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horizontal_shard.py
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# ext/horizontal_shard.py # Copyright (C) 2005-2024 the SQLAlchemy authors and contributors # <see AUTHORS file> # # This module is part of SQLAlchemy and is released under # the MIT License: https://www.opensource.org/licenses/mit-license.php """Horizontal sharding support. Defines a rudimental 'horizontal sharding' system which allows a Session to distribute queries and persistence operations across multiple databases. For a usage example, see the :ref:`examples_sharding` example included in the source distribution. .. deepalchemy:: The horizontal sharding extension is an advanced feature, involving a complex statement -> database interaction as well as use of semi-public APIs for non-trivial cases. Simpler approaches to refering to multiple database "shards", most commonly using a distinct :class:`_orm.Session` per "shard", should always be considered first before using this more complex and less-production-tested system. """ from __future__ import annotations from typing import Any from typing import Callable from typing import Dict from typing import Iterable from typing import Optional from typing import Tuple from typing import Type from typing import TYPE_CHECKING from typing import TypeVar from typing import Union from .. import event from .. import exc from .. import inspect from .. import util from ..orm import PassiveFlag from ..orm._typing import OrmExecuteOptionsParameter from ..orm.interfaces import ORMOption from ..orm.mapper import Mapper from ..orm.query import Query from ..orm.session import _BindArguments from ..orm.session import _PKIdentityArgument from ..orm.session import Session from ..util.typing import Protocol from ..util.typing import Self if TYPE_CHECKING: from ..engine.base import Connection from ..engine.base import Engine from ..engine.base import OptionEngine from ..engine.result import IteratorResult from ..engine.result import Result from ..orm import LoaderCallableStatus from ..orm._typing import _O from ..orm.bulk_persistence import BulkUDCompileState from ..orm.context import QueryContext from ..orm.session import _EntityBindKey from ..orm.session import _SessionBind from ..orm.session import ORMExecuteState from ..orm.state import InstanceState from ..sql import Executable from ..sql._typing import _TP from ..sql.elements import ClauseElement __all__ = ["ShardedSession", "ShardedQuery"] _T = TypeVar("_T", bound=Any) ShardIdentifier = str class ShardChooser(Protocol): def __call__( self, mapper: Optional[Mapper[_T]], instance: Any, clause: Optional[ClauseElement], ) -> Any: ... class IdentityChooser(Protocol): def __call__( self, mapper: Mapper[_T], primary_key: _PKIdentityArgument, *, lazy_loaded_from: Optional[InstanceState[Any]], execution_options: OrmExecuteOptionsParameter, bind_arguments: _BindArguments, **kw: Any, ) -> Any: ... class ShardedQuery(Query[_T]): """Query class used with :class:`.ShardedSession`. .. legacy:: The :class:`.ShardedQuery` is a subclass of the legacy :class:`.Query` class. The :class:`.ShardedSession` now supports 2.0 style execution via the :meth:`.ShardedSession.execute` method. """ def __init__(self, *args: Any, **kwargs: Any) -> None: super().__init__(*args, **kwargs) assert isinstance(self.session, ShardedSession) self.identity_chooser = self.session.identity_chooser self.execute_chooser = self.session.execute_chooser self._shard_id = None def set_shard(self, shard_id: ShardIdentifier) -> Self: """Return a new query, limited to a single shard ID. All subsequent operations with the returned query will be against the single shard regardless of other state. The shard_id can be passed for a 2.0 style execution to the bind_arguments dictionary of :meth:`.Session.execute`:: results = session.execute( stmt, bind_arguments={"shard_id": "my_shard"} ) """ return self.execution_options(_sa_shard_id=shard_id) class ShardedSession(Session): shard_chooser: ShardChooser identity_chooser: IdentityChooser execute_chooser: Callable[[ORMExecuteState], Iterable[Any]] def __init__( self, shard_chooser: ShardChooser, identity_chooser: Optional[IdentityChooser] = None, execute_chooser: Optional[ Callable[[ORMExecuteState], Iterable[Any]] ] = None, shards: Optional[Dict[str, Any]] = None, query_cls: Type[Query[_T]] = ShardedQuery, *, id_chooser: Optional[ Callable[[Query[_T], Iterable[_T]], Iterable[Any]] ] = None, query_chooser: Optional[Callable[[Executable], Iterable[Any]]] = None, **kwargs: