Remove the old ix_states_event_id index if its no longer being used (#89901)

* Remove the old ix_states_event_id index if its no longer being used

* cover it

* fixes

* fixup

* Update homeassistant/components/recorder/tasks.py

homeassistant/components/recorder/const.py

@@ -48,6 +48,8 @@ CONTEXT_ID_AS_BINARY_SCHEMA_VERSION = 36
 EVENT_TYPE_IDS_SCHEMA_VERSION = 37
 STATES_META_SCHEMA_VERSION = 38
 
+LEGACY_STATES_EVENT_ID_INDEX_SCHEMA_VERSION = 28
+
 
 class SupportedDialect(StrEnum):
     """Supported dialects."""

homeassistant/components/recorder/core.py

@@ -46,6 +46,7 @@ from .const import (
     DOMAIN,
     EVENT_TYPE_IDS_SCHEMA_VERSION,
     KEEPALIVE_TIME,
+    LEGACY_STATES_EVENT_ID_INDEX_SCHEMA_VERSION,
     MARIADB_PYMYSQL_URL_PREFIX,
     MARIADB_URL_PREFIX,
     MAX_QUEUE_BACKLOG,
@@ -57,7 +58,9 @@ from .const import (
     SupportedDialect,
 )
 from .db_schema import (
+    LEGACY_STATES_EVENT_ID_INDEX,
     SCHEMA_VERSION,
+    TABLE_STATES,
     Base,
     EventData,
     Events,
@@ -93,6 +96,7 @@ from .tasks import (
     CompileMissingStatisticsTask,
     DatabaseLockTask,
     EntityIDMigrationTask,
+    EventIdMigrationTask,
     EventsContextIDMigrationTask,
     EventTask,
     EventTypeIDMigrationTask,
@@ -113,6 +117,7 @@ from .util import (
     dburl_to_path,
     end_incomplete_runs,
     execute_stmt_lambda_element,
+    get_index_by_name,
     is_second_sunday,
     move_away_broken_database,
     session_scope,
@@ -730,6 +735,15 @@ class Recorder(threading.Thread):
                 _LOGGER.debug("Activating states_meta manager as all data is migrated")
                 self.states_meta_manager.active = True
 
+            if self.schema_version > LEGACY_STATES_EVENT_ID_INDEX_SCHEMA_VERSION:
+                with contextlib.suppress(SQLAlchemyError):
+                    # If the index of event_ids on the states table is still present
+                    # we need to queue a task to remove it.
+                    if get_index_by_name(
+                        session, TABLE_STATES, LEGACY_STATES_EVENT_ID_INDEX
+                    ):
+                        self.queue_task(EventIdMigrationTask())
+
         # We must only set the db ready after we have set the table managers
         # to active if there is no data to migrate.
         #
@@ -1138,6 +1152,10 @@ class Recorder(threading.Thread):
         """Post migrate entity_ids if needed."""
         return migration.post_migrate_entity_ids(self)
 
+    def _cleanup_legacy_states_event_ids(self) -> bool:
+        """Cleanup legacy event_ids if needed."""
+        return migration.cleanup_legacy_states_event_ids(self)
+
     def _send_keep_alive(self) -> None:
         """Send a keep alive to keep the db connection open."""
         assert self.event_session is not None

homeassistant/components/recorder/db_schema.py

@@ -116,6 +116,7 @@ LAST_UPDATED_INDEX_TS = "ix_states_last_updated_ts"
 METADATA_ID_LAST_UPDATED_INDEX_TS = "ix_states_metadata_id_last_updated_ts"
 EVENTS_CONTEXT_ID_BIN_INDEX = "ix_events_context_id_bin"
 STATES_CONTEXT_ID_BIN_INDEX = "ix_states_context_id_bin"
+LEGACY_STATES_EVENT_ID_INDEX = "ix_states_event_id"
 CONTEXT_ID_BIN_MAX_LENGTH = 16
 
