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Revised migration context: don't store changerecord unless something was changed, and always snapshot if and after changes done.

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This commit is contained in:
LeoVasanko
2026-06-15 22:14:03 +00:00
parent c4726e6728
commit 42789e6619
6 changed files with 140 additions and 28 deletions
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kanta/kantaimpl.py
+31 -13
View File
@@ -110,6 +110,9 @@ class KantaImpl(PersistenceMixin, Generic[T]):
action="open",
)
# From this point the file is open and must be closed via close().
self.opened = True
if content:
try:
rr = replay(
@@ -140,12 +143,24 @@ class KantaImpl(PersistenceMixin, Generic[T]):
) from e
migrations_ran = False
state_before_migrations = None
if self.migrations is not None:
previous_version = rr.version
state_before_migrations = copy.deepcopy(rr.state)
rr.version = self.migrations.apply(rr.state, rr.version, self._kanta)
migrations_ran = rr.version != previous_version
self.statedict = copy.deepcopy(rr.state)
self.snapshot.ts = (
datetime.fromtimestamp(rr.last_snapshot_mtime, UTC)
if rr.last_snapshot_mtime is not None
else None
)
self.statedict = copy.deepcopy(
state_before_migrations
if state_before_migrations is not None
else rr.state
)
self.data = restore_data_in_place(
self.data,
rr.state,
@@ -158,20 +173,24 @@ class KantaImpl(PersistenceMixin, Generic[T]):
if self.readonly:
self.statedict = copy.deepcopy(normalized)
else:
if migrations_ran:
self.queue_change(
migration_record = None
if migrations_ran and self.statedict != rr.state:
migration_record = self.queue_change(
f"migrate:v{self.version}",
self.statedict,
rr.state,
mtime=False,
force=True,
)
self.queue_change("migrate:msgspec", normalized, mtime=False)
self.snapshot.ts = (
datetime.fromtimestamp(rr.last_snapshot_mtime, UTC)
if rr.last_snapshot_mtime is not None
else None
)
msgspec_record = self.queue_change(
"migrate:msgspec", normalized, mtime=False
)
if migrations_ran or msgspec_record is not None:
self.snapshot.request_force()
await self.flush()
self.snapshot.maybe_write(
self.file, self.version, self.statedict, m=self.mtime
)
elif self.readonly:
self.opened = False
self.file.close()
raise DataIntegrityError(
"Cannot open empty database in read-only mode",
@@ -196,6 +215,7 @@ class KantaImpl(PersistenceMixin, Generic[T]):
force=True,
)
except Exception:
self.opened = False
self.file.close()
try:
await asyncio.to_thread(self.filename.unlink, missing_ok=True)
@@ -203,8 +223,6 @@ class KantaImpl(PersistenceMixin, Generic[T]):
pass
raise
self.opened = True
if not self.readonly:
self.background_task = asyncio.create_task(self._background_loop())
kanta/snapshot.py
+8 -7
View File
@@ -41,15 +41,16 @@ class SnapshotState:
self, file, version: int, state: dict, m: datetime | None = None
) -> None:
"""Write snapshot when thresholds/time policy allows it."""
if self.changes < self._min_diffs:
return
force = self._force_pending
now = datetime.now(UTC)
if not force and now.weekday() != 6: # 6 = Sunday
return
sunday_midnight = now.replace(hour=0, minute=0, second=0, microsecond=0)
if not force and self.ts is not None and self.ts >= sunday_midnight:
return
if not force:
if self.changes < self._min_diffs:
return
if now.weekday() != 6: # 6 = Sunday
return
sunday_midnight = now.replace(hour=0, minute=0, second=0, microsecond=0)
if self.ts is not None and self.ts >= sunday_midnight:
return
if not file.is_open:
return
try:
kanta/structs.py
+1 -1
View File
@@ -23,7 +23,7 @@ class ChangeRecord(msgspec.Struct, omit_defaults=True, kw_only=True):
v: int = 0
u: str | None = None
m: datetime | None = None
diff: dict
diff: dict = {}
class Snapshot(msgspec.Struct, omit_defaults=True):
tests/support.py
+12 -1
View File
@@ -7,7 +7,7 @@ from uuid import UUID
import msgspec
from kanta.kanta import Kanta
from kanta.structs import ChangeRecord
from kanta.structs import ChangeRecord, Snapshot
class User(msgspec.Struct):
@@ -89,6 +89,17 @@ def make_migrations_module(name: str, fn_name: str, fn):
return mod
def read_last_snapshot(path: Path, format_config) -> Snapshot | None:
_, serializer_cls = format_config
serializer = serializer_cls()
framer = serializer.framer_cls()
data = path.read_bytes()
payload, _, _ = framer.scan_last_snapshot(data)
if payload is None:
return None
return serializer.decode(payload, type=Snapshot)
def fixed_change(action: str, diff: dict, *, version: int = 0) -> ChangeRecord:
return ChangeRecord(
ts=datetime(2026, 1, 1, tzinfo=UTC), a=action, v=version, diff=diff
tests/test_kanta_integration.py
+71 -6
View File
@@ -19,6 +19,7 @@ from .support import (
make_kanta,
make_migrations_module,
read_changes,
read_last_snapshot,
seed_single_change,
)
@@ -70,6 +71,27 @@ async def test_new_file_persists_initial_state_for_roundtrip(tmp_path, format_co
await kanta2.close()
@pytest.mark.asyncio
async def test_reopen_without_changes_does_not_force_snapshot(
tmp_path, format_config
):
path = tmp_path / "test.db"
kanta = make_kanta(path, Data(counter=5), format_config)
await kanta.open()
await kanta.close()
