Add kanta.bootstrap logger and configurable logging setup

- Bootstrap records are now logged via kanta.bootstrap at INFO level.
- Existing databases log 'Using <path>' at DEBUG on kanta.bootstrap.
- New databases log 'Created <path>' at INFO on kanta.bootstrap.
- Renamed loggers: kanta.changes -> kanta.transaction, kanta.migrations -> kanta.migration.
- configure_logging() gains bootstrap/migration/transaction/skiproot kwargs.
- Default configure_logging() attaches a no-prefix stderr handler to kanta and stops propagation.
- With skiproot=False, child logger propagation flags are still applied but kanta itself is left untouched.
- Updated tests and docstrings.

kanta/callbacks.py

@@ -18,6 +18,7 @@ from dataclasses import dataclass
 from typing import Annotated, Any, Union, get_args, get_origin
 
 from kanta.exceptions import DatabaseError
+from kanta.migrations import MigrationResult
 
 DictPre = Annotated[dict, "pre"]
 DictPost = Annotated[dict, "post"]
@@ -59,6 +60,7 @@ class InjectionContext:
     error: DatabaseError | None = None
     previous_state: dict | None = None
     current_state: dict | None = None
+    migration_result: MigrationResult | None = None
 
 
 @dataclass
@@ -98,6 +100,7 @@ class CallbackRegistry:
         self._callbacks: dict[str, list[_CallbackRegistration]] = {
             "bootstrap": [],
             "fatal_error": [],
+            "logmigr": [],
         }
         self._logfmt_callbacks: list[_LogFmtFunctionSpec | _LogFmtClassSpec] = []
 
@@ -446,10 +449,12 @@ class CallbackRegistry:
             return kind == "logfmt"
         if bare is DatabaseError:
             return kind == "fatal_error"
+        if bare is MigrationResult:
+            return kind == "logmigr"
         if self._data_type is not None and bare is self._data_type:
             return kind == "bootstrap"
         if self._kanta_class is not None and bare is self._kanta_class:
-            return kind in {"bootstrap", "fatal_error", "logfmt"}
+            return kind in {"bootstrap", "fatal_error", "logfmt", "logmigr"}
         return False
 
     def _allowed_message(self, kind: str) -> str:
@@ -462,6 +467,8 @@ class CallbackRegistry:
                 parts.append(self._kanta_class.__name__)
         if kind == "fatal_error":
             parts.append("DatabaseError")
+        if kind == "logmigr":
+            parts.append("MigrationResult")
         if kind == "logfmt":
             parts.append("Annotated[dict, 'pre']")
             parts.append("Annotated[dict, 'post']")
@@ -475,6 +482,8 @@ class CallbackRegistry:
             return ctx.current_state
         if bare is DatabaseError:
             return ctx.error
+        if bare is MigrationResult:
+            return ctx.migration_result
         if self._data_type is not None and bare is self._data_type:
             return ctx.data
         if self._kanta_class is not None and bare is self._kanta_class:

kanta/kanta.py

@@ -1,6 +1,7 @@
 """Kanta DB main public API"""
 
 from __future__ import annotations
+import logging
 from datetime import datetime
 from pathlib import Path
 from types import ModuleType, SimpleNamespace
@@ -144,7 +145,13 @@ class Kanta(Generic[T]):
         """
         return self._impl.mtime
 
-    async def open(self, *, create: bool = True, readonly: bool = False) -> None:
+    async def open(
+        self,
+        *,
+        create: bool = True,
+        readonly: bool = False,
+        log: bool | logging.Logger = True,
+    ) -> None:
         """Open the database file and start background persistence.
 
         This loads existing records, applies configured migrations, and starts
@@ -156,6 +163,13 @@ class Kanta(Generic[T]):
             readonly: If True, open the database read-only. No lock is acquired,
                 no background flush task is started, and transactions are
                 rejected. The file is not created if missing.
+            log: Controls bootstrap and migration logging. ``True`` (default)
+                uses the ``kanta.bootstrap`` logger for bootstrap records and
+                the ``kanta.migration`` logger for migration output. ``False``
+                suppresses the default bootstrap and migration logs. A
+                :class:`~logging.Logger` instance writes default output to that
+                logger instead. Custom ``@kanta.logmigr`` callbacks run
+                regardless of this setting.
 
         Calling ``open`` more than once on the same instance is not allowed.
 
@@ -163,7 +177,7 @@ class Kanta(Generic[T]):
             kanta.exceptions.DatabaseError: If replay or decoding fails.
             kanta.exceptions.DataIntegrityError: If the instance is already open.
         """
-        await self._impl.open(create=create, readonly=readonly)
+        await self._impl.open(create=create, readonly=readonly, log=log)
 
     async def __aenter__(self) -> Kanta[T]:
         """Enter async context manager and open the database.
@@ -239,6 +253,24 @@ class Kanta(Generic[T]):
             return _register
         return _register(fn)
 
+    def logmigr(self, fn=None):
+        """Register a migration logging callback.
+
+        Can be used as ``@kanta.logmigr``.
+        The callback receives a :class:`kanta.migrations.MigrationResult` and
+        may be sync or async. If registered, it replaces the default migration
+        logger output; the application is responsible for emitting any log
+        messages.
+        """
+
+        def _register(callback):
+            self._impl.add_logmigr(callback)
+            return callback
+
+        if fn is None:
+            return _register
+        return _register(fn)
+
     def logfmt(self, fn=None, *, path: str | None = None):
         """Register a transaction logfmt callback.
 
