erp5_wendelin/DataArray += .gcOrphanedArrays

This new method helps to free storage space of a Wendelin instance
in case 'DataArray.setArray(None)' has been called before.

Previously assigned ZBigArrays are orphaned (no longer related
to any other object). In order to free some storage space, we can
therefore remove them from the database by explicitly garbage
collecting them.

bt5/erp5_wendelin/DocumentTemplateItem/portal_components/document.erp5.DataArray.py

 # -*- coding: utf-8 -*-
 ##############################################################################
 #
-# Copyright (c) 2015 Nexedi SA and Contributors. All Rights Reserved.
+# Copyright (c) 2015-2024 Nexedi SA and Contributors. All Rights Reserved.
 #                    Ivan Tyagov <ivan@nexedi.com>
+#                    Levin Zimmermann <levin.zimmermann@nexedi.com>
 #
 # This program is free software: you can Use, Study, Modify and Redistribute
 # it under the terms of the GNU General Public License version 3, or (at your
@@ -153,6 +154,31 @@ class DataArray(BigFile):
     # return default view
     return self.view()
 
+  def gcOrphanedArrays(self):
+    """
+      If 'setArray(None)' has been called, the previously assigned
+      ZBigArrays are orphaned (no longer related to any other object).
+      In order to free some storage space, we can therefore remove
+      them from the database by explicitly garbage collecting them.
+
+      Beware: calling this breaks ZODB undo functionality.
+    """
+    conn = self._p_jar
+    storage = conn.db().storage
+    self._p_activate()
+    oid, tid = self._p_oid, self._p_serial
+    is_orphan = self.getArray() is None
+    while 1:
+      data = storage.loadBefore(oid, tid)
+      if not data:
+        break
+      state = conn.oldstate(self, data[1])
+      array = state['array']
+      if is_orphan and array:  # GC current ZBigArray
+        self.Base_deleteZBigArray(array)
+      is_orphan = array is None
+      tid = data[1]
+
   # FIXME this duplicates a lot of code from ERP5's BigFile
   # -> TODO reuse BigFile streaming capability without copying its code
   def _range_request_handler(self, REQUEST, RESPONSE):