[IronPython] Performance str.replace in Silverlight

Michael Foord michael at voidspace.org.uk
Thu May 27 09:41:28 PDT 2010

Hey guys,

I just tracked down a really nasty performance bug in our Silverlight 
application. It turned out that doing a simple string replace in a 400 
character string was taking 700ms. As we actually do two replaces and 
the text is usually substantially longer this was a real problem.

I fixed the problem by switching to explicitly calling the .NET 
String.Replace instead of str.replace, so it looks like an IronPython 
issue. It doesn't happen with *all* text, but it looks like non-ascii 
exacerbates the problem.

The particular text that triggered it was:

Die Neuanlage einer Welle muss auch zu Einträgen in der Tabelle 
dbo_tv_wellenwebsitesfirmenverbinder führen. Dabei werden die 
Zuordnungen aus der Vorwelle bei der Neuanlage einer neuen Welle 
einmalig übernommen. Jede Zeile der Vorwelle wird also kopiert und die 
Kopie erhält die Welle_uniqueID der neuen Welle. Die Verbindung zwischen 
Website_uniqueID <-> Firmen_uniqueID <-> FirmenAbrechnung_uniqueID 
bleibt somit erhalten.

The replace code was:

text = text.replace('\r\n', '\n').replace('\r', '\n')

The fix was:

text = String.Replace(text, '\r\n', '\n')
text = String.Replace(text, '\r', '\n')

All the best,

Michael Foord


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