Don't use TRUNCATE in functional unittests.

This is because we have multiple open storages holding table locks so we
livelock on each other.

CHANGES.txt

@@ -44,8 +44,12 @@
   Jacobs.
 
 - PostgreSQL: ``zodbconvert --clear`` should be much faster when the
-  destination is a PostgreSQL schema containing lots of data. Partial
-  fix for `issue 16`_ reported by Chris McDonough.
+  destination is a PostgreSQL schema containing lots of data. *NOTE*:
+  There can be no other open RelStorage connections to the destination,
+  or any PostgreSQL connection in general that might be holding locks
+  on the RelStorage tables, or ``zodbconvert`` will block indefinitely
+  waiting for the locks to be release. Partial fix for `issue 16`_
+  reported by Chris McDonough.
 
 .. _`PR 18`: https://github.com/zodb/relstorage/pull/18/
 .. _`PR 20`: https://github.com/zodb/relstorage/pull/20

relstorage/adapters/schema.py

@@ -886,9 +886,16 @@ def update_schema(self, cursor, tables):
 
     _zap_all_tbl_stmt = 'DELETE FROM %s'
 
-    def zap_all(self, reset_oid=True):
-        """Clear all data out of the database."""
-        stmt = self._zap_all_tbl_stmt
+    def zap_all(self, reset_oid=True, slow=False):
+        """
+        Clear all data out of the database.
+
+        :keyword bool slow: If True (*not* the default) then database
+            specific optimizations will be skipped and rows will simply be
+            DELETEd. This is helpful when other connections might be open and
+            holding some kind of locks.
+        """
+        stmt = self._zap_all_tbl_stmt if not slow else AbstractSchemaInstaller._zap_all_tbl_stmt
 
         def callback(_conn, cursor):
             existent = set(self.list_tables(cursor))

relstorage/storage.py

@@ -362,12 +362,12 @@ def _with_store(self, f, *args, **kw):
             log.info("Reconnected.")
             return f(self._store_conn, self._store_cursor, *args, **kw)
 
-    def zap_all(self, reset_oid=True):
+    def zap_all(self, **kwargs):
         """Clear all objects and transactions out of the database.
 
         Used by the test suite and the ZODBConvert script.
         """
-        self._adapter.schema.zap_all(reset_oid=reset_oid)
+        self._adapter.schema.zap_all(**kwargs)
         self._rollback_load_connection()
         self._cache.clear()
 

relstorage/tests/reltestbase.py

@@ -698,7 +698,7 @@ def checkPackBrokenPickle(self):
         # on whether the accelerated implementation is in use. Also ,the pure-python
         # version on PyPy can raise IndexError
         from zodbpickle.pickle import UnpicklingError as pUnpickErr
-        unpick_errs = (pUnpickErr,IndexError)
+        unpick_errs = (pUnpickErr, IndexError)
         try:
             from zodbpickle.fastpickle import UnpicklingError as fUnpickErr
         except ImportError:
@@ -709,7 +709,7 @@ def checkPackBrokenPickle(self):
 
         self._dostoreNP(self._storage.new_oid(), data=b'brokenpickle')
         self.assertRaises(unpick_errs, self._storage.pack,
-            time.time() + 10000, referencesf)
+                          time.time() + 10000, referencesf)
 
     def checkBackwardTimeTravelWithoutRevertWhenStale(self):
         # If revert_when_stale is false (the default), when the database
@@ -743,7 +743,7 @@ def checkBackwardTimeTravelWithoutRevertWhenStale(self):
                 transaction.commit()
                 self.assertTrue('beta' in r)
 
-                c._storage.zap_all(reset_oid=False)
+                c._storage.zap_all(reset_oid=False, slow=True)
                 c._storage.copyTransactionsFrom(fs)
 
                 fs.close()
@@ -794,7 +794,7 @@ def checkBackwardTimeTravelWithRevertWhenStale(self):
                 transaction.commit()
                 self.assertTrue('beta' in r)
 
-                c._storage.zap_all(reset_oid=False)
+                c._storage.zap_all(reset_oid=False, slow=True)
                 c._storage.copyTransactionsFrom(fs)
 
                 fs.close()