> -----Original Message----- > From: pgsql-general-owner@xxxxxxxxxxxxxx [mailto:pgsql-general- > owner@xxxxxxxxxxxxxx] On Behalf Of Alvaro Herrera > Sent: Monday, January 12, 2009 12:41 PM > To: Bruno Lavoie > Cc: PostgreSQL > Subject: Re: Indexing columns with low cardinality: > persistentbitmap indexes? > > Bruno Lavoie escribió: > > Hello, > > > > I have a column with a small number of distinct values, indexing this > > one with a standard BTree is useless. How do I can index this column > > efficiently? I searched and it seems that pg doesn't support the > > creation of persistent bitmap indexes... > > It doesn't. > > > Is that feature planned in next releases of pg? > > There are some efforts to get it done, but don't hold your breath (it > won't be in 8.4 either, as it has major problems currently.) Here is an interesting experiment: Application of Bitmap Index to Information Retrieval. K. Fujioka, Y. Uematsu, and M. Onizuka. WWW 2008 Source: [ACM] Synopsis: This paper proposes a hierarchical structure called HS-bitmap index to represent document-term matrix. The authors implemented their data structure on PostgreSQL and observed it to perform better than an inverted index. A short-coming might be that HS-bitmap index takes more space than the inverted index even after compression. Note this work makes use of PostgreSQL but is unrelated to the on-going work of implementing bitmap index in PostgreSQL. http://portal.acm.org/citation.cfm?doid=1367497.1367680 Here is the research page where I found the above: http://www-users.cs.umn.edu/~kewu/annotated.html -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
