Don't update the reference index while deleting it

The rebuild_reference_index management command starts by
deleting the entire ReferenceIndex table.

In Wagtail versions 4.1 and 4.2, all models are tracked in the
reference index. Unfortunately this also includes the
ReferenceIndex model itself. This is changed in 5.0 to only track certain Wagtail-related models [0].

This means that when rebuild_reference_index runs in versions
4.1 or 4.2, and deletes the ReferenceIndex table, it runs the code that checks whether ReferenceIndex instances have any
references.

If the index contains a large number of references (as could
happen if an upgrade to 4.1 built an index for a non-Wagtail
model), this process becomes extremely slow. There's no need
for the rebuild_reference_index command to update the index
when deleting it, so this can be significantly optimized by
disabling auto update here.

[0] https://docs.wagtail.org/en/stable/releases/5.0.html#referenceindex-no-longer-tracks-models-used-outside-of-wagtail

CHANGELOG.txt

@@ -123,6 +123,7 @@ Changelog
  * Maintenance: Migrate away from using the `"wagtailadmin/shared/field_as_li.html"` template include (Storm Heg)
  * Maintenance: Deprecate `wagtail.contrib.modeladmin` (Sage Abdullah)
  * Maintenance: Upgrade documentation theme `sphinx_wagtail_theme` to v6.1.1 which includes multiple styling fixes and always visible code copy buttons (LB (Ben) Johnston)
+ * Maintenance: Don't update the reference index while deleting it (Andy Chosak)
 
 
 5.0.2 (21.06.2023)

docs/releases/5.1.md

@@ -169,6 +169,7 @@ This feature was developed by Aman Pandey as part of the Google Summer of Code p
  * Remove unused snippets _header_with_history.html template (Thibaud Colas)
  * Migrate away from using the `"wagtailadmin/shared/field_as_li.html"` template include (Storm Heg)
  * Upgrade documentation theme `sphinx_wagtail_theme` to v6.1.1 which includes multiple styling fixes and always visible code copy buttons (LB (Ben) Johnston)
+ * Don't update the reference index while deleting it (Andy Chosak)
 
 ## Upgrade considerations
 

wagtail/management/commands/rebuild_references_index.py

@@ -3,6 +3,7 @@ from django.core.management.base import BaseCommand
 from django.db import transaction
 
 from wagtail.models import ReferenceIndex
+from wagtail.signal_handlers import disable_reference_index_auto_update
 
 DEFAULT_CHUNK_SIZE = 1000
 
@@ -36,7 +37,8 @@ class Command(BaseCommand):
         self.write("Rebuilding reference index")
 
         with transaction.atomic():
-            ReferenceIndex.objects.all().delete()
+            with disable_reference_index_auto_update():
+                ReferenceIndex.objects.all().delete()
 
             for model in apps.get_models():
                 if not ReferenceIndex.is_indexed(model):