PostgreSQL is an object-relational database management system (ORDBMS) designed for maximum customization, extensibility and standards-compliance. It provides built-in support for B-tree and hash indexes, as well as support for GiST and GIN, two inverted indexes. Postgres offers advanced support for built-in binary and synchronous replication. It also provides concurrency via an MVCC (Multiversion Concurrency Control) system that gives every transaction a snapshot of the database, so that changes are invisible to other transactions until they are executed. In addition, Postgres natively supports JSON, using a structured format known as JSONB, which enables users to commit documents to the database without having to restructure them. A number of companies and organizations have used Postgres to build applications, websites, and tools, including Genentech, Whitepages.com, University of California, Berkeley, Cisco, and the U.S. State Department.