PostgreSQL 16 introduces several features and improvements that enhance performance:

1. Query Planner Optimizations: It can now parallelize FULL and RIGHT joins, optimize aggregate functions with DISTINCT or ORDER BY, use incremental sorts for SELECT DISTINCT queries, and optimize window functions for better efficiency. Additionally, PostgreSQL 16 optimizes RIGHT and OUTER anti-joins.
2. Bulk Loading Improvements: Performance improvements in bulk loading using COPY are notable, with up to 300% performance enhancement in some scenarios. PostgreSQL 16 also supports load balancing in libpq clients and introduces CPU acceleration using SIMD in both x86 and ARM architectures. This leads to performance gains in processing ASCII and JSON strings and in array and subtransaction searches.
3. Logical Replication Enhancements: PostgreSQL 16 allows logical replication from a standby instance and introduces performance improvements such as using parallel workers for large transactions and B-tree indexes instead of sequential scans for tables without a primary key.
4. Developer Experience: New syntax from the SQL/JSON standard is added, including JSON_ARRAY(), JSON_ARRAYAGG(), and IS JSON. Underscores for thousands separators in numbers and non-decimal integer literals are supported. The psql commands are enhanced for a better developer experience.
5. Monitoring Improvements: New I/O metrics are available via pg_stat_io for granular analysis of I/O access patterns. The pg_stat_all_tables view now includes a timestamp for the last scan of a table or index. Enhancements to auto_explain and improved accuracy in pg_stat_statements and pg_stat_activity are also included.
6. Access Control & Security: PostgreSQL 16 enhances the management of pg_hba.conf and pg_ident.conf files, including regular expression matching for user and database names. New security-oriented client connection parameters, support for Kerberos credential delegation, and the use of the trusted CA store provided by the client's OS are added.

These features collectively contribute to better performance, security, and ease of use in PostgreSQL 16.