[#948] metabase: Simplify cursor structure

Use bbolt bucket keys to seek offset in root bucket
and container buckets.

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

pkg/local_object_storage/metabase/list.go

@@ -1,15 +1,18 @@
 package meta
 
 import (
+	"strings"
+
 	core "github.com/nspcc-dev/neofs-node/pkg/core/object"
+	cid "github.com/nspcc-dev/neofs-sdk-go/container/id"
 	"github.com/nspcc-dev/neofs-sdk-go/object"
 	"go.etcd.io/bbolt"
 )
 
 // Cursor is a type for continuous object listing.
 type Cursor struct {
-	bucket  uint8
-	address *object.Address
+	bucketName     []byte
+	inBucketOffset []byte
 }
 
 // ListPrm contains parameters for ListWithCursor operation.
@@ -48,12 +51,6 @@ func (l ListRes) Cursor() *Cursor {
 	return l.cursor
 }
 
-const (
-	cursorBucketPrimary = iota
-	cursorBucketTombstone
-	cursorBucketSG
-)
-
 // ListWithCursor lists physical objects available in metabase starting from
 // cursor. Includes regular, tombstone and storage group objects. Does not
 // include inhumed objects. Use cursor value from response for consecutive requests.
@@ -88,55 +85,50 @@ func (db *DB) ListWithCursor(prm *ListPrm) (res *ListRes, err error) {
 func (db *DB) listWithCursor(tx *bbolt.Tx, count int, cursor *Cursor) ([]*object.Address, *Cursor, error) {
 	threshold := cursor == nil // threshold is a flag to ignore cursor
 	result := make([]*object.Address, 0, count)
-	unique := make(map[string]struct{}) // do not parse the same containerID twice
+	var bucketName []byte
 
 	c := tx.Cursor()
 	name, _ := c.First()
 
 	if !threshold {
-		name, _ = c.Seek([]byte(cursor.address.ContainerID().String()))
+		name, _ = c.Seek(cursor.bucketName)
 	}
 
 loop:
 	for ; name != nil; name, _ = c.Next() {
-		containerID := parseContainerID(name, unique)
+		containerID, postfix := parseContainerIDWithPostfix(name)
 		if containerID == nil {
 			continue
 		}
 
-		unique[containerID.String()] = struct{}{}
+		switch postfix {
+		case "", storageGroupPostfix, tombstonePostfix:
+		default:
+			continue
+		}
+
 		prefix := containerID.String() + "/"
 
-		lookupBuckets := [...]struct {
-			name   []byte
-			bucket uint8
-		}{
-			{primaryBucketName(containerID), cursorBucketPrimary},
-			{tombstoneBucketName(containerID), cursorBucketTombstone},
-			{storageGroupBucketName(containerID), cursorBucketSG},
+		result, cursor = selectNFromBucket(tx, name, prefix, result, count, cursor, threshold)
+		bucketName = name
+		if len(result) >= count {
+			break loop
 		}
 
-		for _, lb := range lookupBuckets {
-			if !threshold && cursor.bucket != lb.bucket {
-				continue // start from the bucket, specified in the cursor bucket
-			}
-
-			result, cursor = selectNFromBucket(tx, lb.name, prefix, result, count, cursor, threshold)
-			cursor.bucket = lb.bucket
-			if len(result) >= count {
-				break loop
-			}
-
-			// set threshold flag after first `selectNFromBucket` invocation
-			// first invocation must look for cursor object
-			threshold = true
-		}
+		// set threshold flag after first `selectNFromBucket` invocation
+		// first invocation must look for cursor object
+		threshold = true
 	}
 
 	if len(result) == 0 {
 		return nil, nil, core.ErrEndOfListing
 	}
 
+	// new slice is much faster but less memory efficient
+	// we need to copy, because bucketName exists during bbolt tx
+	cursor.bucketName = make([]byte, len(bucketName))
+	copy(cursor.bucketName, bucketName)
+
 	return result, cursor, nil
 }
 
@@ -163,8 +155,10 @@ func selectNFromBucket(tx *bbolt.Tx,
 	c := bkt.Cursor()
 	k, _ := c.First()
 
+	offset := cursor.inBucketOffset
+
 	if !threshold {
-		c.Seek([]byte(cursor.address.ObjectID().String()))
+		c.Seek(offset)
 		k, _ = c.Next() // we are looking for objects _after_ the cursor
 	}
 
@@ -176,7 +170,7 @@ func selectNFromBucket(tx *bbolt.Tx,
 		if err := a.Parse(prefix + string(k)); err != nil {
 			break
 		}
-		cursor.address = a
+		offset = k
 		if inGraveyard(tx, a) > 0 {
 			continue
 		}
@@ -184,5 +178,30 @@ func selectNFromBucket(tx *bbolt.Tx,
 		count++
 	}
 
+	// new slice is much faster but less memory efficient
+	// we need to copy, because offset exists during bbolt tx
+	cursor.inBucketOffset = make([]byte, len(offset))
+	copy(cursor.inBucketOffset, offset)
+
 	return to, cursor
 }
+
+func parseContainerIDWithPostfix(name []byte) (*cid.ID, string) {
+	var (
+		containerID    = cid.New()
+		containerIDStr = string(name)
+		postfix        string
+	)
+
+	ind := strings.Index(string(name), invalidBase58String)
+	if ind > 0 {
+		postfix = containerIDStr[ind:]
+		containerIDStr = containerIDStr[:ind]
+	}
+
+	if err := containerID.Parse(containerIDStr); err != nil {
+		return nil, ""
+	}
+
+	return containerID, postfix
+}