| Developer(s) | PostgreSQL Global Development Group |
|---|---|
| Stable release | 9.1.2, 9.0.6, 8.4.10, 8.3.17, 8.2.23 / December 5, 2011 |
| Written in | C |
| Operating system | Cross-platform |
| Type | ORDBMS |
| License | PostgreSQL licence[1][2][3] |
| Website | www.postgresql.org |
PostgreSQL, often simply Postgres, is an object-relational database management system (ORDBMS) available for many platforms including Linux, FreeBSD, Solaris, Microsoft Windows and Mac OS X.[4] It is released under the PostgreSQL License, which is an MIT-style license, and is thus free and open source software. PostgreSQL is developed by the PostgreSQL Global Development Group, consisting of a handful of community volunteers employed and supervised by companies such as Red Hat.[5] It implements the majority of the SQL:2008 standard,[6] is ACID-compliant, is fully transactional (including all DDL statements), has extensible data types, operators, and indexes, and has a large number of extensions written by third parties.
The vast majority of Linux distributions have PostgreSQL available in supplied packages. Mac OS X, starting with Lion, has PostgreSQL server as its standard default database in the server edition,[7][8] and PostgreSQL client tools in the desktop edition.
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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 /ˈpoʊstɡrɛs ˌkjuː ˈɛl/; (Audio sample, 5.6k MP3). It is abbreviated as "Postgres", its original name. Because of ubiquitous support for the SQL Standard amongst most 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 use the name PostgreSQL.[9] The name refers to the project's origins as a "post-Ingres" database, being a development from University Ingres DBMS (Ingres being an abbreviation for INteractive Graphics REtrieval System).[10]
PostgreSQL evolved from the Ingres project at the University of California, Berkeley. In 1982, the project leader, Michael Stonebraker, left Berkeley to make a proprietary version of Ingres.[10] 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.[11] 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 of the 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 a MIT-style 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 has been maintained by a group of database developers and volunteers around the world, coordinating via the Internet.
The PostgreSQL project continues to make major releases (approximately annually) and minor "bugfix" releases, all available under the same license. Code comes from contributions from proprietary vendors, support companies, and open-source programmers at large.
| Release | First release | Latest minor version | Latest release | Additions |
|---|---|---|---|---|
| 0.01 | 1995-05-01 | 0.03 | 1995-07-21 | Initial release as Postgres95 |
| 1.0 | 1995-09-05 | 1.09 | 1996-11-04 | Changed copyright to a more liberal license |
| 6.0 | 1997-01-29 | — | Name change from Postgres95 to PostgreSQL, unique indexes, pg_dumpall utility, ident authentication. | |
| 6.1 | 1997-06-08 | 6.1.1 | 1997-07-22 | Multi-column indexes, sequences, money data type, GEQO (GEnetic Query Optimizer). |
| 6.2 | 1997-10-02 | 6.2.1 | 1997-10-17 | JDBC interface, triggers, server programming interface, constraints. |
| 6.3 | 1998-03-01 | 6.3.2 | 1998-04-07 | SQL92 subselect capability, PL/pgTCL |
| 6.4 | 1998-10-30 | 6.4.2 | 1998-12-20 | VIEWs and RULEs, PL/pgSQL |
| 6.5 | 1999-06-09 | 6.5.3 | 1999-10-13 | MVCC, temporary tables, more SQL statement support (CASE, INTERSECT, and EXCEPT) |
| 7.0 | 2000-05-08 | 7.0.3 | 2000-11-11 | Foreign keys, Inner joins |
| 7.1 | 2001-04-13 | 7.1.3 | 2001-08-15 | Write-ahead Log, Outer joins |
| 7.2 | 2002-02-04 | 7.2.8 | 2005-05-09 | PL/Python, OIDs no longer required, internationalization of messages |
| 7.3 | 2002-11-27 | 7.3.21 | 2008-01-07 | Schema, Internationalization |
| 7.4 | 2003-11-17 | 7.4.30 | 2010-10-04 | Optimization all-round |
| 8.0 | 2005-01-19 | 8.0.26 | 2010-10-04 | Native server on Microsoft Windows, savepoints, tablespaces, exception handling in functions, point-in-time recovery |
| 8.1 | 2005-11-08 | 8.1.23 | 2010-12-16 | Performance optimization, two-phase commit, table partitioning, index bitmap scan, shared row locking, roles |
| 8.2 | 2006-12-05 | 8.2.23 | 2011-09-26 | Performance optimization, online index builds, advisory locks, warm standby |
| 8.3 | 2008-02-04 | 8.3.17 | 2011-09-26 | Full text search, SQL/XML, ENUM types, UUID types |
