PostgreSQL
Indexes in PostgreSQL — 8 (RUM)
Although the authors claim that gin is a powerful genie, the theme of drinks has eventually won: next-generation GIN has been called RUM.
Indexes in PostgreSQL — 7 (GIN)
Gin stands for Generalized Inverted Index and should be considered as a genie, not a drink.
Indexes in PostgreSQL — 6 (SP-GiST)
SP-GiST is suitable for structures where the space can be recursively split into non-intersecting areas. This class comprises quadtrees, k-dimensional trees (k-D trees), and radix trees.
Indexes in PostgreSQL — 5 (GiST)
GiST is an abbreviation of «generalized search tree». This is a balanced search tree, just like «b-tree» discussed earlier.