInfo) int {
+		filenameA := findAttr(a.Meta, AttributeFilename)
+		filenameB := findAttr(b.Meta, AttributeFilename)
+		return bytes.Compare(filenameA, filenameB)
+	}))
+}
+
 func TestForest_TreeSortedIteration(t *testing.T) {
 	for i := range providers {
 		t.Run(providers[i].name, func(t *testing.T) {

pkg/local_object_storage/pilorama/heap.go

@@ -2,6 +2,8 @@ package pilorama
 
 import (
 	"container/heap"
+	"slices"
+	"strings"
 )
 
 type heapInfo struct {
@@ -28,9 +30,10 @@ func (h *filenameHeap) Pop() any {
 
 // fixedHeap maintains a fixed number of smallest elements started at some point.
 type fixedHeap struct {
-	start *string
+	start  *string
-	count int
+	sorted bool
-	h     *filenameHeap
+	count  int
+	h      *filenameHeap
 }
 
 func newHeap(start *string, count int) *fixedHeap {
@@ -44,20 +47,39 @@ func newHeap(start *string, count int) *fixedHeap {
 	}
 }
 
+const amortizationMultiplier = 5
+
 func (h *fixedHeap) push(id MultiNode, filename string) bool {
 	if h.start != nil && filename <= *h.start {
 		return false
 	}
-	heap.Push(h.h, heapInfo{id: id, filename: filename})
+
-	if h.h.Len() > h.count {
+	*h.h = append(*h.h, heapInfo{id: id, filename: filename})
-		heap.Remove(h.h, h.h.Len()-1)
+	h.sorted = false
+
+	if h.h.Len() > h.count*amortizationMultiplier {
+		slices.SortFunc(*h.h, func(a, b heapInfo) int {
+			return strings.Compare(a.filename, b.filename)
+		})
+		*h.h = (*h.h)[:h.count]
 	}
 	return true
 }
 
 func (h *fixedHeap) pop() (heapInfo, bool) {
-	if h.h.Len() != 0 {
+	if !h.sorted {
-		return heap.Pop(h.h).(heapInfo), true
+		slices.SortFunc(*h.h, func(a, b heapInfo) int {
+			return strings.Compare(a.filename, b.filename)
+		})
+		if len(*h.h) > h.count {
+			*h.h = (*h.h)[:h.count]
+		}
+		h.sorted = true
+	}
+	if len(*h.h) != 0 {
+		info := (*h.h)[0]
+		*h.h = (*h.h)[1:]
+		return info, true
 	}
 	return heapInfo{}, false
 }