jroachgolf84 commented on code in PR #67299: URL: https://github.com/apache/airflow/pull/67299#discussion_r3313141780
########## airflow-core/docs/administration-and-deployment/state-store.rst: ########## @@ -0,0 +1,247 @@ + .. Licensed to the Apache Software Foundation (ASF) under one + or more contributor license agreements. See the NOTICE file + distributed with this work for additional information + regarding copyright ownership. The ASF licenses this file + to you under the Apache License, Version 2.0 (the + "License"); you may not use this file except in compliance + with the License. You may obtain a copy of the License at + + .. http://www.apache.org/licenses/LICENSE-2.0 + + .. Unless required by applicable law or agreed to in writing, + software distributed under the License is distributed on an + "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY + KIND, either express or implied. See the License for the + specific language governing permissions and limitations + under the License. + +.. _state-store: + +State Store Configuration +========================== + +.. versionadded:: 3.3 + +The state store is the persistence layer for :doc:`task state </core-concepts/task-state>` and :doc:`asset state </authoring-and-scheduling/asset-state>`. By default, both are stored in the Airflow metadata database. This page describes the available configuration options, garbage-collection semantics, and how to provide a custom backend. + +Configuration reference +----------------------- + +All options live under the ``[state_store]`` section of ``airflow.cfg``. + +.. note:: + + The config section is ``[state_store]``, **not** ``[task_state]``. + +``backend`` +~~~~~~~~~~~ + +Full dotted path to a class that implements :class:`~airflow.sdk.state.BaseStateBackend`. Defaults to the built-in metastore backend. + +.. code-block:: ini + + [state_store] + backend = mypackage.state.CustomStateBackend + +``default_retention_days`` +~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Number of days to retain **task state** rows after their last update. Rows older than this are deleted during the next GC pass. + +* Set to ``0`` to disable time-based cleanup entirely. +* Default: ``30``. +* This setting does **not** apply to asset state rows. + +.. code-block:: ini + + [state_store] + default_retention_days = 30 + +``clear_on_success`` +~~~~~~~~~~~~~~~~~~~~ + +When ``True``, all task state keys for a task instance are automatically deleted when that task instance moves to the ``success`` state. Defaults to ``False``, which preserves task state after success for observability (e.g.the submitted job ID or the last row count is still readable from the UI orREST API after the run completes). + +.. important:: + + ``clear_on_success`` clears **task state only**. It has no effect on asset state. Asset state is scoped to the asset rather than the task instance and must be cleared explicitly. + +.. code-block:: ini + + [state_store] + clear_on_success = False + +``state_cleanup_batch_size`` +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Number of rows deleted per batch during GC cleanup. Set to ``0`` (default) to delete all matching rows in a single statement. Tune this on deployments with large ``task_state`` tables to reduce lock contention. + +.. code-block:: ini + + [state_store] + state_cleanup_batch_size = 10000 + +Worker-side backend (``[workers] state_backend``) +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +A separate, optional config key under ``[workers]`` lets you route task state and asset state values through a worker-side backend before they reach the API server. + +.. code-block:: ini + + [workers] + state_backend = mypackage.state.S3StateBackend + +When this is set, ``TaskStateAccessor.set()`` calls ``serialize_task_state_to_ref()`` on the worker-side backend before sending the value to the Execution API, and ``get()`` calls ``deserialize_task_state_from_ref()`` after receiving the stored reference. See `Custom worker-side backends`_ below. + + +Garbage collection semantics +----------------------------- + +The GC job runs periodically and removes state rows according to the following rules: + +**Time-based expiry (task state only)** + Rows whose ``expires_at < now()`` are deleted. ``expires_at`` is computed on the *worker* at write time, not by the server. + +**``default_retention_days`` fallback (task state only)** + Keys written with no explicit ``retention`` (i.e. ``expires_at`` is ``NULL``) are governed by the global ``default_retention_days`` setting. When this setting is positive, the GC job treats such rows as expiring ``default_retention_days`` days after their last update. + +**``NEVER_EXPIRE`` keys** + Keys set with ``retention=NEVER_EXPIRE`` are stored with ``expires_at = NULL`` and a flag that tells the GC to skip them unconditionally. They are never deleted by time-based