Google has a huge codebase, which makes navigation a challenge using the default ctags/etags mechanism with Emacs or Vim --- any TAGS files generated is large enough that the default search mechanism will take a long time to complete. We could make every project build its own TAGS file (thereby reducing the size of the indices), but that would have been cumbersome. We decided instead to build a TAGS server (available on SourceForge) that would serve the index for the entire Google source base over the intranet for code browsing purposes, which has the benefit of speeding up code browsing dramatically as well as providing a way to look up any function anywhere in the code base.
Many open source projects have a significant amount of source code as well, and we hope that this enhancement to TAGS will be useful to the open source community.
Ken Ashcraft, Arthur Gleckler, Leandro Groisman, Piaw Na, Arun Sharma