 _DEFAULT_TABLE_ARGS = {
@@ -385,9 +386,7 @@ class States(Base):
     attributes: Mapped[str | None] = mapped_column(
         Text().with_variant(mysql.LONGTEXT, "mysql", "mariadb")
     )  # no longer used for new rows
-    event_id: Mapped[int | None] = mapped_column(  # no longer used for new rows
-        Integer, ForeignKey("events.event_id", ondelete="CASCADE"), index=True
-    )
+    event_id: Mapped[int | None] = mapped_column(Integer)  # no longer used for new rows
     last_changed: Mapped[datetime | None] = mapped_column(
         DATETIME_TYPE
     )  # no longer used for new rows

homeassistant/components/recorder/migration.py

@@ -30,6 +30,7 @@ from homeassistant.util.ulid import ulid_to_bytes
 from .const import SupportedDialect
 from .db_schema import (
     CONTEXT_ID_BIN_MAX_LENGTH,
+    LEGACY_STATES_EVENT_ID_INDEX,
     SCHEMA_VERSION,
     STATISTICS_TABLES,
     TABLE_STATES,
@@ -51,6 +52,7 @@ from .queries import (
     find_event_type_to_migrate,
     find_events_context_ids_to_migrate,
     find_states_context_ids_to_migrate,
+    has_used_states_event_ids,
 )
 from .statistics import (
     correct_db_schema as statistics_correct_db_schema,
@@ -64,7 +66,12 @@ from .tasks import (
     PostSchemaMigrationTask,
     StatisticsTimestampMigrationCleanupTask,
 )
-from .util import database_job_retry_wrapper, retryable_database_job, session_scope
+from .util import (
+    database_job_retry_wrapper,
+    get_index_by_name,
+    retryable_database_job,
+    session_scope,
+)
 
 if TYPE_CHECKING:
     from . import Recorder
@@ -308,18 +315,7 @@ def _drop_index(
         with session_scope(session=session_maker()) as session, contextlib.suppress(
             SQLAlchemyError
         ):
-            connection = session.connection()
-            inspector = sqlalchemy.inspect(connection)
-            indexes = inspector.get_indexes(table_name)
-            if index_to_drop := next(
-                (
-                    possible_index["name"]
-                    for possible_index in indexes
-                    if possible_index["name"]
-                    and possible_index["name"].endswith(f"_{index_name}")
-                ),
-                None,
-            ):
+            if index_to_drop := get_index_by_name(session, table_name, index_name):
                 connection.execute(text(f"DROP INDEX {index_to_drop}"))
                 success = True
 
@@ -593,7 +589,7 @@ def _apply_update(  # noqa: C901
         # but it was removed in version 32
     elif new_version == 5:
         # Create supporting index for States.event_id foreign key
-        _create_index(session_maker, "states", "ix_states_event_id")
+        _create_index(session_maker, "states", LEGACY_STATES_EVENT_ID_INDEX)
     elif new_version == 6:
         _add_columns(
             session_maker,
@@ -1529,6 +1525,33 @@ def post_migrate_entity_ids(instance: Recorder) -> bool:
     return is_done
 
 
+@retryable_database_job("cleanup_legacy_event_ids")
+def cleanup_legacy_states_event_ids(instance: Recorder) -> bool:
+    """Remove old event_id index from states.
+
+    We used to link states to events using the event_id column but we no
+    longer store state changed events in the events table.
+
+    If all old states have been purged and existing states are in the new
+    format we can drop the index since it can take up ~10MB per 1M rows.
+    """
+    session_maker = instance.get_session
+    _LOGGER.debug("Cleanup legacy entity_ids")
+    with session_scope(session=session_maker()) as session:
+        result = session.execute(has_used_states_event_ids()).scalar()
+        # In the future we may migrate existing states to the new format
+        # but in practice very few of these still exist in production and
+        # removing the index is the likely all that needs to happen.
+        all_gone = not result
+
+    if all_gone:
+        # Only drop the index if there are no more event_ids in the states table
+        # ex all NULL
+        _drop_index(session_maker, "states", LEGACY_STATES_EVENT_ID_INDEX)
+
+    return True
+
+
 def _initialize_database(session: Session) -> bool:
     """Initialize a new database.
 

homeassistant/components/recorder/queries.py

@@ -745,6 +745,13 @@ def batch_cleanup_entity_ids() -> StatementLambdaElement:
     )
 
 
+def has_used_states_event_ids() -> StatementLambdaElement:
+    """Check if there are used event_ids in the states table."""
+    return lambda_stmt(
+        lambda: select(States.state_id).filter(States.event_id.isnot(None)).limit(1)
+    )
+
+
 def has_events_context_ids_to_migrate() -> StatementLambdaElement:
     """Check if there are events context ids to migrate."""
     return lambda_stmt(

