Everything about Postgresql totally explained
| latest_preview_version =
| latest_preview_date =
| operating_system =
Cross-platform
| programming_language =
C
| genre =
ORDBMS
| license =
BSD license
| website = http://www.postgresql.org/
}}
PostgreSQL is an
object-relational database management system (ORDBMS). It is released under a
BSD-style license and is thus
free software. As with many other open-source programs, PostgreSQL isn't controlled by any single company, but relies on a global community of developers and companies to develop it.
Product name
The mixed-capitalization of the PostgreSQL name can confuse some people on first viewing. The several pronunciations of '
SQL' can lead to this confusion. PostgreSQL's developers pronounce it /poːst ɡɹɛs kjuː ɛl/; (
Audio sample
, 5.6k
MP3). It is also common to hear it abbreviated as simply "postgres", which was its original name. Because of ubiquitous support for the amongst all relational databases, the community considered changing the name back to Postgres. However, the PostgreSQL Core Team announced in 2007 that the product would continue to be named PostgreSQL. The name refers to the project's origins as a "post-Ingres" database, the original authors having also developed the
Ingres database.
History
PostgreSQL evolved from the
Ingres project at
University of California, Berkeley. In 1982, the project leader,
Michael Stonebraker, left Berkeley to commercialize Ingres. He returned to Berkeley in 1985 and started a post-Ingres project to address the problems with contemporary database systems that had become increasingly clear during the early 1980s. The new project, Postgres, aimed to add the fewest features needed to completely support types. These features included the ability to define types and to fully describe relationships – something used widely before but maintained entirely by the user. In Postgres, the database "understood" relationships, and could retrieve information in related tables in a natural way using
rules. Postgres used many ideas of Ingres but not its code.
Starting in 1986, the team published a number of papers describing the basis of the system, and by 1988 had a prototype version. The team released version 1 to a small number of users in June 1989, then version 2 with a re-written rules system in June 1990. Version 3, released in 1991, again re-wrote the rules system, and added support for multiple storage managers and an improved query engine. By 1993 the great number of users began to overwhelm the project with requests for support and features. After releasing version 4 — primarily a cleanup — the project ended.
But
open-source developers could obtain copies and develop the system further, because Berkeley had released Postgres under the
BSD license. In 1994, Berkeley graduate students Andrew Yu and Jolly Chen replaced the Ingres-based
QUEL query language interpreter with one for the
SQL query language, creating Postgres95. The code was released on the web.
In July 1996, Marc Fournier at Hub.Org Networking Services provided the first non-university development server for the open source development effort. Along with Bruce Momjian and Vadim B. Mikheev, work began to stabilize the code inherited from Berkeley. The first open source version was released on August 1, 1996.
In 1996, the project was renamed to PostgreSQL to reflect its support for SQL. The first PostgreSQL release formed version 6.0 in January 1997. Since then, the software was maintained by a group of database developers and volunteers around the world, coordinating via the
Internet.
Although the license allowed for the commercialization of Postgres, the code didn't develop commercially at first — somewhat surprisingly considering the advantages Postgres offered. The main offshoot originated when Paula Hawthorn (an original Ingres team member who moved from Ingres) and Michael Stonebraker formed
Illustra Information Technologies to commercialize Postgres.
In 2000, former
Red Hat investors created the company Great Bridge to commercialize PostgreSQL and compete against commercial database vendors. Great Bridge sponsored several PostgreSQL developers and donated many resources back to the community, but by late 2001 closed due to tough competition from companies like Red Hat and to poor market conditions.
In 2001, Command Prompt, Inc. released Mammoth PostgreSQL, the oldest surviving commercial PostgreSQL distribution. It continues to actively support the PostgreSQL community through developer sponsorships and projects including PL/Perl, PL/php, and hosting of community projects such as the
PostgreSQL Build Farm.
In January 2005, PostgreSQL received backing by database vendor
Pervasive Software, known for its
Btrieve product which was ubiquitous on the
Novell NetWare platform. Pervasive announced commercial support and community participation and achieved some success. But in July 2006, it left the PostgreSQL support market.