@@ -266,6 +298,7 @@ class Kanta(Generic[T]):
         *,
         user: str | None = None,
         mtime: bool | datetime = True,
+        log: bool | logging.Logger = True,
     ):
         """Create a transactional mutation context manager.
 
@@ -280,6 +313,10 @@ class Kanta(Generic[T]):
                 system operations that are not considered modifications. A
                 :class:`~datetime.datetime` value sets ``m`` to that explicit
                 time.
+            log: Controls transaction logging. ``True`` (default) uses the
+                ``kanta.transaction`` logger. ``False`` suppresses the
+                transaction log. A :class:`~logging.Logger` instance writes
+                output to that logger instead.
 
         Returns:
             A context manager yielding the live state object for mutation.
@@ -294,4 +331,5 @@ class Kanta(Generic[T]):
             action,
             user=user,
             mtime=mtime,
+            log=log,
         )

kanta/kantaimpl.py

@@ -12,7 +12,8 @@ from typing import Any, Generic, TypeVar
 
 from kanta.callbacks import CallbackRegistry, InjectionContext
 from kanta.exceptions import DatabaseError, DataIntegrityError, ReplayError
-from kanta.migrations import Migrations
+from kanta.logging import _USER_PATH, bootstrap_logger, log_change, migration_logger
+from kanta.migrations import MigrationResult, Migrations
 from kanta.persistence import PersistenceMixin
 from kanta.serialization import restore_data_in_place, struct_to_dict
 from kanta.serialization.base import replay
@@ -75,7 +76,64 @@ class KantaImpl(PersistenceMixin, Generic[T]):
         """Register one transaction logfmt callback."""
         self.callback_registry.register("logfmt", callback, path=path)
 
-    async def open(self, *, create: bool = True, readonly: bool = False) -> None:
+    def add_logmigr(self, callback) -> None:
+        """Register one migration logging callback."""
+        self.callback_registry.register("logmigr", callback)
+
+    async def _handle_migration_log(
+        self,
+        migration_result: MigrationResult,
+        previous_version: int,
+        log: bool | logging.Logger,
+    ) -> None:
+        """Route migration logging to callback or default logger."""
+        assert isinstance(migration_result, MigrationResult)
+
+        if self.callback_registry.has("logmigr"):
+            await self.callback_registry.invoke(
+                "logmigr",
+                InjectionContext(
+                    kanta=self._kanta,
+                    migration_result=migration_result,
+                ),
+            )
+            return
+
+        if log is False:
+            return
+
+        migration_log = log if isinstance(log, logging.Logger) else migration_logger
+
+        changed = [m for m in migration_result.migrations if m.changed]
+        if not changed:
+            return
+
+        for info in changed:
+            if info.diff:
+                log_change(
+                    info.name,
+                    info.diff,
+                    previous=info.before,
+                    logger=migration_log,
+                    level=logging.DEBUG,
+                )
+
+        descriptions = [f"{m.name} ({m.description})" for m in changed]
+        migration_log.info(
+            "Migrated %s v%s -> v%s: %s",
+            self.filename,
+            previous_version,
+            migration_result.version,
+            ", ".join(descriptions),
+        )
+
+    async def open(
+        self,
+        *,
+        create: bool = True,
+        readonly: bool = False,
+        log: bool | logging.Logger = True,
+    ) -> None:
         """Open the database: load from disk, apply migrations, start background task."""
         if self.opened:
             raise DataIntegrityError(
@@ -110,6 +168,9 @@ 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(
@@ -139,13 +200,33 @@ class KantaImpl(PersistenceMixin, Generic[T]):
                     cause_type=type(e).__name__,
                 ) from e
 
-            migrations_ran = False
+            migration_result = None
+            state_before_migrations = None
+            previous_version = rr.version
             if self.migrations is not None:
-                previous_version = rr.version
-                rr.version = self.migrations.apply(rr.state, rr.version, self._kanta)
-                migrations_ran = rr.version != previous_version
+                state_before_migrations = copy.deepcopy(rr.state)
+                migration_result = self.migrations.apply(
+                    rr.state, rr.version, self._kanta
+                )
+                rr.version = migration_result.version
 
