One issue I’ve had in the back of my mind but haven’t really made explicit is the question of exactly how to deal with these oddball queries.

There’s query normalization—converting + and _ to spaces, converting curly quotes to straight quotes, and the like—which should do at least whatever normalization the indexer does. (Is there documentation on what normalization the indexer does do?)

Then there are more destructive/transformative techniques, like stripping quot and timestamps, that should perhaps only be used for suggestions (which can be rolled over into re-queries when the original gives zero results).

URL decoding is sort of in between the two, to me. It’s more transformative than straightening quotes, but probably preserves the original intent of the searcher.

And then there are the last ditch attempts to get something vaguely relevant, like converting all non-alphanumerics to spaces—which is a very good last ditch effort, but should only be used if the original and maybe other backoffs fail.

In theory I also like David’s idea of refactoring things so multiple query expansion profiles are possible. Of course multiple searches are expensive. But even if we can’t run too many queries per search, the ability to run different expanded queries for different classes of queries is cool. (e.g., one word query => aggressive expansion; 50 word query => minimal expansion; 500 word query (see below!) => no expansion.)

In addition to identifying patterns and categories of searches that we can treat differently for analytics, it would make sense to do the same for actual queries. In our quest for non-zero results we shouldn’t favor recall over precision so much that we lose relevance.

One category I found was even crazier than I had anticipated was length. I don’t have the full details at hand at the moment, but out of 500K zero-result queries, there were thousands that were more than 100 characters long, and many that were over a thousand characters long. The longest were over 5000 characters. We should have a heuristic to not do any query expansion for queries longer than x characters, or z tokens or something. Doing OR expansion on hundreds of words—they often look like excerpts from books or articles—is a waste of our computational resources.

—Trey