BRIN (Block Range) Indices look really interesting.

Instead of storing the whole B-Tree (and spending time updating it) just store summary of ranges (pages).

This for example, would be great for a time series database that is write heavy but not read as often.

I found these benchmarks here explaining the differences:

http://www.depesz.com/2014/11/22/waiting-for-9-5-brin-block-...

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Creating 650MB tables:

   * btree: 626.859 ms.
   * brin: 208.754 ms

(3x speedup)

Updating 30% of values:

   * btree: 8398.461 ms.
   * brin: 1398.711 ms.

(4x speedup)

Extra bonus:

   * size of btree index: 28MB
   * size of brin: 64kb

Search (for a range):

  $ select count(*) from table where id between 600000::int8 and 650000::int8;
    * btree between: 9.574 ms
    * brin between: 21.090 ms

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