In mid-2005 two other companies announced plans to commercialize PostgreSQL with focus on separate niche markets.
EnterpriseDB added functionality to allow applications written to work with
Oracle to be more readily run with PostgreSQL.
Greenplum contributed enhancements directed at
data warehouse and
business intelligence applications, including the BizGres project.
In October 2005, John Loiacono,
executive vice president of software at
Sun Microsystems, commented: "We're not going to
OEM Microsoft but we're looking at PostgreSQL right now," although no specifics were released at that time. By November 2005, Sun had announced support for PostgreSQL.
As of June 2006, Sun Solaris 10 6/06 ships PostgreSQL.
In August, 2007, EnterpriseDB announced the Postgres Resource Center
(External Link) and EnterpriseDB Postgres, designed to be a fully configured distribution of PostgreSQL including many contrib modules and add-on components.
The PostgreSQL project continues to make yearly major releases and minor "bugfix" releases, all available under the BSD license, based on contributions from both commercial vendors, support companies, and open source programmers at large.
Features
Functions
Functions allow blocks of code to be executed by the server. Although these blocks can be written in SQL, the lack of basic programming operations, such as
branching and
looping, has driven the adoption of other languages inside of functions. Some of the languages can even execute inside of triggers. Functions in PostgreSQL can be written in the following languages:
PostgreSQL supports row-returning functions, where the output of the function is a set of values which can be treated much like a table within queries.
Functions can be defined to execute with the privileges of either the caller or the user who defined the function. Functions are sometimes referred to as
stored procedures, although there's a slight technical distinction between the two.
Indices
User-defined
index methods can be created, or the built-in
B-tree,
hash table and
GiST indices can be used. Indexes in PostgreSQL also support the following features:
PostgreSQL is capable of scanning indexes backwards when needed; a separate index is never needed to support ORDER BY field DESC.
Expression indexes can be created with an index of the result of an expression or function, instead of simply the value of a column.
Partial indexes, which only index part of a table, can be created by adding a WHERE clause to the end of the CREATE INDEX statement. This allows a smaller index to be created.
Triggers
Triggers are events triggered by the action of SQL query. For example, an INSERT query might activate a trigger that checked if the values of the query were valid. Most triggers are only activated by either INSERT or UPDATE queries.
Triggers are fully supported and can be attached to tables but not to views. Views can have rules, though. Multiple triggers are fired in alphabetical order. In addition to calling functions written in the native PL/PgSQL, triggers can also invoke functions written in other languages like PL/Perl.
MVCC
PostgreSQL manages concurrency through a system known as Multi-Version Concurrency Control (MVCC), which gives each user a "snapshot" of the database, allowing changes to be made without being visible to other users until a transaction is committed. This largely eliminates the need for read locks, and ensures the database maintains the ACID principles in an efficient manner.
Rules
Rules allow the "query tree" of an incoming query to be rewritten. One common usage is to implement updatable views.
Data types
A wide variety of native data types are supported, including:
Arbitrary precision numerics
Unlimited length text
Geometric primitives
IPv4 and IPv6 addresses
CIDR blocks, and MAC address data types
Arrays
XML (as of 8.3)
In addition, users can create their own data types which can usually be made fully indexable via PostgreSQL's GiST infrastructure.
Examples of these are the Geographic information system (GIS) data types from the PostGIS project for PostgreSQL.
User-defined objects
New types of almost all objects inside the database can be created, including:
Indices
Operators (existing ones can be overloaded)
Aggregate functions
Domains
Casts
Conversions
Inheritance
Tables can be set to inherit their characteristics from a "parent" table. Data is shared between "parent" and "child(ren)" tables. Tuples inserted or deleted in the "child" table will respectively be inserted or deleted in the "parent" table. Also adding a column in the parent table will cause that column to appear in the child table as well. This feature isn't fully supported yet—in particular, table constraints are not currently inheritable. This means that attempting to insert the id of a row from a child table into a table that has a foreign key constraint referencing a parent table will fail because Postgres doesn't recognize that the id from the child table is also a valid id in the parent table.
