introduce parent snapshot id and revamp change data to depend on it (#63

)

This is for the introduction of the branching.

python/src/space/core/ops/change_data.py

@@ -58,29 +58,26 @@ def read_change_data(storage: Storage, start_snapshot_id: int,
   
   start_snapshot_id is excluded; end_snapshot_id is included.
   """
-  if start_snapshot_id > end_snapshot_id:
+  if start_snapshot_id >= end_snapshot_id:
     raise errors.UserInputError(
         f"End snapshot ID {end_snapshot_id} should not be lower than start "
         f"snapshot ID {start_snapshot_id}")
 
-  all_snapshot_ids = sorted(storage.snapshot_ids)
-  all_snapshot_ids_set = set(all_snapshot_ids)
-
-  if start_snapshot_id not in all_snapshot_ids_set:
-    raise errors.VersionNotFoundError(
-        f"Start snapshot ID not found: {start_snapshot_id}")
-
-  if end_snapshot_id not in all_snapshot_ids_set:
-    raise errors.VersionNotFoundError(
-        f"Start snapshot ID not found: {end_snapshot_id}")
+  all_snapshot_ids: List[int] = []
+  current_snapshot = storage.snapshot(end_snapshot_id)
+  while current_snapshot.snapshot_id >= start_snapshot_id:
+    all_snapshot_ids.insert(0, current_snapshot.snapshot_id)
+    if not current_snapshot.HasField("parent_snapshot_id"):
+      break
 
-  for snapshot_id in all_snapshot_ids:
-    if snapshot_id <= start_snapshot_id:
-      continue
+    current_snapshot = storage.snapshot(current_snapshot.parent_snapshot_id)
 
-    if snapshot_id > end_snapshot_id:
-      break
+  if start_snapshot_id != all_snapshot_ids[0]:
+    raise errors.UserInputError(
+        f"Start snapshot {start_snapshot_id} is not the  ancestor of "
+        f"end snapshot{end_snapshot_id}")
 
+  for snapshot_id in all_snapshot_ids[1:]:
     for result in iter(_LocalChangeDataReadOp(storage, snapshot_id)):
       yield result
 

python/src/space/core/proto/metadata.proto

@@ -84,7 +84,7 @@ message Schema {
 
 // Storage snapshot persisting physical metadata such as manifest file paths.
 // It is used for obtaining all alive data file paths for a given snapshot.
-// NEXT_ID: 6
+// NEXT_ID: 7
 message Snapshot {
   // The snapshot ID.
   int64 snapshot_id = 1;
@@ -104,6 +104,9 @@ message Snapshot {
 
   // File path of the change log of the snapshot.
   string change_log_file = 5;
+
+  // The snapshot ID of the parent snapshot.
+  optional int64 parent_snapshot_id = 6;
 }
 
 // Reference to a snapshot.

python/src/space/core/proto/metadata_pb2.pyi

@@ -209,7 +209,7 @@ global___Schema = Schema
 class Snapshot(google.protobuf.message.Message):
     """Storage snapshot persisting physical metadata such as manifest file paths.
     It is used for obtaining all alive data file paths for a given snapshot.
-    NEXT_ID: 6
+    NEXT_ID: 7
     """
 
     DESCRIPTOR: google.protobuf.descriptor.Descriptor
@@ -219,6 +219,7 @@ class Snapshot(google.protobuf.message.Message):
     MANIFEST_FILES_FIELD_NUMBER: builtins.int
     STORAGE_STATISTICS_FIELD_NUMBER: builtins.int
     CHANGE_LOG_FILE_FIELD_NUMBER: builtins.int
+    PARENT_SNAPSHOT_ID_FIELD_NUMBER: builtins.int
     snapshot_id: builtins.int
     """The snapshot ID."""
     @property
@@ -234,6 +235,8 @@ class Snapshot(google.protobuf.message.Message):
         """Statistics of all data in the storage."""
     change_log_file: builtins.str
     """File path of the change log of the snapshot."""
+    parent_snapshot_id: builtins.int
+    """The snapshot ID of the parent snapshot."""
     def __init__(
         self,
         *,
@@ -242,9 +245,13 @@ class Snapshot(google.protobuf.message.Message):
         manifest_files: global___ManifestFiles | None = ...,
         storage_statistics: global___StorageStatistics | None = ...,
         change_log_file: builtins.str = ...,
+        parent_snapshot_id: builtins.int | None = ...,
     ) -> None: ...
-    def HasField(self, field_name: typing_extensions.Literal["create_time", b"create_time", "data_info", b"data_info", "manifest_files", b"manifest_files", "storage_statistics", b"storage_statistics"]) -> builtins.bool: ...
-    def ClearField(self, field_name: typing_extensions.Literal["change_log_file", b"change_log_file", "create_time", b"create_time", "data_info", b"data_info", "manifest_files", b"manifest_files", "snapshot_id", b"snapshot_id", "storage_statistics", b"storage_statistics"]) -> None: ...
+    def HasField(self, field_name: typing_extensions.Literal["_parent_snapshot_id", b"_parent_snapshot_id", "create_time", b"create_time", "data_info", b"data_info", "manifest_files", b"manifest_files", "parent_snapshot_id", b"parent_snapshot_id", "storage_statistics", b"storage_statistics"]) -> builtins.bool: ...
+    def ClearField(self, field_name: typing_extensions.Literal["_parent_snapshot_id", b"_parent_snapshot_id", "change_log_file", b"change_log_file", "create_time", b"create_time", "data_info", b"data_info", "manifest_files", b"manifest_files", "parent_snapshot_id", b"parent_snapshot_id", "snapshot_id", b"snapshot_id", "storage_statistics", b"storage_statistics"]) -> None: ...
+    @typing.overload
+    def WhichOneof(self, oneof_group: typing_extensions.Literal["_parent_snapshot_id", b"_parent_snapshot_id"]) -> typing_extensions.Literal["parent_snapshot_id"] | None: ...
+    @typing.overload
     def WhichOneof(self, oneof_group: typing_extensions.Literal["data_info", b"data_info"]) -> typing_extensions.Literal["manifest_files"] | None: ...
 
 global___Snapshot = Snapshot

python/src/space/core/storage.py

@@ -268,7 +268,8 @@ def commit(self, patch: rt.Patch) -> None:
         snapshot_id=new_snapshot_id,
         create_time=proto_now(),
         manifest_files=current_snapshot.manifest_files,
-        storage_statistics=current_snapshot.storage_statistics)
+        storage_statistics=current_snapshot.storage_statistics,
+        parent_snapshot_id=current_snapshot.snapshot_id)
     _patch_manifests(snapshot.manifest_files, patch)
 
     if patch.HasField('change_log'):