-            self.statedict = copy.deepcopy(rr.state)
+            migrations_ran = rr.version != previous_version
+            migration_state_changed = (
+                state_before_migrations is not None
+                and state_before_migrations != 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,
@@ -154,24 +235,35 @@ class KantaImpl(PersistenceMixin, Generic[T]):
             )
             self.version = rr.version
             self.mtime = rr.m
+            if log is not False:
+                logger = log if isinstance(log, logging.Logger) else bootstrap_logger
+                logger.debug("Using %s", self.filename.resolve())
             normalized = struct_to_dict(self.data, serializer=self.serializer)
             if self.readonly:
                 self.statedict = copy.deepcopy(normalized)
             else:
-                if migrations_ran:
+                if migrations_ran and migration_state_changed:
                     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
+                    )
+
+                if migrations_ran and migration_result is not None:
+                    await self._handle_migration_log(
+                        migration_result, previous_version, log
+                    )
         elif self.readonly:
+            self.opened = False
             self.file.close()
             raise DataIntegrityError(
                 "Cannot open empty database in read-only mode",
@@ -188,14 +280,40 @@ class KantaImpl(PersistenceMixin, Generic[T]):
 
                 self.statedict = {}
                 current = struct_to_dict(self.data, serializer=self.serializer)
-                self.queue_change(
+                record = self.queue_change(
                     self.bootstrap_action,
                     current,
                     user=self.bootstrap_user,
                     mtime=self.bootstrap_mtime,
                     force=True,
                 )
+
+                if record is not None and log is not False:
+                    logger = log if isinstance(log, logging.Logger) else bootstrap_logger
+                    logger.info("Created %s", self.filename.resolve())
+                    logfmt = self.callback_registry.build_logfmt(
+                        InjectionContext(
+                            previous_state={},
+                            current_state=current,
+                            kanta=self._kanta,
+                        )
+                    )
+                    formatted_user = self.bootstrap_user
+                    if formatted_user is not None and logfmt is not None:
+                        resolved = logfmt(formatted_user, _USER_PATH)
+                        if resolved is not None:
+                            formatted_user = resolved
+                    log_change(
+                        self.bootstrap_action,
+                        record.diff,
+                        formatted_user,
+                        previous={},
+                        logfmt=logfmt,
+                        logger=logger,
+                        level=logging.INFO,
+                    )
             except Exception:
+                self.opened = False
                 self.file.close()
                 try:
                     await asyncio.to_thread(self.filename.unlink, missing_ok=True)
@@ -203,8 +321,6 @@ class KantaImpl(PersistenceMixin, Generic[T]):
                     pass
                 raise
 
-        self.opened = True
-
         if not self.readonly:
             self.background_task = asyncio.create_task(self._background_loop())
 

kanta/logging.py

@@ -1,7 +1,8 @@
 """Database change logging with pretty-printed diffs.
 
-Provides a logger for JSONL database changes that formats diffs
-in a human-readable path.notation style with color coding.
+Provides loggers for JSONL database changes, bootstrap events, and
+migrations.  Diff output is formatted in a human-readable path notation
+style with color coding.
 """
 
 import logging
@@ -10,7 +11,9 @@ import sys
 from collections.abc import Callable
 from typing import Any
 
-logger = logging.getLogger("kanta.changes")
+transaction_logger = logging.getLogger("kanta.transaction")
+bootstrap_logger = logging.getLogger("kanta.bootstrap")
+migration_logger = logging.getLogger("kanta.migration")
 
 # Pattern to match control characters and bidirectional overrides
 _UNSAFE_CHARS = re.compile(
@@ -274,6 +277,9 @@ def log_change(
     user: str | None = None,
     previous: dict | None = None,
     logfmt: Callable[[Any, str], str | None] | None = None,
+    *,
+    logger: logging.Logger = transaction_logger,
+    level: int = logging.INFO,
 ) -> None:
     """Log a database change with pretty-printed diff.
 
@@ -283,27 +289,63 @@ def log_change(
         user: Optional already-formatted user name to show in the header.
         previous: The previous state dict (for determining add vs update).
         logfmt: Optional formatter callable ``(value, path) -> str | None``.
+        logger: Logger to write to. Defaults to the ``kanta.transaction`` logger.
+        level: Log level to use. Defaults to ``logging.INFO``.
     """
     header = format_action_header(action, user)
     diff_lines = format_diff(diff, previous, logfmt)
 
     if not diff_lines:
-        logger.info(header)
+        logger.log(level, header)
         return
 
     if len(diff_lines) == 1:
-        logger.info(f"{header}{diff_lines[0]}")
+        logger.log(level, f"{header}{diff_lines[0]}")
     else:
-        logger.info(header)
+        logger.log(level, header)
         for line in diff_lines:
-            logger.info(line)
+            logger.log(level, line)
 
