Re: "Big O" notation for postgres?

On Wed, May 21, 2008 at 10:10 AM, H. Hall <hhall1001@reedyriver.com> wrote:
> Does anyone know if there is a source that provides "Big O" notation for
> postgres's aggregate functions and operations?  For example is count(*) =
> O(1) or O(n)?

I don't know of any document containing the complexity of each
aggregate, but it's sometimes left as a comment in the souce code.

IIRC, COUNT (non-distinct) is currently O(n), where n also includes
evaluation of tuples not represented in the final count (due to
Postgres' MVCC design).

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