only avoid clobbering corrupt dbs that have some content

this logic can be triggered by connection failures that do not mean the file is corrupt,
so we don't want to lose data unnecessarily.

IPython/core/history.py

@@ -71,11 +71,18 b' else:'
     class OperationalError(Exception):
         "Dummy exception when sqlite could not be imported. Should never occur."
 
+# use 16kB as threshold for whether a corrupt history db should be saved
+# that should be at least 100 entries or so
+_SAVE_DB_SIZE = 16384
+
 @decorator
 def catch_corrupt_db(f, self, *a, **kw):
     """A decorator which wraps HistoryAccessor method calls to catch errors from
     a corrupt SQLite database, move the old database out of the way, and create
     a new one.
+
+    We avoid clobbering larger databases because this may be triggered due to filesystem issues,
+    not just a corrupt file.
     """
     try:
         return f(self, *a, **kw)
@@ -87,16 +94,23 b' def catch_corrupt_db(f, self, *a, **kw):'
                 self.hist_file = ':memory:'
                 self.log.error("Failed to load history too many times, history will not be saved.")
             elif os.path.isfile(self.hist_file):
-                # Try to move the file out of the way
-                base,ext = os.path.splitext(self.hist_file)
-                now = datetime.datetime.now().isoformat().replace(':', '.')
-                newpath = base + '-corrupt-' + now + ext
-                # don't clobber previous corrupt backups
-                for i in range(100):
-                    if not os.path.isfile(newpath):
-                        break
-                    else:
-                        newpath = base + '-corrupt-' + now + (u'-%i' % i) + ext
+                # move the file out of the way
+                base, ext = os.path.splitext(self.hist_file)
+                size = os.stat(self.hist_file).st_size
+                if size >= _SAVE_DB_SIZE:
+                    # if there's significant content, avoid clobbering
+                    now = datetime.datetime.now().isoformat().replace(':', '.')
+                    newpath = base + '-corrupt-' + now + ext
+                    # don't clobber previous corrupt backups
+                    for i in range(100):
+                        if not os.path.isfile(newpath):
+                            break
+                        else:
+                            newpath = base + '-corrupt-' + now + (u'-%i' % i) + ext
+                else:
+                    # not much content, possibly empty; don't worry about clobbering
+                    # maybe we should just delete it?
+                    newpath = base + '-corrupt' + ext
                 os.rename(self.hist_file, newpath)
                 self.log.error("History file was moved to %s and a new file created.", newpath)
             self.init_db()