 
-def configure_logging() -> None:
-    """Configure the database logger to output to stderr without prefix."""
-    if not logger.handlers:
+def configure_logging(
+    *,
+    skiproot: bool = True,
+    bootstrap: bool = True,
+    migration: bool = True,
+    transaction: bool = True,
+) -> None:
+    """Configure Kanta's default logging output.
+
+    Args:
+        skiproot: If ``True`` (default), attach a no-prefix stderr handler to
+            the ``kanta`` logger and set ``kanta.propagate = False`` so Kanta
+            output is rendered directly without propagating to the root logger.
+            If ``False``, the child logger enable flags are still applied, but
+            no handler is added and ``kanta`` propagation is left untouched so
+            the application's root logger handles Kanta output.
+        bootstrap: Whether bootstrap logs are enabled.
+        migration: Whether migration logs are enabled.
+        transaction: Whether transaction logs are enabled.
+
+    This helper is not called automatically; applications that want Kanta's
+    default output can call it, but most applications will configure logging
+    themselves.
+    """
+    for name, enabled in (
+        ("kanta.bootstrap", bootstrap),
+        ("kanta.migration", migration),
+        ("kanta.transaction", transaction),
+    ):
+        logging.getLogger(name).propagate = enabled
+
+    if not skiproot:
+        return
+
+    target = logging.getLogger("kanta")
+    target.propagate = False
+
+    if not target.handlers:
         handler = logging.StreamHandler(sys.stderr)
         handler.setFormatter(logging.Formatter("%(message)s"))
-        logger.addHandler(handler)
-    logger.setLevel(logging.INFO)
-    logger.propagate = False
+        target.addHandler(handler)
+    target.setLevel(logging.INFO)

kanta/migrations.py

@@ -9,19 +9,38 @@ from __future__ import annotations
 import copy
 import importlib
 import inspect
-import logging
+from dataclasses import dataclass
 from types import ModuleType
 from typing import Any
 
+from kanta.diff import compute_diff
 from kanta.exceptions import DatabaseError
 
-_logger = logging.getLogger(__name__)
-
 # Cache registries by imported module object so that many Kanta instances using
 # the same migrations module do not re-scan it each time.
 _module_registry_cache: dict[ModuleType, Migrations] = {}
 
 
+@dataclass
+class MigrationInfo:
+    """Information about a single migration that ran."""
+
+    name: str
+    description: str
+    version: int
+    changed: bool
+    diff: dict | None = None
+    before: dict | None = None
+
+
+@dataclass
+class MigrationResult:
+    """Result of applying migrations."""
+
+    version: int
+    migrations: list[MigrationInfo]
+
+
 class Migrations:
     """Registry of schema migration functions.
 
@@ -38,12 +57,13 @@ class Migrations:
         def migrate_v2(d: dict) -> None:
             d.setdefault("version", 2)
 
-        new_version = migrations.apply(state, current_version=0, kanta=kanta)
+        result = migrations.apply(state, current_version=0, kanta=kanta)
+        new_version = result.version
 
     Or load from a module::
 
         migrations = Migrations.from_module("myapp.migrations")
-        new_version = migrations.apply(state, current_version=0, kanta=kanta)
+        result = migrations.apply(state, current_version=0, kanta=kanta)
     """
 
     def __init__(self) -> None:
@@ -117,9 +137,7 @@ class Migrations:
         data_dict: dict[str, Any],
         current_version: int,
         kanta: Any,
-        *,
-        silent: bool = False,
-    ) -> int:
+    ) -> MigrationResult:
         """Apply pending migrations to *data_dict* in place.
 
         Missing intermediate migration steps are silently skipped.
@@ -128,7 +146,8 @@ class Migrations:
             DatabaseError: If the database version is newer than the highest
                 supported version or older than the minimum supported version.
 
-        Returns the new version after all migrations.
+        Returns a :class:`MigrationResult` describing the new version and every
+        migration that ran.
         """
         if current_version > self.dbver:
             raise DatabaseError(
@@ -141,14 +160,25 @@ class Migrations:
                 f"minimum supported version v{self.minver}"
             )
 
+        migrations: list[MigrationInfo] = []
         for version in sorted(self._migrations.keys()):
             if version <= current_version:
                 continue
             fn = self._migrations[version]
-            before = copy.deepcopy(data_dict) if not silent else None
+            before = copy.deepcopy(data_dict)
             self._call_migration(fn, data_dict, kanta)
             current_version = version
-            if not silent and before != data_dict:
-                desc = (fn.__doc__ or fn.__name__).split("\n")[0].rstrip(".")
-                _logger.info("Applied migration %s: %s", fn.__name__, desc)
-        return current_version
+            changed = before != data_dict
+            diff = compute_diff(before, data_dict) if changed else None
+            desc = (fn.__doc__ or f"v{version}").split("\n")[0].rstrip(".")
+            migrations.append(
+                MigrationInfo(
+                    name=fn.__name__,
+                    description=desc,
+                    version=version,
+                    changed=changed,
+                    diff=diff,
+                    before=before,
+                )
+            )
+        return MigrationResult(version=current_version, migrations=migrations)

kanta/snapshot.py

@@ -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

@@ -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):

kanta/transaction.py

@@ -9,7 +9,7 @@ from datetime import datetime
 from kanta.diff import compute_diff
 from kanta.exceptions import DataIntegrityError
 from kanta.callbacks import InjectionContext
-from kanta.logging import _USER_PATH, log_change
+from kanta.logging import _USER_PATH, log_change, transaction_logger
 from kanta.serialization import restore_data_in_place, struct_to_dict
 
