Question

I have been working on optimizing my Postgres databases recently, and traditionally, I’ve only ever use B-Tree indexes. However, I saw that GiST indexes suport non-unique, multicolumn indexes, in the Postgres 8.3 documentation.

I couldn’t, however, see what the actual difference between them is. I was hoping that my fellow coders might beable to explain, what the pros and cons between them are, and more importantly, the reasons why I would use one over the other?

Answer 1

In a nutshell: B-Tree indexes perform better, but GiST indexes are more flexible. Usually, you want B-Tree indexes if they’ll work for your data type. There was a recent post on the PG lists about a huge performance hit for using GiST indexes; they’re expected to be slower than B-Trees (such is the price of flexibility), but not that much slower… work is, as you might expect, ongoing.

From a post by Tom Lane, a core PostgreSQL developer:

The main point of GIST is to be able to index queries that simply are not indexable in btree. … One would fully expect btree to beat out GIST for btree-indexable cases. I think the significant point here is that it’s winning by a factor of a couple hundred; that’s pretty awful, and might point to some implementation problem.