Inheritance provides a way to map the features of generalization hierarchies depicted in Entity Relationship Diagrams (ERD) directly into the PostgreSQL database.
Other features
Referential integrity constraints including foreign key constraints, column constraints, and row checks
Views While updateable views have not been implemented, the same functionality can be achieved using the rules system.
Full, inner, and outer (left and right) joins
Sub-selects
Transactions
Supports most of the major features of standard (External Link) unsupported supported <-- lead to documentation for the next release of PostgreSQL, follow this link to find manuals for already released versions of PostgreSQL
Encrypted connections via SSL
Binary and textual large-object storage
Online backup
Domains
Tablespaces
Savepoints
Point-in-time recovery
Two-phase commit
TOAST (The Oversized-Attribute Storage Technique) is used to transparently store large table attributes (such as big MIME attachments or XML messages) in a separate area, with automatic compression.
Regular expressions (External Link)
Add-ons
Geographic objects via PostGIS. GPL.
Shortest-Path-Algorithms with pgRouting using PostGIS. GPL.
Full text search via Tsearch2 and OpenFTS. (As of 8.3, Tsearch2 included in core PostgreSQL)
Some synchronous multi-master derivatives or extensions exist, including
Several asynchronous master/slave replication packages, including
Database administration front-ends
psql
The primary front-end for PostgreSQL is the psql command-line program, which can be used to enter SQL queries directly, or execute them from a file. In addition, psql provides a number of meta-commands and various shell-like features to facilitate writing scripts and automating a wide variety of tasks; for example tab completion of object names and SQL syntax.
pgAdmin
pgAdmin is a graphical front-end administration tool for PostgreSQL, which is supported on most popular computer platforms. The program is available in more than a dozen languages, and is free software released under the Artistic License. The first prototype, named pgManager, was written for PostgreSQL 6.3.2 from 1998. The stable release (named pgAdmin II) was first released on 16 January 2002. The current version is pgAdmin III, which is released under the Artistic License.
phpPgAdmin
phpPgAdmin is a web-based administration tool for PostgreSQL written in PHP and based on the popular phpMyAdmin interface originally written for MySQL administration.
Benchmarks
Many informal performance studies of PostgreSQL have been done but the first industry-standard and peer-validated benchmark was completed in June 2007 using the Sun Java Systems Application Server 9.0 Platform Edition, UltraSPARC T1 based Sun Fire server and Postgres 8.2. This result of 778.14 SPECjAppServer2004 JOPS@Standard compares favourably with the 874 JOPS@Standard with Oracle 10 on an Itanium based HP-UX
In August 2007, Sun submitted an improved benchmark score of 813.73 SPECjAppServer2004 JOPS@Standard. With the system under test at a reduced price, the price/performance improved from $US 84.98/JOPS to $US 70.57/JOPS.
Prominent users
Yahoo! for web user behavioral analysis, storing 2 petabytes and claimed to be the largest data warehouse using a modified version of PostgreSQL.
Afilias, domain registries for .org, .info and others.
Sony Online multiplayer online games.
BASF, shopping platform for their agribusiness portal.
hi5.com social networking portal.
Skype VoIP application, central business databases.
Sun xVM, Sun's virtualization and datacenter automation suite
Evergreen, an open source integrated library system providing Online Public Access Catalog for many public library systems
Awards
As of 2008 PostgreSQL has received the following awards:
1999 LinuxWorld Editor's Choice Award for Best Database
2000 Linux Journal Editors' Choice Awards for Best Database
2002 Linux New Media Editors Choice Award for Best Database
2003 Linux Journal Editors' Choice Awards for Best Database
2004 Linux New Media Award For Best Database
2004 Linux Journal Editors' Choice Awards for Best Database
2004 ArsTechnica Best Server Application Award
2005 Linux Journal Editors' Choice Awards for Best Database
2006 Linux Journal Editors' Choice Awards for Best Database
2008 Developer.com Product of the Year, Database ToolFurther Information
Get more info on 'Postgresql'.
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