 _logger = logging.getLogger(__name__)
@@ -22,6 +22,7 @@ def transaction(
     *,
     user: str | None = None,
     mtime: bool | datetime = True,
+    log: bool | logging.Logger = True,
 ):
     """Wrap writes in a transaction and yield the live db object."""
     if impl.readonly:
@@ -80,7 +81,16 @@ def transaction(
                     resolved = logfmt(user, _USER_PATH)
                     if resolved is not None:
                         formatted_user = resolved
-                log_change(action, record.diff, formatted_user, previous, logfmt)
+                if log is not False:
+                    logger = log if isinstance(log, logging.Logger) else transaction_logger
+                    log_change(
+                        action,
+                        record.diff,
+                        formatted_user,
+                        previous,
+                        logfmt,
+                        logger=logger,
+                    )
     except Exception:
         _logger.warning("Transaction '%s' failed, rolling back changes", action)
         if impl.transaction_snapshot is not None:

tests/support.py

@@ -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_callbacks.py

@@ -148,7 +148,7 @@ async def test_bootstrap_injects_kanta(tmp_path, format_config):
 async def test_logfmt_injects_states(tmp_path, format_config, caplog):
     import logging
 
-    caplog.set_level(logging.INFO, logger="kanta.changes")
+    caplog.set_level(logging.INFO, logger="kanta.transaction")
     path = tmp_path / "test.db"
     kanta = make_kanta(path, Data, format_config)
 
@@ -170,13 +170,15 @@ async def test_logfmt_injects_states(tmp_path, format_config, caplog):
 async def test_logfmt_class_injection(tmp_path, format_config, caplog):
     import logging
 
-    caplog.set_level(logging.INFO, logger="kanta.changes")
+    caplog.set_level(logging.INFO, logger="kanta.transaction")
     path = tmp_path / "test.db"
     kanta = make_kanta(path, Data, format_config)
 
     @kanta.logfmt
     class UserLogFmt(LogFmt):
         def resolve(self, value: str, path: str) -> str | None:
+            if not isinstance(value, str):
+                return None
             return self.current_state.get("users", {}).get(value, {}).get("name")
 
     await kanta.open()
@@ -193,7 +195,7 @@ async def test_logfmt_class_injection(tmp_path, format_config, caplog):
 async def test_multiple_logfmt_chain(tmp_path, format_config, caplog):
     import logging
 
-    caplog.set_level(logging.INFO, logger="kanta.changes")
+    caplog.set_level(logging.INFO, logger="kanta.transaction")
     path = tmp_path / "test.db"
     kanta = make_kanta(path, Data, format_config)
 
@@ -221,7 +223,7 @@ async def test_multiple_logfmt_chain(tmp_path, format_config, caplog):
 async def test_logfmt_path_context(tmp_path, format_config, caplog):
     import logging
 
-    caplog.set_level(logging.INFO, logger="kanta.changes")
+    caplog.set_level(logging.INFO, logger="kanta.transaction")
     path = tmp_path / "test.db"
     kanta = make_kanta(path, Data, format_config)
 
@@ -245,7 +247,7 @@ async def test_logfmt_path_context(tmp_path, format_config, caplog):
 async def test_logfmt_decorator_path_filters_calls(tmp_path, format_config, caplog):
     import logging
 
-    caplog.set_level(logging.INFO, logger="kanta.changes")
+    caplog.set_level(logging.INFO, logger="kanta.transaction")
     path = tmp_path / "test.db"
     kanta = make_kanta(path, Data, format_config)
 
@@ -271,7 +273,7 @@ async def test_logfmt_decorator_path_filters_calls(tmp_path, format_config, capl
 async def test_logfmt_user_path_replaces_user_display(tmp_path, format_config, caplog):
     import logging
 
-    caplog.set_level(logging.INFO, logger="kanta.changes")
+    caplog.set_level(logging.INFO, logger="kanta.transaction")
     path = tmp_path / "test.db"
     kanta = make_kanta(path, Data, format_config)
 
@@ -293,7 +295,7 @@ async def test_logfmt_user_path_replaces_user_display(tmp_path, format_config, c
 async def test_logfmt_non_string_value(tmp_path, format_config, caplog):
     import logging
 
-    caplog.set_level(logging.INFO, logger="kanta.changes")
+    caplog.set_level(logging.INFO, logger="kanta.transaction")
     path = tmp_path / "test.db"
     kanta = make_kanta(path, Data, format_config)
 

tests/test_kanta_integration.py

@@ -1,4 +1,5 @@
 import asyncio
+import logging
 import sys
 from datetime import UTC, datetime
 from uuid import uuid4
@@ -6,6 +7,7 @@ from uuid import uuid4
 import pytest
 
 from kanta.exceptions import DatabaseError, DataIntegrityError, FileLockError
+from kanta.migrations import MigrationResult
 from kanta.serialization import struct_to_dict
 
 from .support import (
@@ -19,6 +21,7 @@ from .support import (
     make_kanta,
     make_migrations_module,
     read_changes,
+    read_last_snapshot,
     seed_single_change,
 )
 
