membuffer: fix memory leak in red-black tree (#1483)

.github/workflows/test.yml

@@ -48,4 +48,5 @@ jobs:
         uses: golangci/golangci-lint-action@v2.5.2
         with:
           version: v1.55.2
+          skip-go-installation: true
 

internal/unionstore/memdb.go

@@ -239,7 +239,7 @@ func (db *MemDB) SelectValueHistory(key []byte, predicate func(value []byte) boo
 // GetFlags returns the latest flags associated with key.
 func (db *MemDB) GetFlags(key []byte) (kv.KeyFlags, error) {
 	x := db.traverse(key, false)
-	if x.isNull() {
+	if x.isNull() || x.isDeleted() {
 		return 0, tikverr.ErrNotExist
 	}
 	return x.getKeyFlags(), nil
@@ -337,17 +337,22 @@ func (db *MemDB) set(key []byte, value []byte, ops ...kv.FlagsOp) error {
 	// the NeedConstraintCheckInPrewrite flag is temporary,
 	// every write to the node removes the flag unless it's explicitly set.
 	// This set must be in the latest stage so no special processing is needed.
-	var flags kv.KeyFlags
+	flags := x.getKeyFlags()
+	if flags == 0 && x.vptr.isNull() && x.isDeleted() {
+		x.unmarkDelete()
+		db.count++
+		db.size += int(x.klen)
+	}
 	if value != nil {
-		flags = kv.ApplyFlagsOps(x.getKeyFlags(), append([]kv.FlagsOp{kv.DelNeedConstraintCheckInPrewrite}, ops...)...)
+		flags = kv.ApplyFlagsOps(flags, append([]kv.FlagsOp{kv.DelNeedConstraintCheckInPrewrite}, ops...)...)
 	} else {
 		// an UpdateFlag operation, do not delete the NeedConstraintCheckInPrewrite flag.
-		flags = kv.ApplyFlagsOps(x.getKeyFlags(), ops...)
+		flags = kv.ApplyFlagsOps(flags, ops...)
 	}
 	if flags.AndPersistent() != 0 {
 		db.dirty = true
 	}
-	x.setKeyFlags(flags)
+	x.resetKeyFlags(flags)
 
 	if value == nil {
 		return nil
@@ -847,18 +852,33 @@ func (n *memdbNode) getKey() []byte {
 
 const (
 	// bit 1 => red, bit 0 => black
-	nodeColorBit  uint16 = 0x8000
-	nodeFlagsMask        = ^nodeColorBit
+	nodeColorBit uint16 = 0x8000
+	// bit 1 => node is deleted, bit 0 => node is not deleted
+	// This flag is used to mark a node as deleted, so that we can reuse the node to avoid memory leak.
+	deleteFlag    uint16 = 1 << 14
+	nodeFlagsMask        = ^(nodeColorBit | deleteFlag)
 )
 
 func (n *memdbNode) getKeyFlags() kv.KeyFlags {
 	return kv.KeyFlags(n.flags & nodeFlagsMask)
 }
 
-func (n *memdbNode) setKeyFlags(f kv.KeyFlags) {
+func (n *memdbNode) resetKeyFlags(f kv.KeyFlags) {
 	n.flags = (^nodeFlagsMask & n.flags) | uint16(f)
 }
 
+func (n *memdbNode) markDelete() {
+	n.flags = (nodeColorBit & n.flags) | deleteFlag
+}
+
+func (n *memdbNode) unmarkDelete() {
+	n.flags &= ^deleteFlag
+}
+
+func (n *memdbNode) isDeleted() bool {
+	return n.flags&deleteFlag != 0
+}
+
 // RemoveFromBuffer removes a record from the mem buffer. It should be only used for test.
 func (db *MemDB) RemoveFromBuffer(key []byte) {
 	x := db.traverse(key, false)

internal/unionstore/memdb_arena.go

@@ -384,9 +384,11 @@ func (l *memdbVlog) revertToCheckpoint(db *MemDB, cp *MemDBCheckpoint) {
 			// If there are no flags associated with this key, we need to delete this node.
 			keptFlags := node.getKeyFlags().AndPersistent()
 			if keptFlags == 0 {
-				db.deleteNode(node)
+				node.markDelete()
+				db.count--
+				db.size -= int(node.klen)
 			} else {
-				node.setKeyFlags(keptFlags)
+				node.resetKeyFlags(keptFlags)
 				db.dirty = true
 			}
 		} else {

internal/unionstore/memdb_iterator.go

@@ -117,7 +117,7 @@ func (i *MemdbIterator) init() {
 		}
 	}
 
-	if i.isFlagsOnly() && !i.includeFlags {
+	if (i.isFlagsOnly() && !i.includeFlags) || (!i.curr.isNull() && i.curr.isDeleted()) {
 		err := i.Next()
 		_ = err // memdbIterator will never fail
 	}
@@ -140,7 +140,7 @@ func (i *MemdbIterator) Flags() kv.KeyFlags {
 func (i *MemdbIterator) UpdateFlags(ops ...kv.FlagsOp) {
 	origin := i.curr.getKeyFlags()
 	n := kv.ApplyFlagsOps(origin, ops...)
-	i.curr.setKeyFlags(n)
+	i.curr.resetKeyFlags(n)
 }
 
 // HasValue returns false if it is flags only.
@@ -175,6 +175,10 @@ func (i *MemdbIterator) Next() error {
 			i.curr = i.db.successor(i.curr)
 		}
 
+		if i.curr.isDeleted() {
+			continue
+		}
+
 		// We need to skip persistent flags only nodes.
 		if i.includeFlags || !i.isFlagsOnly() {
 			break
@@ -196,6 +200,9 @@ func (i *MemdbIterator) seekToFirst() {
 	}
 
 	i.curr = y
+	for !i.curr.isNull() && i.curr.isDeleted() {
+		i.curr = i.db.successor(i.curr)
+	}
 }
 
 func (i *MemdbIterator) seekToLast() {
@@ -208,6 +215,9 @@ func (i *MemdbIterator) seekToLast() {
 	}
 
 	i.curr = y
+	for !i.curr.isNull() && i.curr.isDeleted() {
+		i.curr = i.db.predecessor(i.curr)
+	}
 }
 
 func (i *MemdbIterator) seek(key []byte) {

internal/unionstore/memdb_test.go

@@ -39,6 +39,8 @@ package unionstore
 import (
 	"encoding/binary"
 	"fmt"
+	"strconv"
+	"strings"
 	"testing"
 
 	leveldb "github.com/pingcap/goleveldb/leveldb/memdb"
@@ -879,3 +881,23 @@ func TestSnapshotGetIter(t *testing.T) {
 		assert.Equal(iter.Value(), []byte{byte(50)})
 	}
 }
+
+func TestMemDBLeafFragmentation(t *testing.T) {
+	buffer := newMemDB()
+	assert := assert.New(t)
+	h := buffer.Staging()
+	mem := buffer.Mem()
+	for i := 0; i < 10; i++ {
+		for k := 0; k < 100; k++ {
+			buffer.Set([]byte(strings.Repeat(strconv.Itoa(k), 256)), []byte("value"))
+		}
+		cur := buffer.Mem()
+		if mem == 0 {
+			mem = cur
+		} else {
+			assert.LessOrEqual(cur, mem)
+		}
+		buffer.Cleanup(h)
+		h = buffer.Staging()
+	}
+}