import abc
import typing
from .common_utils import IToProto
# Workaround for good IDE and universal for runtime
if typing.TYPE_CHECKING:
from ..v4.protos import ydb_query_pb2
else:
from ..common.protos import ydb_query_pb2
[docs]
class BaseQueryTxMode(IToProto):
"""Abstract class for Query Transaction Modes."""
@property
@abc.abstractmethod
def name(self) -> str:
pass
[docs]
class QuerySnapshotReadOnly(BaseQueryTxMode):
"""All the read operations within a transaction access the database snapshot.
All the data reads are consistent. The snapshot is taken when the transaction begins,
meaning the transaction sees all changes committed before it began.
"""
def __init__(self):
self._name = "snapshot_read_only"
@property
def name(self) -> str:
return self._name
def to_proto(self) -> ydb_query_pb2.SnapshotModeSettings:
return ydb_query_pb2.SnapshotModeSettings()
[docs]
class QuerySerializableReadWrite(BaseQueryTxMode):
"""This mode guarantees that the result of successful parallel transactions is equivalent
to their serial execution, and there are no read anomalies for successful transactions.
"""
def __init__(self):
self._name = "serializable_read_write"
@property
def name(self) -> str:
return self._name
def to_proto(self) -> ydb_query_pb2.SerializableModeSettings:
return ydb_query_pb2.SerializableModeSettings()
[docs]
class QueryOnlineReadOnly(BaseQueryTxMode):
"""Each read operation in the transaction is reading the data that is most recent at execution time.
The consistency of retrieved data depends on the allow_inconsistent_reads setting:
* false (consistent reads): Each individual read operation returns consistent data,
but no consistency is guaranteed between reads.
Reading the same table range twice may return different results.
* true (inconsistent reads): Even the data fetched by a particular
read operation may contain inconsistent results.
"""
def __init__(self, allow_inconsistent_reads: bool = False):
self.allow_inconsistent_reads = allow_inconsistent_reads
self._name = "online_read_only"
@property
def name(self):
return self._name
def to_proto(self) -> ydb_query_pb2.OnlineModeSettings:
return ydb_query_pb2.OnlineModeSettings(allow_inconsistent_reads=self.allow_inconsistent_reads)
[docs]
class QueryStaleReadOnly(BaseQueryTxMode):
"""Read operations within a transaction may return results that are slightly out-of-date
(lagging by fractions of a second). Each individual read returns consistent data,
but no consistency between different reads is guaranteed.
"""
def __init__(self):
self._name = "stale_read_only"
@property
def name(self):
return self._name
def to_proto(self) -> ydb_query_pb2.StaleModeSettings:
return ydb_query_pb2.StaleModeSettings()