Mastering PostgreSQL 12 - Third Edition

BRIN indexes

Block range indexes (BRINs) are of great practical use. All of the indexes we've discussed up until now need quite a lot of disk space. Although a lot of work has gone into shrinking GIN indexes and the like, they still need quite a lot of disk space because an index pointer is needed for each entry. So, if there are 10 million entries, there will be 10 million index pointers. Space is the main concern that's addressed by BRIN indexes. A BRIN does not keep an index entry for each tuple, but will store the minimum and the maximum value of 128 (default) blocks of data (1 MB). The index is therefore very small but lossy. Scanning the index will return more data than we asked for. PostgreSQL has to filter out these additional rows ...