Introduce backup data formats for cross-version compatibility.

posting/list.go

@@ -1258,3 +1258,32 @@ func (l *List) PartSplits() []uint64 {
 	copy(splits, l.plist.Splits)
 	return splits
 }
+
+// ToBackupPostingList converts a posting list into its representation used for storing backups.
+func ToBackupPostingList(l *pb.PostingList) *pb.BackupPostingList {
+	bl := pb.BackupPostingList{}
+	if l == nil {
+		return &bl
+	}
+
+	bl.Uids = codec.Decode(l.Pack, 0)
+	bl.Postings = l.Postings
+	bl.CommitTs = l.CommitTs
+	bl.Splits = l.Splits
+	return &bl
+}
+
+// FromBackupPostingList converts a posting list in the format used for backups to a
+// normal posting list.
+func FromBackupPostingList(bl *pb.BackupPostingList) *pb.PostingList {
+	l := pb.PostingList{}
+	if bl == nil {
+		return &l
+	}
+
+	l.Pack = codec.Encode(bl.Uids, blockSize)
+	l.Postings = bl.Postings
+	l.CommitTs = bl.CommitTs
+	l.Splits = bl.Splits
+	return &l
+}

protos/pb.proto

@@ -499,4 +499,23 @@ message ExportRequest {
 	string  format   = 4;
 }
 
+// A key stored in the format used for writing backups.
+message BackupKey {
+  bytes byteType = 1;
+  string attr = 2;
+  uint64 uid = 3;
+  uint64 start_uid = 4;
+  string term = 5;
+  uint32 count = 6;
+  bytes byte_prefix = 7;
+}
+
+// A posting list stored in the format used for writing backups.
+message BackupPostingList {
+	repeated uint64 uids = 1;
+	repeated Posting postings = 2;
+	uint64 commit_ts = 3;
+  repeated uint64 splits = 4;
+}
+
 // vim: noexpandtab sw=2 ts=2