Major enhancements in PostgreSQL 9.4 include:
Add jsonb, a more capable and efficient data type for storing JSON data
Add new SQL command ALTER SYSTEM for changing postgresql.conf configuration
file entries
Reduce lock strength for some ALTER TABLE commands
Allow materialized views to be refreshed without blocking concurrent reads
Add support for logical decoding of WAL data, to allow database changes to be
streamed out in a customizable format
Allow background worker processes to be dynamically registered, started and
terminated The above items are explained in more detail in the sections below.
URL: http://www.postgresql.org/docs/9.4/static/release-9-4.html
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