[#9999] metabase: Fix db engine to pebble in children.go

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

pkg/local_object_storage/metabase/children.go

@@ -7,7 +7,7 @@ import (
 	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/internal/metaerr"
 	"git.frostfs.info/TrueCloudLab/frostfs-observability/tracing"
 	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
-	"go.etcd.io/bbolt"
+	"github.com/cockroachdb/pebble"
 	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/trace"
 )
@@ -37,34 +37,30 @@ func (db *DB) GetChildren(ctx context.Context, addresses []oid.Address) (map[oid
 	}
 
 	result := make(map[oid.Address][]oid.Address, len(addresses))
-
-	buffer := make([]byte, bucketKeySize)
-	err := db.database.View(func(tx *bbolt.Tx) error {
+	err := db.snapshot(func(s *pebble.Snapshot) error {
 		for _, addr := range addresses {
 			if _, found := result[addr]; found {
 				continue
 			}
 
 			result[addr] = []oid.Address{}
-			bkt := tx.Bucket(parentBucketName(addr.Container(), buffer))
-			if bkt == nil {
-				continue
-			}
 
-			binObjIDs, err := decodeList(bkt.Get(objectKey(addr.Object(), buffer)))
-			if err != nil {
-				return err
-			}
-
-			for _, binObjID := range binObjIDs {
-				var id oid.ID
-				if err = id.Decode(binObjID); err != nil {
+			for {
+				keys, err := selectByPrefixBatch(ctx, s, parentKeyLongPrefix(addr.Container(), addr.Object()), batchSize)
+				if err != nil {
 					return err
 				}
-				var resultAddress oid.Address
-				resultAddress.SetContainer(addr.Container())
-				resultAddress.SetObject(id)
-				result[addr] = append(result[addr], resultAddress)
+
+				for _, key := range keys {
+					resultAddress, err := addressOfTargetFromParentKey(key)
+					if err != nil {
+						return err
+					}
+					result[addr] = append(result[addr], resultAddress)
+				}
+				if len(keys) < batchSize {
+					break
+				}
 			}
 		}
 		return nil