Java as a technology is not native to Yahoo! The platform at Yahoo! was primarily C/C++ and PHP at the frontend (mostly). Java came through several acquisitions which were running Java stack, notably:

• 1998 Classic Games, Sprtasy
• 2002 Hotjobs
• 2003 Overture (Altavista)
• 2004 Kelkoo, Musimatch
   

Here are the raw bytes from the session:

• Tomcat + jboss efforts for securing them
• Mostly LAMP stack at Yahoo!
• Rate limiting using Apache modules 
• Runs apache in multiple process mode
• Y! data streams for keeping application specific stores and pushing data around (Yahoo’s proprietary message bus like implementation)
• Integration using JNI to C++ code using Swig for wrapper generation
• All security related code is in C++; helps maintain a single language code-base. Hence, wide JNI use from app tier
• Uses IPC Bridge for coarse grained calls to non-thread safe libraries (JNI has multi-threading issues)
• Group dedicated to creating JNI wrappers of native code
• JNI performance FUD
• Java to Native C++ code via JNI < 20 nano seconds (Cool!) compare this with Java to Java < 1 nano seconds. Big difference but nano seconds compared to network latencies of seconds
• String functions to native code via JNI take > 3ms coz of UTF-16 to UTF-8 character conversion issues
• JNI Multi-threading issues are solved by IPC bridge shared memory and TCP over loopback
• JSVC Apache commons daemon for loading privileged data during Tomcat startup and then running in low privilege mode
• Like Multi-process Apache, a new architecture for multi-process Tomcat being baked
• Software project management using Maven (Maven — awww!)
• Automatic builds using Cruise control and Hudson
• RPM-based software deployment to 100s of nodes