Any, ) -> None: """Construct a ShardedSession. :param shard_chooser: A callable which, passed a Mapper, a mapped instance, and possibly a SQL clause, returns a shard ID. This id may be based off of the attributes present within the object, or on some round-robin scheme. If the scheme is based on a selection, it should set whatever state on the instance to mark it in the future as participating in that shard. :param identity_chooser: A callable, passed a Mapper and primary key argument, which should return a list of shard ids where this primary key might reside. .. versionchanged:: 2.0 The ``identity_chooser`` parameter supersedes the ``id_chooser`` parameter. :param execute_chooser: For a given :class:`.ORMExecuteState`, returns the list of shard_ids where the query should be issued. Results from all shards returned will be combined together into a single listing. .. versionchanged:: 1.4 The ``execute_chooser`` parameter supersedes the ``query_chooser`` parameter. :param shards: A dictionary of string shard names to :class:`~sqlalchemy.engine.Engine` objects. """ super().__init__(query_cls=query_cls, **kwargs) event.listen( self, "do_orm_execute", execute_and_instances, retval=True ) self.shard_chooser = shard_chooser if id_chooser: _id_chooser = id_chooser util.warn_deprecated( "The ``id_chooser`` parameter is deprecated; " "please use ``identity_chooser``.", "2.0", ) def _legacy_identity_chooser( mapper: Mapper[_T], primary_key: _PKIdentityArgument, *, lazy_loaded_from: Optional[InstanceState[Any]], execution_options: OrmExecuteOptionsParameter, bind_arguments: _BindArguments, **kw: Any, ) -> Any: q = self.query(mapper) if lazy_loaded_from: q = q._set_lazyload_from(lazy_loaded_from) return _id_chooser(q, primary_key) self.identity_chooser = _legacy_identity_chooser elif identity_chooser: self.identity_chooser = identity_chooser else: raise exc.ArgumentError( "identity_chooser or id_chooser is required" ) if query_chooser: _query_chooser = query_chooser util.warn_deprecated( "The ``query_chooser`` parameter is deprecated; " "please use ``execute_chooser``.", "1.4", ) if execute_chooser: raise exc.ArgumentError( "Can't pass query_chooser and execute_chooser " "at the same time." ) def _default_execute_chooser( orm_context: ORMExecuteState, ) -> Iterable[Any]: return _query_chooser(orm_context.statement) if execute_chooser is None: execute_chooser = _default_execute_chooser if execute_chooser is None: raise exc.ArgumentError( "execute_chooser or query_chooser is required" ) self.execute_chooser = execute_chooser self.__shards: Dict[ShardIdentifier, _SessionBind] = {} if shards is not None: for k in shards: self.bind_shard(k, shards[k]) def _identity_lookup( self, mapper: Mapper[_O], primary_key_identity: Union[Any, Tuple[Any, ...]], identity_token: Optional[Any] = None, passive: PassiveFlag = PassiveFlag.PASSIVE_OFF, lazy_loaded_from: Optional[InstanceState[Any]] = None, execution_options: OrmExecuteOptionsParameter = util.EMPTY_DICT, bind_arguments: Optional[_BindArguments] = None, **kw: Any, ) -> Union[Optional[_O], LoaderCallableStatus]: """override the default :meth:`.Session._identity_lookup` method so that we search for a given non-token primary key identity across all possible identity tokens (e.g. shard ids). .. versionchanged:: 1.4 Moved :meth:`.Session._identity_lookup` from the :class:`_query.Query` object to the :class:`.Session`. """ if identity_token is not None: obj = super()._identity_lookup( mapper, primary_key_identity, identity_token=identity_token, **kw, ) return obj else: for shard_id in self.identity_chooser( mapper, primary_key_identity, lazy_loaded_from=lazy_loaded_from, execution_options=execution_options, bind_arguments=dict(bind_arguments) if bind_arguments else {}, ): obj2 = super()._identity_lookup( mapper, primary_key_identity, identity_token=shard_id, lazy_loaded_from=lazy_loaded_from, **kw, ) if obj2 is not None: return obj2 return None def _choose_shard_and_assign( self, mapper: Optional[_EntityBindKey[_O]], instance: Any, **kw: Any, ) -> Any: if instance is not None: state = inspect(instance) if state.key: token = state.key[2] assert token is not None return token elif state.identity_token: return state.identity_token assert isinstance(mapper, Mapper) shard_id = self.shard_chooser(mapper, instance, **kw) if instance is not None: state.identity_token = shard_id return shard_id def connection_callable( # type: ignore [override] self, mapper: Optional[Mapper[_T]] = None, instance: