8.1

• The shared buffer cache used to hold database data was redesigned for better concurrent use. This change is the major reason 8.1 is the earliest PostgreSQL version with good scalability.
• Bitmap scans allow combining multiple single-column indexes for queries that reference more than one column. This decreases the need to create computationally expensive multi-column indexes on tables.
• Autovacuum, formerly a module that had to be explicitly loaded, was integrated into the main server (but not started by default).
• Table partitioning is improved to allow skipping partitions that can't possibly satisfy a query.
• Indexes are automatically used for MIN() and MAX() queries.