On systems where the fsync system call is available, we now call

fsync when commiting transactions to make sure that transaction
data are written to physical storage immediately. There is circumstantial
evidence that database corruption has been caused due to problems with
delayed write of data after Zope has flushed transaction data.

Added logic to avoid writing empty transactions. It's imaginable that
some future application might want to write empty transactions to
capture transaction meta data. If this ever becomes an issue, then
this feature would have to be made optional.

src/ZODB/FileStorage.py

@@ -184,7 +184,7 @@
 #   may have a back pointer to a version record or to a non-version
 #   record.
 #
-__version__='$Revision: 1.32 $'[11:-2]
+__version__='$Revision: 1.33 $'[11:-2]
 
 import struct, time, os, bpthread, string, base64, sys
 from struct import pack, unpack
@@ -198,6 +198,9 @@ register_subsystem('ZODB FS')
 import BaseStorage
 from cPickle import Pickler, Unpickler
 
+try: from posix import fsync
+except: fsync=None
+
 z64='\0'*8
 
 def warn(message, *data):
@@ -667,10 +670,11 @@ class FileStorage(BaseStorage.BaseStorage):
         self._thl=23+len(u)+len(d)+len(e)
 
     def _finish(self, tid, u, d, e):
-        file=self._file
-        write=file.write
         tfile=self._tfile
         dlen=tfile.tell()
+        if not dlen: return # No data in this trans
+        file=self._file
+        write=file.write
         tfile.seek(0)
         id=self._serial
         user, desc, ext = self._ude
@@ -701,6 +705,10 @@ class FileStorage(BaseStorage.BaseStorage):
             file.seek(pos+16)
             write(' ')        
             file.flush()
+
+            if fsync is not None:
+                fsync(file.fileno())
+
         except:
             # Hm, an error occured writing out the data. Maybe the
             # disk is full. We don't want any turd at the end.
@@ -713,6 +721,7 @@ class FileStorage(BaseStorage.BaseStorage):
 
         self._vindex.update(self._tvindex)
 
+
     def undo(self, transaction_id):
         self._lock_acquire()
         try: