[1.6.x] Fixed #23089 -- Fixed transaction handling in two management commands.

Previously, when createcachetable and flush operated on non-default
databases, they weren't atomic.

Also avoided transactional DDL and transactional truncates on databases
that don't support them (refs #22308).

Backport of 753a22a635, 0757e0f30d, and 6877a9d415 from master

django/core/management/commands/createcachetable.py

@@ -53,7 +53,7 @@ class Command(LabelCommand):
         for i, line in enumerate(table_output):
             full_statement.append('    %s%s' % (line, ',' if i < len(table_output)-1 else ''))
         full_statement.append(');')
-        with transaction.commit_on_success_unless_managed():
+        with transaction.atomic(using=db, savepoint=connection.features.can_rollback_ddl):
             curs = connection.cursor()
             try:
                 curs.execute("\n".join(full_statement))

django/core/management/commands/flush.py

@@ -28,8 +28,8 @@ class Command(NoArgsCommand):
            're-executed, and the initial_data fixture will be re-installed.')
 
     def handle_noargs(self, **options):
-        db = options.get('database')
-        connection = connections[db]
+        database = options.get('database')
+        connection = connections[database]
         verbosity = int(options.get('verbosity'))
         interactive = options.get('interactive')
         # The following are stealth options used by Django's internals.
@@ -63,7 +63,8 @@ Are you sure you want to do this?
 
         if confirm == 'yes':
             try:
-                with transaction.commit_on_success_unless_managed():
+                with transaction.atomic(using=database,
+                                        savepoint=connection.features.can_rollback_ddl):
                     cursor = connection.cursor()
                     for sql in sql_list:
                         cursor.execute(sql)
@@ -78,7 +79,7 @@ Are you sure you want to do this?
                 six.reraise(CommandError, CommandError(new_msg), sys.exc_info()[2])
 
             if not inhibit_post_syncdb:
-                self.emit_post_syncdb(verbosity, interactive, db)
+                self.emit_post_syncdb(verbosity, interactive, database)
 
             # Reinstall the initial_data fixture.
             if options.get('load_initial_data'):

django/db/backends/__init__.py

@@ -652,6 +652,9 @@ class BaseDatabaseFeatures(object):
     # supported by the Python driver
     supports_paramstyle_pyformat = True
 
+    # Can we roll back DDL in a transaction?
+    can_rollback_ddl = False
+
     def __init__(self, connection):
         self.connection = connection
 

django/db/backends/postgresql_psycopg2/base.py

@@ -49,6 +49,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_tablespaces = True
     supports_transactions = True
     can_distinct_on_fields = True
+    can_rollback_ddl = True
 
 class DatabaseWrapper(BaseDatabaseWrapper):
     vendor = 'postgresql'

django/db/backends/sqlite3/base.py

@@ -102,6 +102,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     can_combine_inserts_with_and_without_auto_increment_pk = False
     autocommits_when_autocommit_is_off = True
     atomic_transactions = False
+    can_rollback_ddl = True
     supports_paramstyle_pyformat = False
 
     @cached_property