Saxon

Environment: Saxon 11.1, JDK 8

After upgrading to Saxon 11.1 I noticed some slowdown and hotspots from new methods like ZenoString.concat Attached backtraces/callees from a yourkit sampling snapshot.

The transformation had a lot of:

• replace() function calls
• escape-html-uri() function calls
• element generation with xsl:attribute name="href" that needed escaping
  • so this affects serialization of all attributes matching net.sf.saxon.serialize.HTMLURIEscaper#isUrlAttribute

I worked around my problems by offloading to a Java extension function. The replace() calls I'm not sure about but for escape-html-uri() and associated XHTML serializer calls this seems like a regression.

• Test case: I had some URIs that were around 200 characters long but only 1 or 2 characters needed escaping.
• Up to and including Saxon 10 HTMLURIEscaper#reallyEscapeURL used a new FastStringBuffer(url.length() + 20);
• In Saxon 11.1 it seems to just initialize an empty UnicodeBuilder

HTMLURIEscaper#escapeURL is optimized for the common case of only ASCII characters so if we enter reallyEscapeURL it's clear that the resulting string will be at least the size of the input string, right?

But with the new string handling we start with an empty builder and it seems a lot of time is spent in growing the ArrayLists and the consolidation.

Maybe it makes sense to specialize HTMLURIEscaper#reallyEscapeURL ? Since it had a specialized pre-allocation already in previous versions.

This was the biggest hotspot I noticed so far relating to new string handling but I'm still going through other transformations in the next days so I'll update if I find anything similar.