disable support for table & column comments

Otherwise, the Django test suite run time increases from < 1 hour to 6.5 hours.

Author: timgraham

README.md

@@ -104,6 +104,9 @@ using back to Cockroach Labs. To disable this, set
      later operation tries to modify the table before the asynchronous query
      finishes. A future version of CockroachDB [may fix this](https://github.com/cockroachdb/cockroach/issues/47137).
 
+- The `Field.db_comment` and `Meta.db_table_comment` options aren't supported
+  due to [poor performance](https://github.com/cockroachdb/cockroach/issues/95068).
+
 - Unsupported queries:
    - [Mixed type addition in SELECT](https://github.com/cockroachdb/django-cockroachdb/issues/19):
      `unsupported binary operator: <int> + <float>`

django_cockroachdb/features.py

@@ -49,6 +49,10 @@ class DatabaseFeatures(PostgresDatabaseFeatures):
     # PostgreSQL behaves the opposite.
     nulls_order_largest = False
 
+    # pg_catalog.obj_description is very slow:
+    # https://github.com/cockroachdb/cockroach/issues/95068
+    supports_comments = False
+
     @cached_property
     def introspected_field_types(self):
         return {

django_cockroachdb/introspection.py

@@ -1,9 +1,36 @@
 from django.db.backends.postgresql.introspection import (
-    DatabaseIntrospection as PostgresDatabaseIntrospection,
+    DatabaseIntrospection as PostgresDatabaseIntrospection, TableInfo,
 )
 
 
 class DatabaseIntrospection(PostgresDatabaseIntrospection):
     data_types_reverse = dict(PostgresDatabaseIntrospection.data_types_reverse)
     data_types_reverse[1184] = 'DateTimeField'  # TIMESTAMPTZ
     index_default_access_method = 'prefix'
+
+    def get_table_list(self, cursor):
+        # pg_catalog.obj_description is removed from this query to speed it up:
+        # https://github.com/cockroachdb/cockroach/issues/95068
+        """Return a list of table and view names in the current database."""
+        cursor.execute(
+            """
+            SELECT
+                c.relname,
+                CASE
+                    WHEN c.relispartition THEN 'p'
+                    WHEN c.relkind IN ('m', 'v') THEN 'v'
+                    ELSE 't'
+                END,
+                ''
+            FROM pg_catalog.pg_class c
+            LEFT JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace
+            WHERE c.relkind IN ('f', 'm', 'p', 'r', 'v')
+                AND n.nspname NOT IN ('pg_catalog', 'pg_toast')
+                AND pg_catalog.pg_table_is_visible(c.oid)
+        """
+        )
+        return [
+            TableInfo(*row)
+            for row in cursor.fetchall()
+            if row[0] not in self.ignored_tables
+        ]