Remove usused index on task instance (apache#36737)

Index is only helpful for a user's custom query -- not for airflow in general (see comment apache#30762 (comment)).  Noticed that this query had zero scans over a period of months.  I also observed that it also takes up as much space as the table itself.  Since it's not generally useful, it doesn't belong in airflow OSS.

Reverts apache#30762

airflow/migrations/versions/0126_2_7_0_add_index_to_task_instance_table.py

@@ -37,14 +37,16 @@
 
 def upgrade():
     """Apply Add index to task_instance table"""
-    op.create_index(
-        "ti_state_incl_start_date",
-        "task_instance",
-        ["dag_id", "task_id", "state"],
-        postgresql_include=["start_date"],
-    )
+    # We don't add this index anymore because it's not useful.
+    pass
 
 
 def downgrade():
     """Unapply Add index to task_instance table"""
-    op.drop_index("ti_state_incl_start_date", table_name="task_instance")
+    # At 2.8.1 we removed this index as it is not used, and changed this migration not to add it
+    # So we use drop if exists (cus it might not be there)
+    import sqlalchemy
+    from contextlib import suppress
+
+    with suppress(sqlalchemy.exc.DatabaseError):  # mysql does not support drop if exists index
+        op.drop_index("ti_state_incl_start_date", table_name="task_instance", if_exists=True)

airflow/migrations/versions/0133_2_8_1_refactor_dag_run_indexes.py

@@ -0,0 +1,50 @@
+#
+# 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.
+
+"""Drop unused TI index
+
+Revision ID: 88344c1d9134
+Revises: 10b52ebd31f7
+Create Date: 2024-01-11 11:54:48.232030
+
+"""
+
+import sqlalchemy as sa
+from alembic import op
+
+
+# revision identifiers, used by Alembic.
+revision = "88344c1d9134"
+down_revision = "10b52ebd31f7"
+branch_labels = None
+depends_on = None
+airflow_version = "2.8.1"
+
+
+def upgrade():
+    """Apply refactor dag run indexes"""
+    # This index may have been created in 2.7 but we've since removed it from migrations
+    import sqlalchemy
+    from contextlib import suppress
+
+    with suppress(sqlalchemy.exc.DatabaseError):  # mysql does not support drop if exists index
+        op.drop_index("ti_state_incl_start_date", table_name="task_instance", if_exists=True)
+
+
+def downgrade():
+    """Unapply refactor dag run indexes"""

airflow/models/taskinstance.py

@@ -1259,7 +1259,6 @@ class TaskInstance(Base, LoggingMixin):
         # Existing "ti_state_lkp" is not enough for such query when this table has millions of rows, since
         # rows have to be fetched in order to retrieve the start_date column. With this index, INDEX ONLY SCAN
         # is performed and that query runs within milliseconds.
-        Index("ti_state_incl_start_date", dag_id, task_id, state, postgresql_include=["start_date"]),
         Index("ti_pool", pool, state, priority_weight),
         Index("ti_job_id", job_id),
         Index("ti_trigger_id", trigger_id),

airflow/utils/db.py

@@ -89,6 +89,7 @@
     "2.6.2": "c804e5c76e3e",
     "2.7.0": "405de8318b3a",
     "2.8.0": "10b52ebd31f7",
+    "2.8.1": "88344c1d9134",
 }
 
 

docs/apache-airflow/img/airflow_erd.sha256

@@ -1 +1 @@
-194706fc390025f473f73ce934bfe4b394b50ce76748e5df33ae643e38538357
+243075d59223245db8034a97c7d6f53bd8a39ee0dc02831229a6ec743c2c920a

docs/apache-airflow/migrations-ref.rst

@@ -39,7 +39,9 @@ Here's the list of all the Database Migrations that are executed via when you ru
 +---------------------------------+-------------------+-------------------+--------------------------------------------------------------+
 | Revision ID                     | Revises ID        | Airflow Version   | Description                                                  |
 +=================================+===================+===================+==============================================================+
-| ``10b52ebd31f7`` (head)         | ``bd5dfbe21f88``  | ``2.8.0``         | Add processor_subdir to ImportError.                         |
+| ``88344c1d9134`` (head)         | ``10b52ebd31f7``  | ``2.8.1``         | Drop unused TI index                                         |
++---------------------------------+-------------------+-------------------+--------------------------------------------------------------+
+| ``10b52ebd31f7``                | ``bd5dfbe21f88``  | ``2.8.0``         | Add processor_subdir to ImportError.                         |
 +---------------------------------+-------------------+-------------------+--------------------------------------------------------------+
 | ``bd5dfbe21f88``                | ``f7bf2a57d0a6``  | ``2.8.0``         | Make connection login/password TEXT                          |
 +---------------------------------+-------------------+-------------------+--------------------------------------------------------------+