ashb commented on code in PR #73920: URL: https://github.com/apache/airflow/pull/73920#discussion_r4154036066
########## airflow-core/src/airflow/migrations/versions/0142_3_4_0_remove_duplicate_dag_run_state_dag_id_indexes.py: ########## @@ -0,0 +1,120 @@ +# +# 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. + +""" +Remove duplicate ``(state, dag_id)`` indexes on ``dag_run``. + +MySQL has no partial indexes, so ``idx_dag_run_queued_dags`` and ``idx_dag_run_running_dags`` +are both plain indexes on ``(state, dag_id)`` there. ``idx_dag_run_queued_dags`` is dropped; +``idx_dag_run_running_dags`` is kept because the scheduler names it in a MySQL ``USE INDEX`` hint. + +On Postgres the squashed 2.6.2 migration created both without their ``WHERE`` predicate, so +databases built from migration files (``--use-migration-files``) have the same duplicate. +Those are recreated as the partial indexes the ORM declares; databases that already have the +partial indexes are left untouched. + +Revision ID: 9f8d3473abf9 +Revises: e5a91c7f42b3 +Create Date: 2026-09-28 12:10:05.000000 + +""" + +from __future__ import annotations + +import sqlalchemy as sa +from alembic import context, op + +revision = "9f8d3473abf9" +down_revision = "e5a91c7f42b3" +branch_labels = None +depends_on = None +airflow_version = "3.4.0" + +_TABLE = "dag_run" +_INDEX = "idx_dag_run_queued_dags" +_EXISTS_QUERY = ( + "SELECT COUNT(*) FROM information_schema.STATISTICS " + f"WHERE TABLE_SCHEMA = DATABASE() AND TABLE_NAME = '{_TABLE}' AND INDEX_NAME = '{_INDEX}'" +) +_POSTGRES_PARTIAL_INDEXES = { + "idx_dag_run_queued_dags": "queued", + "idx_dag_run_running_dags": "running", +} + + +def _make_postgres_index_partial(conn, index: str, state: str) -> None: + """ + Recreate ``index`` with its ``WHERE state = <state>`` predicate if it currently has none. + + A ``DO`` block keeps the check server-side, so the same SQL works in offline (``--sql``) mode. + """ + conn.execute( + sa.text(f""" + DO $$ + BEGIN + IF EXISTS ( + SELECT 1 FROM pg_index WHERE indexrelid = to_regclass('{index}') AND indpred IS NULL + ) THEN + DROP INDEX {index}; + CREATE INDEX {index} ON {_TABLE} (state, dag_id) WHERE state = '{state}'; + END IF; + END $$; + """) + ) + + +def _run_if_index_exists(conn, *, exists: bool, statement: str) -> None: + """ + Run ``statement`` only when the index's presence matches ``exists``. + + MySQL has no ``DROP INDEX IF EXISTS`` / ``CREATE INDEX IF NOT EXISTS``, and a user may + already have dropped the duplicate by hand. In offline (``--sql``) mode there is no live + connection to check against, so the guard is emitted as a prepared statement instead. + """ + if context.is_offline_mode(): + conn.execute( + sa.text(f""" + set @var=if(({_EXISTS_QUERY}) {"> 0" if exists else "= 0"},'{statement}','select 1'); + + prepare stmt from @var; + execute stmt; + deallocate prepare stmt; + """) + ) + return + if bool(conn.execute(sa.text(_EXISTS_QUERY)).scalar()) is exists: + conn.execute(sa.text(statement)) + + +def upgrade(): + """Remove duplicate ``(state, dag_id)`` indexes on ``dag_run``.""" + conn = op.get_bind() + if conn.dialect.name == "mysql": + _run_if_index_exists(conn, exists=True, statement=f"DROP INDEX {_INDEX} ON {_TABLE}") + elif conn.dialect.name == "postgresql": + for index, state in _POSTGRES_PARTIAL_INDEXES.items(): + _make_postgres_index_partial(conn, index, state) Review Comment: Ohhhh I see. I wasn't even aware of the `--use-migration-files` option. -- 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]
