Good to know.
So the issue is with my attempt to transform a 300MB document, not an issue
with BaseX itself.
You may be able to save lots of time if you manage to rewrite the XSLT script to XQuery (Update). Here’s a script that creates an element with 1 million nodes, which are immediately deleted again. It takes less than 1 second:
<a>{ (1 to 1000000) ! <b/> }</a> update { delete node ./b }
Best, Christian