The object-relational database management system now known as
PostgreSQL (and briefly called
Postgres95) is derived from the
POSTGRES package written at the University of
California at Berkeley. With over a decade of
development behind it, PostgreSQL
is the most advanced open-source database available anywhere,
offering multiversion concurrency control, supporting almost
all SQL constructs (including subselects, transactions, and
user-defined types and functions), and having a wide range of
language bindings available (including C, C++, Java, Perl, Tcl, and Python).
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. Version 1, described in
The implementation of POSTGRES, was released
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, subsequent
releases until Postgres95 (see below)
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 (later merged into
Informix,
which is now owned by IBM.)
picked up
the code and commercialized it.
POSTGRES became the primary data manager
for the
Sequoia 2000
scientific computing project in late 1992.
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 Berkeley
POSTGRES project officially
ended with Version 4.2.
In 1994, Andrew Yu and Jolly Chen
added a SQL language interpreter to POSTGRES.
Postgres95 was subsequently released to
the Web to find its own way in the world as an
open-source descendant of the original POSTGRES
Berkeley code.
Postgres95 code was completely
ANSI C and trimmed in size by 25%. Many
internal changes improved performance and maintainability.
Postgres95 release 1.0.x ran about 30-50%
faster on the Wisconsin Benchmark compared to
POSTGRES, Version 4.2.
Apart from bug fixes, the following were the major enhancements:
The query language PostQUEL was replaced with
SQL (implemented in the server).
Subqueries were not supported until
PostgreSQL (see below), but they
could be imitated in Postgres95 with user-defined
SQL functions. Aggregates were
re-implemented. Support for the GROUP BY query clause was also added.
The libpq interface remained
available for C
programs.
In addition to the monitor program, a new program
(psql) was provided for interactive SQL queries
using GNUReadline.
A new front-end library, libpgtcl,
supported Tcl-based clients. A sample shell,
pgtclsh, provided new Tcl commands to interface
Tcl
programs with the Postgres95 backend.
The large-object interface was overhauled. The Inversion large objects were
the only mechanism for storing large objects.
(The Inversion file system was removed.)
The instance-level rule system was removed.
Rules were still available as rewrite rules.
A short tutorial introducing regular SQL features as
well as those of Postgres95 was
distributed with the source code
GNU make (instead of BSD make) was used
for the build. Also, Postgres95 could be
compiled with an unpatched GCC
(data alignment of doubles was fixed).
By 1996, it became clear that the name "Postgres95" would
not stand the test of time. We chose a new name,
PostgreSQL, to reflect the relationship
between the original POSTGRES and the more
recent versions with SQL capability. At the same
time, we set the version numbering to start at 6.0, putting the
numbers back into the sequence originally begun by the Berkeley
POSTGRES project.
The emphasis during development of Postgres95
was on identifying and understanding existing problems in the backend code.
With PostgreSQL,
the emphasis has shifted to augmenting features and capabilities, although
work continues in all areas.
Major enhancements in PostgreSQL include:
Table-level locking has been replaced by multiversion concurrency control,
which allows readers to continue reading consistent data during writer activity
and enables hot backups from pg_dump while the database stays available for
queries.
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 coercion,
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 start-up time has decreased by 80% since version 6.0 was released.