@@ -70,6 +73,25 @@ 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 +515,249 @@ 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_migration_summary_log_includes_filename(tmp_path, format_config, caplog):
+    path = tmp_path / "test.db"
+    seed_single_change(path, fixed_change("init", {"counter": 0}), format_config)
+
+    mod = type(sys)("test_migrations_log")
+
+    def migrate_v1(d, kanta):
+        """Bump counter."""
+        d["counter"] = 2
+
+    mod.__dict__["migrate_v1"] = migrate_v1
+
+    with caplog.at_level(logging.INFO, logger="kanta.migration"):
+        kanta = make_kanta(path, Data, format_config, migrations=mod)
+        await kanta.open()
+        assert kanta.version == 1
+        await kanta.close()
+
+    info_messages = [r.message for r in caplog.records if r.levelno == logging.INFO]
+    assert len(info_messages) == 1
+    assert str(path) in info_messages[0]
+    assert "v0 -> v1" in info_messages[0]
+    assert "migrate_v1 (Bump counter)" in info_messages[0]
+
+
+@pytest.mark.asyncio
+async def test_open_log_false_suppresses_migration_log(tmp_path, format_config, caplog):
+    path = tmp_path / "test.db"
+    seed_single_change(path, fixed_change("init", {"counter": 0}), format_config)
+
+    mod = type(sys)("test_migrations_silent")
+
+    def migrate_v1(d, kanta):
+        d["counter"] = 2
+
+    mod.__dict__["migrate_v1"] = migrate_v1
+
+    with caplog.at_level(logging.INFO, logger="kanta.migration"):
+        kanta = make_kanta(path, Data, format_config, migrations=mod)
+        await kanta.open(log=False)
+        await kanta.close()
+
+    info_messages = [r for r in caplog.records if r.levelno == logging.INFO]
+    assert not info_messages
+
+
+@pytest.mark.asyncio
+async def test_open_log_true_logs_bootstrap(tmp_path, format_config, caplog):
+    path = tmp_path / "test.db"
+    kanta = make_kanta(path, Data, format_config)
+
+    with caplog.at_level(logging.INFO, logger="kanta.bootstrap"):
+        await kanta.open()
+        await kanta.close()
+
+    info_messages = [r.message for r in caplog.records if r.levelno == logging.INFO]
+    assert len(info_messages) >= 2
+    assert "Created" in info_messages[0]
+    assert "bootstrap" in info_messages[1]
+
+
+@pytest.mark.asyncio
+async def test_open_log_false_suppresses_bootstrap_log(tmp_path, format_config, caplog):
+    path = tmp_path / "test.db"
+    kanta = make_kanta(path, Data, format_config)
+
+    with caplog.at_level(logging.INFO, logger="kanta.bootstrap"):
+        await kanta.open(log=False)
+        await kanta.close()
+
+    info_messages = [r for r in caplog.records if r.levelno == logging.INFO]
+    assert not info_messages
+
+
+@pytest.mark.asyncio
+async def test_open_log_custom_logger_logs_bootstrap(tmp_path, format_config, caplog):
+    path = tmp_path / "test.db"
+    kanta = make_kanta(path, Data, format_config)
+
+    custom_logger = logging.getLogger("custom.bootstrap")
+    custom_logger.setLevel(logging.INFO)
+
+    with caplog.at_level(logging.INFO, logger="custom.bootstrap"):
+        await kanta.open(log=custom_logger)
+        await kanta.close()
+
+    info_messages = [r.message for r in caplog.records if r.levelno == logging.INFO]
+    assert len(info_messages) >= 2
+    assert "Created" in info_messages[0]
+    assert "bootstrap" in info_messages[1]
+
+
+@pytest.mark.asyncio
+async def test_open_existing_database_logs_using_on_debug(
+    tmp_path, format_config, caplog
+):
+    path = tmp_path / "test.db"
+    kanta = make_kanta(path, Data, format_config)
+    await kanta.open()
+    await kanta.close()
+
+    kanta2 = make_kanta(path, Data, format_config)
+
+    with caplog.at_level(logging.DEBUG, logger="kanta.bootstrap"):
+        await kanta2.open()
+        await kanta2.close()
+
+    debug_messages = [r.message for r in caplog.records if r.levelno == logging.DEBUG]
+    assert any("Using" in m and str(path.resolve()) in m for m in debug_messages)
+
+
+@pytest.mark.asyncio
+async def test_logmigr_callback_replaces_default_logging(
+    tmp_path, format_config, caplog
+):
+    path = tmp_path / "test.db"
+    seed_single_change(path, fixed_change("init", {"counter": 0}), format_config)
+
+    mod = type(sys)("test_migrations_callback")
+
+    def migrate_v1(d, kanta):
+        """Bump counter."""
+        d["counter"] = 2
+
+    mod.__dict__["migrate_v1"] = migrate_v1
+
+    summaries = []
+
+    kanta = make_kanta(path, Data, format_config, migrations=mod)
+
+    @kanta.logmigr
+    def collect(summary: MigrationResult):
+        summaries.append(summary)
+
+    with caplog.at_level(logging.INFO, logger="kanta.migration"):
+        await kanta.open()
+        await kanta.close()
+
+    assert len(summaries) == 1
+    assert summaries[0].version == 1
+    assert summaries[0].migrations[0].name == "migrate_v1"
+    info_messages = [r for r in caplog.records if r.levelno == logging.INFO]
+    assert not info_messages
+
+
+@pytest.mark.asyncio
+async def test_transaction_log_false_suppresses_log(tmp_path, format_config, caplog):
+    path = tmp_path / "test.db"
+    kanta = make_kanta(path, Data, format_config)
+    await kanta.open()
+
+    with caplog.at_level(logging.INFO, logger="kanta.transaction"):
+        with kanta.transaction(action="inc", log=False) as data:
+            data.counter = 1
+
+    await kanta.close()
+
+    info_messages = [r for r in caplog.records if r.levelno == logging.INFO]
+    assert not info_messages
+
+
+@pytest.mark.asyncio
+async def test_transaction_log_custom_logger(tmp_path, format_config, caplog):
+    path = tmp_path / "test.db"
+    kanta = make_kanta(path, Data, format_config)
+    await kanta.open()
+
+    custom_logger = logging.getLogger("custom.transaction")
+    custom_logger.setLevel(logging.INFO)
+
+    with caplog.at_level(logging.INFO, logger="custom.transaction"):
+        with kanta.transaction(action="inc", log=custom_logger) as data:
+            data.counter = 1
+
+    await kanta.close()
+
+    info_messages = [r for r in caplog.records if r.levelno == logging.INFO]
+    assert len(info_messages) >= 1
+    assert "inc" in info_messages[0].message
+
+
 @pytest.mark.asyncio
 async def test_open_locked_file_raises_filelock_error(tmp_path, format_config):
     path = tmp_path / "test.db"

