$PostgreSQL: pgsql/src/backend/access/hash/README,v 1.4 2003/11/29 19:51:40 pgsql Exp $

This directory contains an implementation of hash indexing for Postgres.

$PostgreSQL: pgsql/src/backend/access/hash/README,v 1.5 2007/01/09 07:30:49 tgl Exp $

This directory contains an implementation of hash indexing for Postgres. Most

of the core ideas are taken from Margo Seltzer and Ozan Yigit, A New Hashing

Package for UNIX, Proceedings of the Winter USENIX Conference, January 1991.

(Our in-memory hashtable implementation, src/backend/utils/hash/dynahash.c,

also relies on some of the same concepts; it is derived from code written by

Esmond Pitt and later improved by Margo among others.)

A hash index consists of two or more "buckets", into which tuples are

placed whenever their hash key maps to the bucket number. The