Fix cpu thrashing during purge after all legacy events were removed (#89923)

* Fix cpu thrashing during purge after all legacy events were removed

We now remove the the index of of event ids on the states table when its
all NULLs to save space. The purge path needs to avoid checking for legacy
rows to purge if the index has been removed since it will result in a full
table scan each purge cycle that will always find no legacy rows to purge

* one more place

* drop the key constraint as well

* fixes

* more sqlite

tests/components/recorder/test_purge.py

@@ -10,7 +10,7 @@ from sqlalchemy.exc import DatabaseError, OperationalError
 from sqlalchemy.orm.session import Session
 
 from homeassistant.components import recorder
-from homeassistant.components.recorder import Recorder
+from homeassistant.components.recorder import Recorder, migration
 from homeassistant.components.recorder.const import (
     SQLITE_MAX_BIND_VARS,
     SupportedDialect,
@@ -1726,6 +1726,18 @@ async def test_purge_can_mix_legacy_and_new_format(
 ) -> None:
     """Test purging with legacy a new events."""
     instance = await async_setup_recorder_instance(hass)
+    await async_wait_recording_done(hass)
+    # New databases are no longer created with the legacy events index
+    assert instance.use_legacy_events_index is False
+
+    def _recreate_legacy_events_index():
+        """Recreate the legacy events index since its no longer created on new instances."""
+        migration._create_index(instance.get_session, "states", "ix_states_event_id")
+        instance.use_legacy_events_index = True
+
+    await instance.async_add_executor_job(_recreate_legacy_events_index)
+    assert instance.use_legacy_events_index is True
+
     utcnow = dt_util.utcnow()
     eleven_days_ago = utcnow - timedelta(days=11)
     with session_scope(hass=hass) as session:

tests/components/recorder/test_v32_migration.py

@@ -142,6 +142,7 @@ async def test_migrate_times(
             _get_states_index_names
         )
         states_index_names = {index["name"] for index in states_indexes}
+        assert recorder.get_instance(hass).use_legacy_events_index is True
 
         await hass.async_stop()
         await hass.async_block_till_done()
@@ -212,7 +213,12 @@ async def test_migrate_times(
     )
     states_index_names = {index["name"] for index in states_indexes}
 
-    assert "ix_states_event_id" not in states_index_names
+    # sqlite does not support dropping foreign keys so the
+    # ix_states_event_id index is not dropped in this case
+    # but use_legacy_events_index is still False
+    assert "ix_states_event_id" in states_index_names
+
+    assert recorder.get_instance(hass).use_legacy_events_index is False
 
     await hass.async_stop()
     dt_util.DEFAULT_TIME_ZONE = ORIG_TZ