| 8.4 | 2009-07-01 | 8.4.10 | 2011-09-26 | Windowing functions, default and variadic parameters for functions, column-level permissions, parallel database restore, per-database collation, common table expressions and recursive queries |
| 9.0 | 2010-09-20 | 9.0.6 | 2011-09-26 | Built-in binary streaming replication, Hot standby, 64-bit Windows, per-column triggers and conditional trigger execution, exclusion constraints, anonymous code blocks, named parameters, password rules |
| 9.1 | 2011-09-12 | 9.1.2 | 2011-09-26 | Synchronous replication, per-column collations, unlogged tables, K-nearest-neighbor indexing, serializable snapshot isolation, writeable common table expressions, SE-Linux integration, extensions, SQL/MED attached tables, triggers on views |
| Community supported |
| Community support ended[12] |
Procedural languages (often called stored procedures) allow blocks of code to be executed by the database server, and can be written in programming languages other than SQL and C. Procedural languages can be used to create user-defined functions (subroutine, trigger, aggregates and window functions), and can also be used in ad hoc "DO" blocks. The following four procedural languages are provided by a standard PostgreSQL installation:
Other non-standard procedural languages that have been developed outside the core distribution include (but are not limited to):
PostgreSQL includes built-in support for B+-tree, hash, generalized search trees (GiST) and generalized inverted indexes (GIN). In addition, user-defined index methods can be created, although this is quite an involved process. Indexes in PostgreSQL also support the following features:
WHERE clause to the end of the CREATE INDEX statement. This allows a smaller index to be created.Triggers are events triggered by the action of SQL DML statements. For example, an INSERT statement might activate a trigger that checked if the values of the statement were valid. Most triggers are only activated by either INSERT or UPDATE statements.
Triggers are fully supported and can be attached to tables and as of 9.1, this also includes views. Views in versions prior to 9.1 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.
PostgreSQL manages concurrency through a system known as multiversion 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 (atomicity, consistency, isolation, durability) principles in an efficient manner.
Rules allow the "query tree" of an incoming query to be rewritten. One common usage is to implement views, including updatable views. Rules, or more properly, "Query Re-Write Rules", are attached to a table/class and "Re-Write" the incoming DML (select, insert, update, and/or delete) into one or more queries that either replace the original DML statement or execute in addition to it. Query Re-Write occurs after DML statement parsing, but, before query planning.
A wide variety of native data types are supported, including:
In addition, users can create their own data types which can usually be made fully indexable via PostgreSQL's GiST infrastructure. Examples of these include the geographic information system (GIS) data types from the PostGIS project for PostgreSQL.
There is also a data type called a "domain", which is the same as any other data type but with optional constraints defined by the creator of that domain. This means any data entered into a column using the domain will have to conform to whichever constraints were defined as part of the domain.
New types of almost all objects inside the database can be created, including:
Tables can be set to inherit their characteristics from a "parent" table. Data in child tables will appear to exist in the parent tables, unless data is selected from the parent table using the ONLY keyword, i.e. select * from ONLY PARENT_TABLE. Adding a column in the parent table will cause that column to appear in the child table.
Inheritance can be used to implement table partitioning, using either triggers or rules to direct inserts to the parent table into the proper child tables.
As of 2010[update] this feature is not fully supported yet—in particular, table constraints are not currently inheritable. As of the 8.4 release, all check constraints and not-null constraints on a parent table are automatically inherited by its children. Other types of constraints (unique, primary key, and foreign key constraints) are not inherited.
