Do casual reads only on Galera

src/pretix/base/views/async.py

@@ -9,7 +9,6 @@ from django.shortcuts import redirect, render
 from django.utils.translation import ugettext as _
 
 from pretix.celery_app import app
-from pretix.helpers.database import casual_reads
 
 logger = logging.getLogger('pretix.base.async')
 
@@ -32,11 +31,10 @@ class AsyncAction:
             return JsonResponse(data)
         else:
             if res.ready():
-                with casual_reads():
+                if res.successful() and not isinstance(res.info, Exception):
-                    if res.successful() and not isinstance(res.info, Exception):
+                    return self.success(res.info)
-                        return self.success(res.info)
+                else:
-                    else:
+                    return self.error(res.info)
-                        return self.error(res.info)
             return redirect(self.get_check_url(res.id, False))
 
     def get_success_url(self, value):
@@ -66,25 +64,24 @@ class AsyncAction:
             'ready': ready
         }
         if ready:
-            with casual_reads():
+            if res.successful() and not isinstance(res.info, Exception):
-                if res.successful() and not isinstance(res.info, Exception):
+                smes = self.get_success_message(res.info)
-                    smes = self.get_success_message(res.info)
+                if smes:
-                    if smes:
+                    messages.success(self.request, smes)
-                        messages.success(self.request, smes)
+                # TODO: Do not store message if the ajax client states that it will not redirect
-                    # TODO: Do not store message if the ajax client states that it will not redirect
+                # but handle the mssage itself
-                    # but handle the mssage itself
+                data.update({
-                    data.update({
+                    'redirect': self.get_success_url(res.info),
-                        'redirect': self.get_success_url(res.info),
+                    'message': str(self.get_success_message(res.info))
-                        'message': str(self.get_success_message(res.info))
+                })
-                    })
+            else:
-                else:
+                messages.error(self.request, self.get_error_message(res.info))
-                    messages.error(self.request, self.get_error_message(res.info))
+                # TODO: Do not store message if the ajax client states that it will not redirect
-                    # TODO: Do not store message if the ajax client states that it will not redirect
+                # but handle the mssage itself
-                    # but handle the mssage itself
+                data.update({
-                    data.update({
+                    'redirect': self.get_error_url(),
-                        'redirect': self.get_error_url(),
+                    'message': str(self.get_error_message(res.info))
-                        'message': str(self.get_error_message(res.info))
+                })
-                    })
         return data
 
     def get_result(self, request):
@@ -93,11 +90,10 @@ class AsyncAction:
             return JsonResponse(self._return_ajax_result(res, timeout=0.25))
         else:
             if res.ready():
-                with casual_reads():
+                if res.successful() and not isinstance(res.info, Exception):
-                    if res.successful() and not isinstance(res.info, Exception):
+                    return self.success(res.info)
-                        return self.success(res.info)
+                else:
-                    else:
+                    return self.error(res.info)
-                        return self.error(res.info)
             return render(request, 'pretixpresale/waiting.html')
 
     def success(self, value):

src/pretix/helpers/database.py

@@ -1,7 +1,6 @@
 import contextlib
 
-from django.conf import settings
+from django.db import transaction
-from django.db import connection, transaction
 
 
 class DummyRollbackException(Exception):
@@ -29,38 +28,9 @@ def rolledback_transaction():
         raise Exception('Invalid state, should have rolled back.')
 
 
-if 'mysql' in settings.DATABASES['default']['ENGINE'] and settings.DATABASE_IS_GALERA:
+@contextlib.contextmanager
-
+def casual_reads():
-    @contextlib.contextmanager
+    """
-    def casual_reads():
+    Kept for backwards compatibility.
-        """
+    """
-        When pretix runs with a MySQL galera cluster as a database backend, we can run into the
+    yield
-        following problem:
-
-        * A celery thread starts a transaction, creates an object and commits the transaction.
-          It then returns the object ID into celery's result store (e.g. redis)
-
-        * A web thread pulls the object ID from the result store, but cannot access the object
-          yet as the transaction is not yet committed everywhere.
-
-        This sets the wsrep_sync_wait variable to deal with this problem.
-
-        See also:
-
-        * https://mariadb.com/kb/en/mariadb/galera-cluster-system-variables/#wsrep_sync_wait
-
-        * https://www.percona.com/doc/percona-xtradb-cluster/5.6/wsrep-system-index.html#wsrep_sync_wait
-        """
-        with connection.cursor() as cursor:
-            cursor.execute("SET @wsrep_sync_wait_orig = @@wsrep_sync_wait;")
-            cursor.execute("SET SESSION wsrep_sync_wait = GREATEST(@wsrep_sync_wait_orig, 1);")
-            try:
-                yield
-            finally:
-                cursor.execute("SET SESSION wsrep_sync_wait = @wsrep_sync_wait_orig;")
-
-else:
-
-    @contextlib.contextmanager
-    def casual_reads():
-        yield

src/pretix/settings.py

@@ -50,6 +50,14 @@ debug_fallback = "runserver" in sys.argv
 DEBUG = config.getboolean('django', 'debug', fallback=debug_fallback)
 
 db_backend = config.get('database', 'backend', fallback='sqlite3')
+DATABASE_IS_GALERA = config.getboolean('database', 'galera', fallback=False)
+if DATABASE_IS_GALERA and 'mysql' in db_backend:
+    db_options = {
+        'init_command': 'SET SESSION wsrep_sync_wait = 1;'
+    }
+else:
+    db_options = {}
+
 DATABASES = {
     'default': {
         'ENGINE': 'django.db.backends.' + db_backend,
@@ -58,10 +66,10 @@ DATABASES = {
         'PASSWORD': config.get('database', 'password', fallback=''),
         'HOST': config.get('database', 'host', fallback=''),
         'PORT': config.get('database', 'port', fallback=''),
-        'CONN_MAX_AGE': 0 if db_backend == 'sqlite3' else 120
+        'CONN_MAX_AGE': 0 if db_backend == 'sqlite3' else 120,
+        'OPTIONS': db_options
     }
 }
-DATABASE_IS_GALERA = config.getboolean('database', 'galera', fallback=False)
 
 STATIC_URL = config.get('urls', 'static', fallback='/static/')