Anyone know about how IndexTank's facets scale with the cardinality of the attribute? We tried using ElasticSearch's facet system for tags, but we have about 150k tags, and this does not play well with ES. (It's very stupid about how it caches them.)
IndexTank categories are not designed for the tags use case, and will not work properly. It's intended for a relatively small amount of categories for which each document has a single value. The amount of different values of a category can be large but the amount of categories cannot. If you want to implement something like tags, then each tag should be a category because you'll want more than a single tag per document. We were in the process of designing a new feature to support this kind of use cases, and maybe we'll start a branch to implement it and hopefully the community will colaborate.