tests/test_logging.py

@@ -1,16 +1,47 @@
 import logging
 
-from kanta.logging import configure_logging, log_change
-from kanta.logging import logger
+import pytest
+
+from kanta.logging import configure_logging, log_change, transaction_logger
 
 
-def test_configure_logging():
+@pytest.fixture(autouse=True)
+def _reset_kanta_loggers():
+    yield
+    for name in ("kanta", "kanta.transaction", "kanta.bootstrap", "kanta.migration"):
+        logger = logging.getLogger(name)
+        logger.setLevel(logging.NOTSET)
+        logger.propagate = True
+        logger.handlers.clear()
+
+
+def test_configure_logging_defaults():
+    kanta_logger = logging.getLogger("kanta")
     configure_logging()
-    assert logger.level == logging.INFO
+    assert kanta_logger.level == logging.INFO
+    assert not kanta_logger.propagate
+    assert kanta_logger.handlers
+
+
+def test_configure_logging_disables_specific_loggers():
+    configure_logging(bootstrap=False, migration=False, transaction=False)
+    assert not logging.getLogger("kanta.bootstrap").propagate
+    assert not logging.getLogger("kanta.migration").propagate
+    assert not logging.getLogger("kanta.transaction").propagate
+
+
+def test_configure_logging_skiproot_false_leaves_kanta_propagation():
+    kanta_logger = logging.getLogger("kanta")
+    kanta_logger.handlers.clear()
+    configure_logging(bootstrap=False, skiproot=False)
+    assert kanta_logger.propagate
+    assert not kanta_logger.handlers
+    assert not logging.getLogger("kanta.bootstrap").propagate
 
 
 def test_log_change_no_diff(capsys):
-    logger.handlers.clear()
+    kanta_logger = logging.getLogger("kanta")
+    kanta_logger.handlers.clear()
     configure_logging()
     log_change("test", {})
     captured = capsys.readouterr()

tests/test_migrations.py

@@ -1,4 +1,3 @@
-import logging
 from types import ModuleType, SimpleNamespace
 
 import pytest
@@ -25,8 +24,8 @@ def test_register_and_apply():
         d["version"] = 2
 
     state = {}
-    new_ver = reg.apply(state, current_version=0, kanta=kanta, silent=True)
-    assert new_ver == 2
+    result = reg.apply(state, current_version=0, kanta=kanta)
+    assert result.version == 2
     assert state["version"] == 2
 
