Ролг ХупинВот, например, такое нашел в одной статье

авторB-Tree: The default for Postgres.
GIN: For JSONB and arrays. As inverted indexes, they contain an index entry for each word, with a compressed list of matching locations.
GiST : For full text search and geospatial datatypes. A GiST index is lossy, meaning that the index might produce false matches.
SP-GiST : For larger datasets with natural but uneven clustering
BRIN (Block Range Index) : For really large datasets that line up sequentially. E.g. orders might have a date column, and most of the time the entries for earlier orders appear earlier in the table.
Hash: The query planner will consider using a hash index whenever an indexed column is involved in a comparison using the = operator.

hash нельзя, он минует WAL

вот ещё:

о, ну клёво, в 9.5 разрабы их ещё не рекомендовали