for PostgreSQL questions specific to version 9.1.
PostgreSQL 9.1 is the version of PostgreSQL released in September of 2011, with expected end-of-life in September of 2016.
While the generic postgresql tag should probably be used with all PostgreSQL-related questions, this tag should also be used if the question pertains to features added in version 9.1, or if the question is about a problem seen while running version 9.1.