Replication apparently now exists for PostGreSql but is fairly new and looks like it might still be less-than-ideal:

http://www.infocopter.com/know-how/postgres-replication.htm

http://www.geocities.com/mailsoftware42/db/#replication

Here is some information on PGSQL in particular (the command language) in case you were really asking about that:

http://www.commandprompt.com/ppbook/index.lxp?lxpwrap=c19610.htm

Here is a list of gotchas and a general FAQ (the second link may not display properly in IE, use a different browser)

http://sql-info.de/postgresql/postgres-gotchas.html

http://sql-info.de/postgresql/postfaq.html

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