migration_manager: also reload schema on enabling digest_insensitive_…

…to_expiry

Currently, when said feature is enabled, we recalcuate the schema
digest. But this feature also influences how table versions are
calculated, so it has to trigger a recalculation of all table versions,
so that we can guarantee correct versions.
Before, this used to happen by happy accident. Another feature --
table_digest_insensitive_to_expiry -- used to take care of this, by
triggering a table version recalulation. However this feature only takes
effect if digest_insensitive_to_expiry is also enabled. This used to be
the case incidently, by the time the reload triggered by
table_digest_insensitive_to_expiry ran, digest_insensitive_to_expiry was
already enabled. But this was not guaranteed whatsoever and as we've
recently seen, any change to the feature list, which changes the order
in which features are enabled, can cause this intricate balance to
break.
This patch makes digest_insensitive_to_expiry also kick off a schema
reload, to eliminate our dependence on (unguaranteed) feature order, and
to guarantee that table schemas have a correct version after all features
are enabled.

Fixes: scylladb#16004

service/migration_manager.cc

@@ -103,19 +103,20 @@ void migration_manager::init_messaging_service()
             return db::schema_tables::recalculate_schema_version(_sys_ks, _storage_proxy.container(), _feat);
         });
     };
+    auto reload_schema_in_bg = [this] {
+        (void) with_gate(_background_tasks, [this] {
+            return reload_schema();
+        });
+    };
 
     if (this_shard_id() == 0) {
         _feature_listeners.push_back(_feat.view_virtual_columns.when_enabled(update_schema));
-        _feature_listeners.push_back(_feat.digest_insensitive_to_expiry.when_enabled(update_schema));
+        _feature_listeners.push_back(_feat.digest_insensitive_to_expiry.when_enabled(reload_schema_in_bg));
         _feature_listeners.push_back(_feat.cdc.when_enabled(update_schema));
         _feature_listeners.push_back(_feat.per_table_partitioners.when_enabled(update_schema));
 
         if (!_feat.table_digest_insensitive_to_expiry) {
-            _feature_listeners.push_back(_feat.table_digest_insensitive_to_expiry.when_enabled([this] {
-                (void) with_gate(_background_tasks, [this] {
-                    return reload_schema();
-                });
-            }));
+            _feature_listeners.push_back(_feat.table_digest_insensitive_to_expiry.when_enabled(reload_schema_in_bg));
         }
     }