Inheritance provides a way to map the features of generalization hierarchies depicted in Entity Relationship Diagrams (ERD) directly into the PostgreSQL database.
PostgreSQL comes with additional extensions, libraries and tools that are referred to as contrib modules.
Extensions aren't installed in databases by default, but they can be installed on a per-database basis to provide additional functionality and features. In PostgreSQL 9.1 and later, these can be installed via the CREATE EXTENSION command. Older versions execute an SQL script in the database they are to be installed in.
Libraries add system-wide functionality rather than per database. These can be loaded into individual sessions, or configured to be preloaded into the server to be made automatically available to all sessions.
Tools are applications used outside of the database and provide various utility functions.
| Extension | Description | Type | Available from version |
|---|---|---|---|
| adminpack | Provides a number of support functions which pgAdmin and other administration and management tools can use to provide additional functionality, such as remote management of server log files. | Extension | 8.2 |
| auth_delay | Causes the server to pause briefly before reporting authentication failure, to make brute-force attacks on database passwords more difficult. | Library | 9.1 |
| autoexplain | Automatic logging of the plans of slow-running queries. | Library | 8.4 |
| btree_gin | Provides GIN operator classes that implement B-Tree equivalent behavior for various data types. | Extension | 8.4 |
| btree_gist | Provides GiST operator classes that implement B-Tree equivalent behavior for various data types. | Extension | 8.0 |
| chkpass | Implements a data type chkpass that is designed for storing encrypted passwords. | Extension | 8.3 |
| citext | Provides a case-insensitive character string type, citext. | Extension | 8.4 |
| cube | Implements a data type cube for representing multi-dimensional cubes. | Extension | 8.3 |
| dblink | Adds support for connections to other PostgreSQL databases from within a database session. | Extension | 7.4 |
| dict_int | Adds an example add-on dictionary template for full-text search to control the indexing of integers (signed and unsigned), allowing such numbers to be indexed while preventing excessive growth in the number of unique words, which greatly affects the performance of searching. | Extension | 8.3 |
| dict_xsyn | Adds an example add-on dictionary template for full-text search which replaces words with groups of their synonyms, and so makes it possible to search for a word using any of its synonyms. | Extension | 8.3 |
| dummy_seclabel | A library to support regression testing of the SECURITY LABEL statement. It is not intended to be used in production. | Library | 9.1 |
| earthdistance | Provides two different approaches to calculating great circle distances on the surface of the Earth. | Extension | 8.3 |
| file_fdw | Provides the foreign-data wrapper file_fdw, which can be used to access data files in the server's file system and query them as tables. | Extension | 9.1 |
| fuzzystrmatch | Provides several functions to determine similarities and distance between strings consisting of Soundex, Levenshtein, Metaphone and Double Metaphone. | Extension | 7.4 |
| hstore | Implements the hstore data type for storing sets of key/value pairs within a single PostgreSQL value. | Extension | 8.2 |
| intarray | Provides a number of useful functions and operators for manipulating null-free arrays of integers. There is also support for indexed searches using some of the operators. | Extension | 7.4 |
| isn | Provides data types for the following international product numbering standards: EAN13, UPC, ISBN (books), ISMN (music), and ISSN (serials). | Extension | 8.2 |
| lo | Provides support for managing Large Objects (also called LOs or BLOBs). It includes a data type lo and a trigger lo_manage. | Extension | 8.3 |
| ltree | Implements a data type ltree for representing labels of data stored in a hierarchical tree-like structure. Extensive facilities for searching through label trees are provided. | Extension | 7.4 |
| oid2name | A utility program that helps administrators to examine the file structure used by PostgreSQL. | Tool | 8.3 |
| pageinspect | Provides functions that allow you to inspect the contents of database pages at a low level, which is useful for debugging purposes. | Extension | 8.3 |
| passwordcheck | Checks users' passwords whenever they are defined for database roles. This utilises CrackLib to enforce password strength rules. | Library | 9.0 |