cleanup, regardless of ``default_retention_days``. + +**Orphan sweep (asset state)** + Asset state rows for assets that no longer have an ``asset_active`` record are deleted during the orphan-sweep pass. This cleans up state for deactivated or renamed assets. + + +Custom backends +--------------- + +To replace the default metastore backend, subclass :class:`~airflow.sdk.state.BaseStateBackend` and implement all eight abstract methods. + +Abstract methods +~~~~~~~~~~~~~~~~ + +There are four synchronous methods and four async equivalents: + +.. list-table:: + :header-rows: 1 + :widths: 30 70 + + * - Method + - Description + * - ``get(scope, key, *, session)`` + - Return the stored value, or ``None``. + * - ``set(scope, key, value, *, expires_at, session)`` + - Write or overwrite a key. ``expires_at`` is a UTC datetime or ``None`` + for non-expiring keys. + * - ``delete(scope, key, *, session)`` + - Delete a single key; no-op if absent. + * - ``clear(scope, *, all_map_indices, session)`` + - Delete all keys under the scope. + * - ``aget(scope, key, *, session)`` + - Async variant of ``get``. + * - ``aset(scope, key, value, *, expires_at, session)`` + - Async variant of ``set``. + * - ``adelete(scope, key, *, session)`` + - Async variant of ``delete``. + * - ``aclear(scope, *, all_map_indices, session)`` + - Async variant of ``clear``. + +Dispatching on scope type +~~~~~~~~~~~~~~~~~~~~~~~~~ + +Each method receives a ``scope`` argument that is either a :class:`~airflow.sdk.state.TaskScope` or an :class:`~airflow.sdk.state.AssetScope`. Use a ``match`` statement to dispatch: + +.. code-block:: python + + from airflow.sdk.state import BaseStateBackend, TaskScope, AssetScope + + + class MyBackend(BaseStateBackend): + def get(self, scope, key, *, session=None): + if scope == TaskScope(): + return self._task_store.get(scope, key) + elif scope == AssetScope(): + return self._asset_store.get(scope, key) + +:class:`~airflow.sdk.state.AssetScope` has three optional fields: ``asset_id`` (integer, server-side only), ``name``, and ``uri``. At least one must be set. Server-side operations (REST API calls) provide ``asset_id``. Worker-side operations provide ``name`` or ``uri`` (workers do not have access to the integer ``asset_id``). + +Configure the class via ``[state_store] backend``: + +.. code-block:: ini + + [state_store] + backend = mypackage.state.MyBackend + + +Custom worker-side backends +---------------------------- + +Worker-side backends extend ``BaseStateBackend`` with two pairs of serialization hooks. They are configured separately via ``[workers] state_backend`` and run *on the worker process*, not on the API server. This lets you store large payloads or credentialed data directly on worker infrastructure while only a compact reference string is kept in the database. + +Override these four methods: + +``serialize_task_state_to_ref(*, value, key, ti_id)`` +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Called by ``TaskStateAccessor.set()`` before sending the value to the Execution API. Return a reference string (e.g. an S3 key) that will be stored in the database instead of the raw value. + +``deserialize_task_state_from_ref(stored)`` +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Called by ``TaskStateAccessor.get()`` after retrieving the reference string from the Execution API. Return the actual value. + +``serialize_asset_state_to_ref(*, value, key, asset_ref)`` +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Same as the task variant, but for asset state. ``asset_ref`` is the asset name or URI, depending on how the accessor was constructed. + +``deserialize_asset_state_from_ref(stored)`` +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Called by ``AssetStateAccessor.get()`` to resolve the stored reference back to the actual value. + +.. important:: + + **References must be deterministic.** Given the same inputs (``ti_id`` + ``key`` for task state; ``asset_ref`` + ``key`` for asset state), the serialization method must always return the same reference string. Do not embed timestamps, random UUIDs, or any other non-deterministic component in the reference path. + + When a key is deleted or cleared, Airflow clears the database reference *first*, then calls the backend's ``delete()`` or ``clear()`` method. If backend cleanup fails after the DB row is gone, the external object is orphaned. Because the reference is deterministic, a subsequent ``set()`` for the same key will overwrite the orphaned object, making the failure recoverable. A non-deterministic reference would leave the external object permanently orphaned with no way to locate it. + +Example skeleton: + +.. code-block:: python + + from airflow.sdk.state import BaseStateBackend, TaskScope, AssetScope + + + class S3StateBackend(BaseStateBackend): Review Comment: Added. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