homeassistant/components/recorder/tasks.py

@@ -438,3 +438,17 @@ class EntityIDPostMigrationTask(RecorderTask):
         ):
             # Schedule a new migration task if this one didn't finish
             instance.queue_task(EntityIDPostMigrationTask())
+
+
+@dataclass
+class EventIdMigrationTask(RecorderTask):
+    """An object to insert into the recorder queue to cleanup legacy event_ids in the states table.
+
+    This task should only be queued if the ix_states_event_id index exists
+    since it is used to scan the states table and it will be removed after this
+    task is run if its no longer needed.
+    """
+
+    def run(self, instance: Recorder) -> None:
+        """Clean up the legacy event_id index on states."""
+        instance._cleanup_legacy_states_event_ids()  # pylint: disable=[protected-access]

homeassistant/components/recorder/util.py

@@ -18,7 +18,7 @@ from awesomeversion import (
     AwesomeVersionStrategy,
 )
 import ciso8601
-from sqlalchemy import text
+from sqlalchemy import inspect, text
 from sqlalchemy.engine import Result, Row
 from sqlalchemy.exc import OperationalError, SQLAlchemyError
 from sqlalchemy.orm.query import Query
@@ -832,3 +832,22 @@ def chunked(iterable: Iterable, chunked_num: int) -> Iterable[Any]:
     From more-itertools
     """
     return iter(partial(take, chunked_num, iter(iterable)), [])
+
+
+def get_index_by_name(session: Session, table_name: str, index_name: str) -> str | None:
+    """Get an index by name."""
+    connection = session.connection()
+    inspector = inspect(connection)
+    indexes = inspector.get_indexes(table_name)
+    return next(
+        (
+            possible_index["name"]
+            for possible_index in indexes
+            if possible_index["name"]
+            and (
+                possible_index["name"] == index_name
+                or possible_index["name"].endswith(f"_{index_name}")
+            )
+        ),
+        None,
+    )

tests/components/recorder/test_v32_migration.py

@@ -91,6 +91,10 @@ async def test_migrate_times(
     )
     number_of_migrations = 5
 
+    def _get_states_index_names():
+        with session_scope(hass=hass) as session:
+            return inspect(session.connection()).get_indexes("states")
+
     with patch.object(recorder, "db_schema", old_db_schema), patch.object(
         recorder.migration, "SCHEMA_VERSION", old_db_schema.SCHEMA_VERSION
     ), patch.object(core, "StatesMeta", old_db_schema.StatesMeta), patch.object(
@@ -113,6 +117,8 @@ async def test_migrate_times(
         "homeassistant.components.recorder.Recorder._migrate_entity_ids",
     ), patch(
         "homeassistant.components.recorder.Recorder._post_migrate_entity_ids"
+    ), patch(
+        "homeassistant.components.recorder.Recorder._cleanup_legacy_states_event_ids"
     ):
         hass = await async_test_home_assistant(asyncio.get_running_loop())
         recorder_helper.async_initialize_recorder(hass)
@@ -132,11 +138,18 @@ async def test_migrate_times(
         await hass.async_block_till_done()
         await recorder.get_instance(hass).async_block_till_done()
 
+        states_indexes = await recorder.get_instance(hass).async_add_executor_job(
+            _get_states_index_names
+        )
+        states_index_names = {index["name"] for index in states_indexes}
+
         await hass.async_stop()
         await hass.async_block_till_done()
 
         dt_util.DEFAULT_TIME_ZONE = ORIG_TZ
 
+    assert "ix_states_event_id" in states_index_names
+
     # Test that the duplicates are removed during migration from schema 23
     hass = await async_test_home_assistant(asyncio.get_running_loop())
     recorder_helper.async_initialize_recorder(hass)
@@ -186,13 +199,20 @@ async def test_migrate_times(
         with session_scope(hass=hass) as session:
             return inspect(session.connection()).get_indexes("events")
 
-    indexes = await recorder.get_instance(hass).async_add_executor_job(
+    events_indexes = await recorder.get_instance(hass).async_add_executor_job(
         _get_events_index_names
     )
-    index_names = {index["name"] for index in indexes}
+    events_index_names = {index["name"] for index in events_indexes}
 
-    assert "ix_events_context_id_bin" in index_names
-    assert "ix_events_context_id" not in index_names
+    assert "ix_events_context_id_bin" in events_index_names
+    assert "ix_events_context_id" not in events_index_names
+
+    states_indexes = await recorder.get_instance(hass).async_add_executor_job(
+        _get_states_index_names
+    )
+    states_index_names = {index["name"] for index in states_indexes}
+
+    assert "ix_states_event_id" not in states_index_names
 
     await hass.async_stop()
     dt_util.DEFAULT_TIME_ZONE = ORIG_TZ