| pg_archivecleanup | A application designed to be used as an archive_cleanup_command to clean up WAL file archives when running as a standby server. It can also be used as a standalone program to clean WAL file archives. | Tool | 9.0 |
| pg_buffercache | Provides a means for examining what's happening in the shared buffer cache in real time. | Extension | 8.1 |
| pg_freespacemap | Provides a means for examining the free space map. | Extension | 8.2 |
| pg_standby | An application to support the creation of a "warm standby" database server. | Tool | 8.3 |
| pg_stat_statements | Provides a means for tracking execution statistics of all SQL statements executed by a server. | Extension | 8.4 |
| pg_test_fsync | An application to check the fastest sync method of Write Ahead Log files on the system, and provide diagnostic information. | Tool | 9.1 |
| pg_trgm | Provides functions and operators for determining the similarity of ASCII alphanumeric text based on trigram matching, as well as index operator classes that support fast searching for similar strings. | Extension | 8.0 |
| pg_upgrade | An application which allows data stored in PostgreSQL data files to be upgraded to a later PostgreSQL major version without the data dump/reload typically required for major version upgrades. | Tool | 8.4 |
| pgbench | A benchmarking application to perform various types of performance test against PostgreSQL. | Tool | 7.4 |
| pgcrypto | Provides various cryptographic functions | Extension | 8.3 |
| pgrowlocks | Provides a function to show row locking information for a specified table. | Extension | 8.3 |
| pgstattuple | Provides various functions to obtain tuple-level statistics. | Extension | 7.4 |
| seg | Implements a data type seg for representing line segments, or floating point intervals. seg can represent uncertainty in the interval endpoints, making it especially useful for representing laboratory measurements. | Extension | 7.4 |
| sepgsql | A loadable module which supports label-based mandatory access control (MAC) based on SELinux security policy. | Library | 9.1 |
| spi | Provides several workable examples of using SPI and triggers. | Extension | 8.3 |
| sslinfo | Provides information about the SSL certificate that the current client provided when connecting to PostgreSQL. | Extension | 8.2 |
| tablefunc | Includes various functions that return tables (that is, multiple rows) including ones to produce crosstab (pivot) queries. | Extension | 7.4 |
| unaccent | A text search dictionary that removes accents (diacritic signs) from lexemes. It's a filtering dictionary, which means its output is always passed to the next dictionary (if any), unlike the normal behavior of dictionaries. This allows accent-insensitive processing for full text search. | Extension | 9.0 |
| uuid-ossp | Provides functions to generate universally unique identifiers (UUIDs) using one of several standard algorithms. There are also functions to produce certain special UUID constants. | Extension | 8.3 |
| vacuumlo | A simple utility program that will remove any "orphaned" large objects from a PostgreSQL database. | Tool | 8.3 |
There are many other extensions available outside of core distribution. PGXN (PostgreSQL Extension Network) is one source of extensions, but many others are available from sources such as GitHub and SourceForge.
PostgreSQL, beginning from version 9.0, includes built-in binary replication, based on shipping the changes (write-ahead logs) to slave systems asynchronously.
Beginning from version 9.1, PostgreSQL also includes built-in synchronous replication[16] that ensures that, for each write transaction, the master waits until at least one slave node has written the data to its transaction log.
Version 9.0 also introduced the ability to run read-only queries against these replicated slaves, where earlier versions would only allow that after promoting them to be a new master. This allows splitting read traffic among multiple nodes efficiently. Earlier replication software that allowed similar read scaling normally relied on adding replication triggers to the master, introducing additional load onto it.
There are also several asynchronous trigger-based replication packages for PostgreSQL. These remain useful even after introduction of the expanded core capabilities, for situations where binary replication of an entire database cluster isn't the appropriate approach:
Proxy (middleware) tools enable replication, failover or load management and balancing for PostgreSQL:
The following features are due to appear in the 9.2 release of PostgreSQL:
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.
