Про php не знаю, к сожалению, но java XSLT-Processor'ы (Xalan, Saxon) не парсят xml в DOM при трансформации, соответственно указанные объемы могут перелопатить довольно быстро (тут больше, на мой взгляд, зависит собственно от xsl-преобразования, т.е. оно само по себе может быть написано неэффективно)

1024и саксон и ксалан судя по документации парсят в дом.


Наличие класса в Xalan и Saxon ни о чем Вам не говорит? Да, есть и DOMSource, но это не отменяет возможности НЕ строить DOM

Вот еще цитатка из документации на Saxon (старый, правда)
The SAXON API: comparison with SAX and DOM
There are two standard APIs for processing XML documents: the SAX interface, and the DOM. SAX (see http://www.megginson.com/SAX/index.html) is an event-driven interface in which the parser reports things such as start and end tags to the application as they are encountered, while the Document Object Model (DOM) (see http://www.w3.org/dom is a navigational interface in which the application can roam over the document in memory by following relationships between its nodes. Another API, JDOM, is similar in concept to DOM but provides a lighter-weight API that is more closely integrated with the standard Java 2 classes.

SAXON offers a higher-level processing model than either SAX or DOM. It allows applications to be written using a rule-based design pattern, in which your application consists of a set of rules of the form "when this condition is encountered, do this processing". It is an event-condition-action model in which the events are the syntactic constructs of XML, the conditions are XSLT-compatible patterns, and the actions are Java methods. Further, the action taken when these rules are fired may include evaaluation of XPath expressions, providing a higher-level access mechanism than raw navigation of the tree.

If you are familiar with SAX, some of the differences in SAXON are:

You can provide a separate handler for each element type (or other node), making your application more modular
SAXON supplies context information to your application, so you can find out, for example, the parent element of the one you are currently processing
SAXON provides facilities for organizing the output of your application, allowing you to direct different parts of the output to different files. SAXON is a particularly convenient tool for splitting a large document into page-sized chunks for viewing, or into individual records for storing in a relational or object database.
SAXON allows you to register your preferred SAX-compliant XML parser; you do not need to hard-code the name of the parser into your application or supply it each time on the command line. SAXON also works with several DOM implementations.
SAXON extends the SAX InputSource class allowing you to specify a file name as the source of input.
1024
SAX это Simple API for XML, по сути просто считывание файла сверху вниз и вызывание пользовательской функции на каждый нод/атрибут. Никакого хсл
Спасибо, я тоже знаю, что 2*2=4