# No snapshot should exist after the initial bootstrap and close.
assert read_last_snapshot(path, format_config) is None
kanta2 = make_kanta(path, Data, format_config)
await kanta2.open()
assert kanta2.data.counter == 5
await kanta2.close()
# Re-opening without migrations or normalization changes must not force one.
assert read_last_snapshot(path, format_config) is None
@pytest.mark.asyncio
async def test_open_overwrites_caller_owned_root_data(tmp_path, format_config):
path = tmp_path / "test.db"
@@ -475,7 +497,9 @@ async def test_msgspec_normalization_logs_migration(tmp_path, format_config):
@pytest.mark.asyncio
async def test_empty_migration_is_recorded_and_not_reapplied(tmp_path, format_config):
async def test_empty_migration_writes_snapshot_and_is_not_reapplied(
tmp_path, format_config
):
path = tmp_path / "test.db"
seed_single_change(
path, fixed_change("init", {"counter": 0, "users": {}}), format_config
@@ -491,26 +515,67 @@ async def test_empty_migration_is_recorded_and_not_reapplied(tmp_path, format_co
kanta = make_kanta(path, Data, format_config, migrations=mod)
await kanta.open()
assert kanta.version == 1
await kanta.flush()
await kanta.close()
# Empty migrations must not produce empty change records.
records = read_changes(path, format_config)
migration_records = [r for r in records if r.a.startswith("migrate")]
assert len(migration_records) == 1
assert migration_records[0].v == 1
assert migration_records[0].diff == {}
assert not migration_records
# The version bump is persisted via a snapshot instead.
snap = read_last_snapshot(path, format_config)
assert snap is not None
assert snap.v == 1
assert snap.state == {"counter": 0, "users": {}}
kanta2 = make_kanta(path, Data, format_config, migrations=mod)
await kanta2.open()
assert kanta2.version == 1
await kanta2.close()
# Re-opening must not create additional migration records or snapshots.
records2 = read_changes(path, format_config)
assert len([r for r in records2 if r.a.startswith("migrate")]) == 1
assert not [r for r in records2 if r.a.startswith("migrate")]
finally:
sys.modules.pop("empty_migration_mod", None)
@pytest.mark.asyncio
async def test_migration_with_changes_records_diff_and_snapshot(
tmp_path, format_config
):
path = tmp_path / "test.db"
seed_single_change(path, fixed_change("init", {"counter": 0}), format_config)
mod = type(sys)("test_migrations_changes")
def migrate_v1(d, kanta):
d["counter"] = 2
mod.__dict__["migrate_v1"] = migrate_v1
kanta = make_kanta(path, Data, format_config, migrations=mod)
await kanta.open()
assert kanta.version == 1
assert kanta.data.counter == 2
await kanta.close()
records = read_changes(path, format_config)
migration_records = [r for r in records if r.a.startswith("migrate")]
assert len(migration_records) == 2
assert migration_records[0].a == "migrate:v1"
assert migration_records[0].v == 1
assert migration_records[0].diff == {"counter": 2}
assert migration_records[1].a == "migrate:msgspec"
assert migration_records[1].v == 1
assert migration_records[1].diff == {"users": {}}
snap = read_last_snapshot(path, format_config)
assert snap is not None
assert snap.v == 1
assert snap.state == {"counter": 2, "users": {}}
@pytest.mark.asyncio
async def test_open_locked_file_raises_filelock_error(tmp_path, format_config):
path = tmp_path / "test.db"
tests/test_snapshot.py
+17
View File
@@ -32,3 +32,20 @@ def test_force_writes():
f = FakeFile()
ss.maybe_write(f, 1, {"x": 1})
assert len(f.written) == 1
def test_force_bypasses_min_diffs():
class FakeFile:
def __init__(self):
self.written = []
self.is_open = True
def write(self, data: bytes):
self.written.append(data)
ss = SnapshotState(min_diffs=100)
ss.record_changes(5)
ss.request_force()
f = FakeFile()
ss.maybe_write(f, 1, {"x": 1})
assert len(f.written) == 1