Implementation of the Postgres DBMS began in 1986. The initial concepts for the system were presented in The Design of Postgres and the definition of the initial data model appeared in The Postgres Data Model. The design of the rule system at that time was described in The Design of the Postgres Rules System. The rationale and architecture of the storage manager were detailed in The Postgres Storage System.
Postgres has undergone several major releases since then. The first "demoware" system became operational in 1987 and was shown at the 1988 ACM-SIGMOD Conference. We released Version 1, described in The Implementation of Postgres, to a few external users in June 1989. In response to a critique of the first rule system (A Commentary on the Postgres Rules System), the rule system was redesigned (On Rules, Procedures, Caching and Views in Database Systems) and Version 2 was released in June 1990 with the new rule system. Version 3 appeared in 1991 and added support for multiple storage managers, an improved query executor, and a rewritten rewrite rule system. For the most part, releases since then have focused on portability and reliability.
Postgres has been used to implement many different research and production applications. These include: a financial data analysis system, a jet engine performance monitoring package, an asteroid tracking database, a medical information database, and several geographic information systems. Postgres has also been used as an educational tool at several universities. Finally, Illustra Information Technologies (since merged into Informix) picked up the code and commercialized it. Postgres became the primary data manager for the Sequoia 2000 scientific computing project in late 1992. Furthermore, the size of the external user community nearly doubled during 1993. It became increasingly obvious that maintenance of the prototype code and support was taking up large amounts of time that should have been devoted to database research. In an effort to reduce this support burden, the project officially ended with Version 4.2.
In 1994, Andrew Yu and Jolly Chen added a SQL language interpreter to Postgres, and the code was subsequently released to the Web to find its own way in the world. Postgres95 was a public-domain, open source descendant of this original Berkeley code.
Postgres95 is a derivative of the last official release of Postgres (version 4.2). The code is now completely ANSI C and the code size has been trimmed by 25%. There are a lot of internal changes that improve performance and code maintainability. Postgres95 v1.0.x runs about 30-50% faster on the Wisconsin Benchmark compared to v4.2. Apart from bug fixes, these are the major enhancements:
The query language Postquel has been replaced with SQL (implemented in the server). We do not yet support subqueries (which can be imitated with user defined SQL functions). Aggregates have been re-implemented. We also added support for ``GROUP BY''. The libpq interface is still available for C programs.
In addition to the monitor program, we provide a new program (psql) which supports GNU readline.
We added a new front-end library, libpgtcl, that supports Tcl-based clients. A sample shell, pgtclsh, provides new Tcl commands to interface tcl programs with the Postgres95 backend.
The large object interface has been overhauled. We kept Inversion large objects as the only mechanism for storing large objects. (This is not to be confused with the Inversion file system which has been removed.)
The instance-level rule system has been removed. Rules are still available as rewrite rules.
A short tutorial introducing regular SQL features as well as those of ours is distributed with the source code.
GNU make (instead of BSD make) is used for the build. Also, Postgres95 can be compiled with an unpatched gcc (data alignment of doubles has been fixed).
By 1996, it became clear that the name “Postgres95” would not stand the test of time. A new name, PostgreSQL, was chosen to reflect the relationship between original Postgres and the more recent versions with SQL capability. At the same time, the version numbering was reset to start at 6.0, putting the numbers back into the sequence originally begun by the Postgres Project.
The emphasis on development for the v1.0.x releases of Postgres95 was on stabilizing the backend code. With the v6.x series of PostgreSQL, the emphasis has shifted from identifying and understanding existing problems in the backend to augmenting features and capabilities, although work continues in all areas.
Major enhancements include:
Important backend features, including subselects, defaults, constraints, and triggers, have been implemented.
Additional SQL92-compliant language features have been added, including primary keys, quoted identifiers, literal string type coersion, type casting, and binary and hexadecimal integer input.
Built-in types have been improved, including new wide-range date/time types and additional geometric type support.
Overall backend code speed has been increased by approximately 20-40%, and backend startup time has decreased 80% since v6.0 was released.