--- a/hgext3rd/evolve/stablerangecache.py	Mon Aug 27 00:28:19 2018 +0200
+++ b/hgext3rd/evolve/stablerangecache.py	Mon Aug 27 00:35:51 2018 +0200
@@ -225,7 +225,14 @@
     def _save(self, repo):
         try:
             return self._trysave(repo)
-        except sqlite3.OperationalError as exc:
+        except (sqlite3.OperationalError, sqlite3.IntegrityError) as exc:
+            # Catch error that may arise under stress
+            #
+            # operational error catch read-only and locked database
+            # IntegrityError catch Unique constraint error that may arise
+            if '_con' in vars(self):
+                del self._con
+            self._unsavedsubranges.clear()
             repo.ui.log('evoext-cache', 'error while saving new data: %s' % exc)
 
     def _trysave(self, repo):