The pgAdmin package is a free and open source graphical user interface administration tool for PostgreSQL, which is supported on many computer platforms.[26] The program is available in more than a dozen languages. The first prototype, named pgManager, was written for PostgreSQL 6.3.2 from 1998, and rewritten and released as pgAdmin under the GPL License in later months. The second incarnation (named pgAdmin II) was a complete rewrite, first released on January 16, 2002. The third version, pgAdmin III, was originally released under the Artistic License and then released under the same license as PostgreSQL. Unlike prior versions that were written in Visual Basic, pgAdmin III is written in C++, using the wxWidgets framework allowing it to run on most common operating systems.
phpPgAdmin is a web-based administration tool for PostgreSQL written in PHP and based on the popular phpMyAdmin interface originally written for MySQL administration.[27]
OpenOffice.org Base can be used as a front-end for PostgreSQL.[28]
The pgFouine PostgreSQL log analyzer generates detailed reports from a PostgreSQL log file and provides VACUUM analysis.[29]
A number of companies offer proprietary tools for PostgreSQL. They often consist of a universal core that is adapted for various specific database products. These tools mostly share the administration features with the open source tools but offer improvements in data modeling, importing, exporting or reporting.
Many informal performance studies of PostgreSQL have been done.[30] Performance improvements aimed at improving scalability started heavily with version 8.1, and running simple benchmarks version 8.4 has been shown to be more than 10 times faster on read only workloads and at least 7.5 times faster on both read and write workloads compared with version 8.0.[31]
The first industry-standard and peer-validated benchmark was completed in June 2007 using the Sun Java System Application Server (proprietary version of GlassFish) 9.0 Platform Edition, UltraSPARC T1 based Sun Fire server and Postgres 8.2.[32] This result of 778.14 SPECjAppServer2004 JOPS@Standard compares favourably with the 874 JOPS@Standard with Oracle 10 on an Itanium based HP-UX system.[30]
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.[33]
The default configuration of PostgreSQL only uses a small amount of dedicated memory for performance-critical purposes such as caching database blocks and sorting. This limitation is primarily because older operating systems required kernel changes to allow allocating large blocks of shared memory.[34] PostgreSQL.org provides advice on basic recommended performance practice in a wiki.[35]
As of 2008[update] PostgreSQL has received the following awards:[52]
Although the license allowed proprietary products based on Postgres, the code did not develop in the proprietary space at first. The main offshoot originated when Paula Hawthorn (an original Ingres team member who moved from Ingres) and Michael Stonebraker formed Illustra Information Technologies to make a proprietary product based on Postgres.
In 2000, former Red Hat investors created the company Great Bridge to make a proprietary product based on PostgreSQL and compete against proprietary database vendors. Great Bridge sponsored several PostgreSQL developers and donated many resources back to the community,[53] but by late 2001 closed due to tough competition from companies like Red Hat and to poor market conditions.[54]
In 2001, Command Prompt, Inc. released Mammoth PostgreSQL, a proprietary product based on PostgreSQL. In 2008, Command Prompt, Inc. released the source under the original license. Command Prompt, Inc. continues to support the PostgreSQL community actively 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. In July 2006, Pervasive left the PostgreSQL support market.[55]
In mid-2005 two other companies announced plans to make proprietary products based on 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 are looking at PostgreSQL right now,"[56] although no specifics were released at that time. By November 2005, Sun had announced support for PostgreSQL.[57] By June 2006, Sun Solaris 10 (6/06 release) shipped with PostgreSQL.
In August 2007, EnterpriseDB announced[58] the Postgres Resource Center and EnterpriseDB Postgres, designed as a fully configured distribution of PostgreSQL including many contrib modules and add-on components. EnterpriseDB Postgres was renamed to Postgres Plus in March 2008. Postgres Plus is available in two versions: Postgres Plus Standard Server which has all the features of PostgreSQL plus additional QA testing, integrated components, tuning and one-click install, and Postgres Plus Advanced Server which has all the features of Postgres Plus Standard Server plus Oracle compatibility, scalability features, and DBA and developer tools. Both versions are available for free and are fully supported, though the free version of Postgres Plus Advanced Server is restricted by a "limited use" license, which is defined as "confined to a single CPU, utilizing 1 GB RAM, storing no more than 6 GB of data in a NON-PRODUCTION environment."