Re: [HACKERS] Re: Multi field hash indexes

Hannu Krosing writes:
> It can be complicated (especially for extensible hashing) but the
> theory
> for this seems to be on in the database handbooks under the name of
> 'segmented hash' or some like fancy name.
>
> The trick is to hash each field separately and then have a concatenation
>
> of the hash values.

More or less.

> so assuming that for fields (a,b,c) values (120, 'friday', 3.1415927)
> hash
> to 'aa', 'bb', 'cc' the hash value of the whole tuple will be 'aabbcc'

I had a research project on this several years ago and we found that all
these multidimensional hash trees have one or the other problem. But one
index type named Balanced Multidimensional Hash Tree (from the top of my
head) performed excellently by combining hash and tree structures.

Michael

--
Dr. Michael Meskes, Project-Manager    | topsystem Systemhaus GmbH
meskes@topsystem.de                    | Europark A2, Adenauerstr. 20
meskes@debian.org                      | 52146 Wuerselen
Go SF49ers! Go Rhein Fire!             | Tel: (+49) 2405/4670-44
Use Debian GNU/Linux!                  | Fax: (+49) 2405/4670-10