The thing is, there's not much documentation on where each index type would be applicable, what their upsides and downsides are in particular situations. For e

The thing is, there's not much documentation on where each index type would be applicable, what their upsides and downsides are in particular situations. For example, the hash index is (currently) not WAL-logged, which means it's not crash safe and not replicated. It also may have some concurrency issues, the resources are sparse on this one. The BRIN index should be ideal for situations where there is a huge storage of data (TBs) inserted in sequential order and rarely queried - a BRIN index for such a thing would be only a few MB in size. I say should because when I tried it on 9.5.0, the query planner kept ignoring the index. Both GIN and GIST indexes can be used for full text search (tsearch2), but GIN is faster for queries while GIST is smaller and faster for insertion. The SP-GIST index is so underdocumented that, when I wanted to try it out in a project, I could not even understand how it works and does it work correctly as a radix tree for strings. What's also somewhat underdocumented are the "operator classes" and which are and aren't implemented for different index types. I.e. a table of which index type can be used with which data type (and what exactly does such combination produce) would be great.