Optional[Any] = None, shard_id: Optional[ShardIdentifier] = None, **kw: Any, ) -> Connection: """Provide a :class:`_engine.Connection` to use in the unit of work flush process. """ if shard_id is None: shard_id = self._choose_shard_and_assign(mapper, instance) if self.in_transaction(): trans = self.get_transaction() assert trans is not None return trans.connection(mapper, shard_id=shard_id) else: bind = self.get_bind( mapper=mapper, shard_id=shard_id, instance=instance ) if isinstance(bind, Engine): return bind.connect(**kw) else: assert isinstance(bind, Connection) return bind def get_bind( self, mapper: Optional[_EntityBindKey[_O]] = None, *, shard_id: Optional[ShardIdentifier] = None, instance: Optional[Any] = None, clause: Optional[ClauseElement] = None, **kw: Any, ) -> _SessionBind: if shard_id is None: shard_id = self._choose_shard_and_assign( mapper, instance=instance, clause=clause ) assert shard_id is not None return self.__shards[shard_id] def bind_shard( self, shard_id: ShardIdentifier, bind: Union[Engine, OptionEngine] ) -> None: self.__shards[shard_id] = bind class set_shard_id(ORMOption): """a loader option for statements to apply a specific shard id to the primary query as well as for additional relationship and column loaders. The :class:`_horizontal.set_shard_id` option may be applied using the :meth:`_sql.Executable.options` method of any executable statement:: stmt = ( select(MyObject). where(MyObject.name == 'some name'). options(set_shard_id("shard1")) ) Above, the statement when invoked will limit to the "shard1" shard identifier for the primary query as well as for all relationship and column loading strategies, including eager loaders such as :func:`_orm.selectinload`, deferred column loaders like :func:`_orm.defer`, and the lazy relationship loader :func:`_orm.lazyload`. In this way, the :class:`_horizontal.set_shard_id` option has much wider scope than using the "shard_id" argument within the :paramref:`_orm.Session.execute.bind_arguments` dictionary. .. versionadded:: 2.0.0 """ __slots__ = ("shard_id", "propagate_to_loaders") def __init__( self, shard_id: ShardIdentifier, propagate_to_loaders: bool = True ): """Construct a :class:`_horizontal.set_shard_id` option. :param shard_id: shard identifier :param propagate_to_loaders: if left at its default of ``True``, the shard option will take place for lazy loaders such as :func:`_orm.lazyload` and :func:`_orm.defer`; if False, the option will not be propagated to loaded objects. Note that :func:`_orm.defer` always limits to the shard_id of the parent row in any case, so the parameter only has a net effect on the behavior of the :func:`_orm.lazyload` strategy. """ self.shard_id = shard_id self.propagate_to_loaders = propagate_to_loaders def execute_and_instances( orm_context: ORMExecuteState, ) -> Union[Result[_T], IteratorResult[_TP]]: active_options: Union[ None, QueryContext.default_load_options, Type[QueryContext.default_load_options], BulkUDCompileState.default_update_options, Type[BulkUDCompileState.default_update_options], ] if orm_context.is_select: active_options = orm_context.load_options elif orm_context.is_update or orm_context.is_delete: active_options = orm_context.update_delete_options else: active_options = None session = orm_context.session assert isinstance(session, ShardedSession) def iter_for_shard( shard_id: ShardIdentifier, ) -> Union[Result[_T], IteratorResult[_TP]]: bind_arguments = dict(orm_context.bind_arguments) bind_arguments["shard_id"] = shard_id orm_context.update_execution_options(identity_token=shard_id) return orm_context.invoke_statement(bind_arguments=bind_arguments) for orm_opt in orm_context._non_compile_orm_options: # TODO: if we had an ORMOption that gets applied at ORM statement # execution time, that would allow this to be more generalized. # for now just iterate and look for our options if isinstance(orm_opt, set_shard_id): shard_id = orm_opt.shard_id break else: if active_options and active_options._identity_token is not None: shard_id = active_options._identity_token elif "_sa_shard_id" in orm_context.execution_options: shard_id = orm_context.execution_options["_sa_shard_id"] elif "shard_id" in orm_context.bind_arguments: shard_id = orm_context.bind_arguments["shard_id"] else: shard_id = None if shard_id is not None: return iter_for_shard(shard_id) else: partial = [] for shard_id in session.execute_chooser(orm_context): result_ = iter_for_shard(shard_id) partial.append(result_) return partial[0].merge(*partial[1:])