Add option to disable syncing to disk

Disabling syncing increases the risk of data loss when the system crashes or power fails. On the positive it can increase the performance to a great extent.

radicale/config.py

@@ -58,6 +58,7 @@ INITIAL_CONFIG = {
         "type": "multifilesystem",
         "filesystem_folder": os.path.expanduser(
             "~/.config/radicale/collections"),
+        "fsync": "True",
         "hook": ""},
     "logging": {
         "config": "/etc/radicale/logging",

radicale/storage.py

@@ -393,10 +393,11 @@ class Collection(BaseCollection):
                                  delete=False, prefix=".Radicale.tmp-")
         try:
             yield tmp
-            if os.name == "posix" and hasattr(fcntl, "F_FULLFSYNC"):
-                fcntl.fcntl(tmp.fileno(), fcntl.F_FULLFSYNC)
-            else:
-                os.fsync(tmp.fileno())
+            if self.configuration.getboolean("storage", "fsync"):
+                if os.name == "posix" and hasattr(fcntl, "F_FULLFSYNC"):
+                    fcntl.fcntl(tmp.fileno(), fcntl.F_FULLFSYNC)
+                else:
+                    os.fsync(tmp.fileno())
             tmp.close()
             os.rename(tmp.name, path)
         except:
@@ -413,13 +414,15 @@ class Collection(BaseCollection):
                 return file_name
         raise FileExistsError(errno.EEXIST, "No usable file name found")
 
-    @staticmethod
-    def _sync_directory(path):
+    @classmethod
+    def _sync_directory(cls, path):
         """Sync directory to disk.
 
         This only works on POSIX and does nothing on other systems.
 
         """
+        if not cls.configuration.getboolean("storage", "fsync"):
+            return
         if os.name == "posix":
             fd = os.open(path, 0)
             try: