I was able to reproduce the slow down page responding only when saving the large content placed in email.rtf file and only in IE.
Please, note that there are five main reasons responsible for the slow editor performance when editing large XHTML/HTML files (>100KB).
Reason 1: The undo/redo mechanism and other maintenance code that
ensures the smooth user experience - it gets increasingly cumbersome
and time consuming for the browser to execute it if huge content is in
Reason 2: The fact that most of the editor functionality is implemented
to native compiled code.
Reason 3: test the performance only when <compilation debug="false"
in your web.config. When it is true, the MS AJAX debugging code kicks
in and causes a severe performance hit on the client-side.
Remove the RadEditor modules (you have already done this suggestion), e.g.
<telerik:radeditor runat="server" ID="RadEditor1">
<telerik:EditorModule Visible="false" />
Reason 5 (valid when switching between the view modes or submitting the
content): In difference with the TextBox control which does not process
the content when submitting it to the server, the RadEditor runs
content filters which validate the non well formatted content and make
it XHTML compliant. Right now the editor runs more than 11 content
filters. These filters run regular expressions which parse and validate
the large content, which slow down the content submission to the
server. You can disable the filters by setting ContentFilters property to None, e.g.
<telerik:RadEditor ID="RadEditor1" ContentFilters="None" runat="server"></telerik:RadEditor>
The policy behind all radcontrols is that they should be
cross-browser and should offer similar experience over different
browsers and OS-es. At present the editor supports IE under Windows,
Mozilla Firefox under all platforms, Opera under all platforms and
Safari under Mac. Such cross-browser functionality is possible only
Being cross-browser is a top priority, and thus at present it rules out changing the editor's technology.
We are constantly working on improving the speed, but the browsers do
have their limits, and it is not hard to reach them when editing large
content in the editor.
You can find more information in the following KB article: RadEditor loads slowly (high CPU utilization)
strongly suggest avoiding loading or saving 100K of content into the
editor in a real-world scenario (that is, other than for test purposes)
- as an actual user will not get a good experience if they have to deal
with editing 100K of HTML on a single go.
the Telerik team