 
@@ -39,8 +38,8 @@ def test_no_migrations_needed():
         d["x"] = 1
 
     state = {"x": 1}
-    new_ver = reg.apply(state, current_version=1, kanta=kanta, silent=True)
-    assert new_ver == 1
+    result = reg.apply(state, current_version=1, kanta=kanta)
+    assert result.version == 1
 
 
 def test_from_module():
@@ -60,8 +59,8 @@ def test_from_module():
     assert reg.dbver == 2
 
     state = {}
-    new_ver = reg.apply(state, current_version=0, kanta=kanta, silent=True)
-    assert new_ver == 2
+    result = reg.apply(state, current_version=0, kanta=kanta)
+    assert result.version == 2
     assert state["v"] == 2
 
 
@@ -75,8 +74,8 @@ def test_migrations_can_use_kanta_ctx():
         d["source"] = kanta.ctx.source
 
     state = {}
-    new_ver = reg.apply(state, current_version=0, kanta=kanta, silent=True)
-    assert new_ver == 1
+    result = reg.apply(state, current_version=0, kanta=kanta)
+    assert result.version == 1
     assert state["source"] == "migration"
     assert kanta.ctx.source == "migration"
 
@@ -90,8 +89,8 @@ def test_migration_can_omit_kanta_argument():
         d["x"] = 1
 
     state = {}
-    new_ver = reg.apply(state, current_version=0, kanta=kanta, silent=True)
-    assert new_ver == 1
+    result = reg.apply(state, current_version=0, kanta=kanta)
+    assert result.version == 1
     assert state["x"] == 1
 
 
@@ -107,7 +106,7 @@ def test_version_too_new():
         DatabaseError,
         match="Database version v2 is newer than the highest supported version v1",
     ):
-        reg.apply({}, current_version=2, kanta=kanta, silent=True)
+        reg.apply({}, current_version=2, kanta=kanta)
 
 
 def test_version_too_old():
@@ -122,7 +121,7 @@ def test_version_too_old():
         DatabaseError,
         match="Database version v1 is older than the minimum supported version v2",
     ):
-        reg.apply({}, current_version=1, kanta=kanta, silent=True)
+        reg.apply({}, current_version=1, kanta=kanta)
 
 
 def test_missing_middle_migration_is_skipped():
@@ -138,8 +137,8 @@ def test_missing_middle_migration_is_skipped():
         d["y"] = 3
 
     state = {"x": 1}
-    new_ver = reg.apply(state, current_version=1, kanta=kanta, silent=True)
-    assert new_ver == 3
+    result = reg.apply(state, current_version=1, kanta=kanta)
+    assert result.version == 3
     assert state["x"] == 1
     assert state["y"] == 3
 
@@ -153,12 +152,12 @@ def test_old_migrations_deleted_current_supported():
         d["x"] = 3
 
     state = {"x": 2}
-    new_ver = reg.apply(state, current_version=2, kanta=kanta, silent=True)
-    assert new_ver == 3
+    result = reg.apply(state, current_version=2, kanta=kanta)
+    assert result.version == 3
     assert state["x"] == 3
 
 
-def test_migration_log_only_when_changed(caplog):
+def test_apply_returns_change_information():
     reg = Migrations()
     kanta = _DummyKanta()
 
@@ -177,28 +176,33 @@ def test_migration_log_only_when_changed(caplog):
         """Set y."""
         d["y"] = 3
 
-    with caplog.at_level(logging.INFO, logger="kanta.migrations"):
-        reg.apply({}, current_version=0, kanta=kanta)
+    result = reg.apply({}, current_version=0, kanta=kanta)
+    assert result.version == 3
+    assert len(result.migrations) == 3
 
-    messages = [r.message for r in caplog.records if r.levelno == logging.INFO]
-    assert len(messages) == 2
-    assert "migrate_v1" in messages[0]
-    assert "Set x" in messages[0]
-    assert "migrate_v3" in messages[1]
-    assert "Set y" in messages[1]
+    assert result.migrations[0].name == "migrate_v1"
+    assert result.migrations[0].description == "Set x"
+    assert result.migrations[0].changed is True
+    assert result.migrations[0].diff == {"$replace": {"x": 1}}
+
+    assert result.migrations[1].name == "migrate_v2"
+    assert result.migrations[1].description == "No-op"
+    assert result.migrations[1].changed is False
+    assert result.migrations[1].diff is None
+
+    assert result.migrations[2].name == "migrate_v3"
+    assert result.migrations[2].description == "Set y"
+    assert result.migrations[2].changed is True
+    assert result.migrations[2].diff == {"y": 3}
 
 
-def test_no_op_migration_produces_no_log(caplog):
+def test_description_defaults_to_version_when_no_docstring():
     reg = Migrations()
     kanta = _DummyKanta()
 
     @reg.register
     def migrate_v1(d):
-        """No-op."""
-        pass
+        d["x"] = 1
 
-    with caplog.at_level(logging.INFO, logger="kanta.migrations"):
-        reg.apply({}, current_version=0, kanta=kanta)
-
-    info_messages = [r for r in caplog.records if r.levelno == logging.INFO]
-    assert not info_messages
+    result = reg.apply({}, current_version=0, kanta=kanta)
+    assert result.migrations[0].description == "v1"

tests/test_snapshot.py

@@ -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