WHAT IS MYSQL?

MySQL (pronounced (IPA) /m?? ?s kju? ?l/, "my S-Q-L"[1]) is a multithreaded, multi-user SQL database management system (DBMS)[2] which has, according to MySQL AB, more than 10 million installations.[3] The basic program runs as a server providing multiuser access to a number of databases.

MySQL is owned and sponsored by a single for-profit firm, the Swedish company MySQL AB, which holds the copyright to most of the codebase. This is similar to the JBoss model. It is dissimilar to the Apache project, where the software is developed by a public community and the copyright to the codebase is owned by its individual authors. Some industry observers believe MySQL will file for an IPO in early 2008.[citation needed]

The company develops and maintains the system, selling support and service contracts, as well as proprietary-licensed copies of MySQL, and employing people all over the world who collaborate via the Internet. MySQL AB was founded by David Axmark, Allan Larsson, and Michael "Monty" Widenius. The CEO is Mårten Mickos.

The MySQL company used to sell another DBMS, MaxDB, which is from an unrelated codebase. MaxDB's sales and support have reverted back to SAP AG, where it originated[4].
Contents

History

* MySQL was first released internally on May 23, 1995
* Windows version released on January 8, 1998 for Windows 95 and NT
* Version 3.23: beta from June 2000, production release January 2001
* Version 4.0: beta from August 2002, production release March 2003 (unions)
* Version 4.1: beta from June 2004, production release October 2004 (r-trees, subqueries, prepared statements)
* Version 5.0: beta from March 2005, production release October 2005 (cursors, stored procedures, triggers, views, XA transactions)
* Version 5.1: currently pre-production (since November 2005) (event scheduler, partitioning, plugin API, row-based replication, server log tables)

Programming languages

Libraries for accessing MySQL databases are available in all major programming languages with language-specific APIs. In addition, an ODBC interface called MyODBC allows additional programming languages that support the ODBC interface to communicate with a MySQL database, such as ASP or ColdFusion. The MySQL server and official libraries are mostly implemented in ANSI C/ANSI C++.

Uses

MySQL is popular for web applications and acts as the database component of the LAMP, MAMP, and WAMP platforms (Linux/Mac/Windows-Apache-MySQL-PHP/Perl/Python), and for open-source bug tracking tools like Bugzilla. Its popularity for use with web applications is closely tied to the popularity of PHP and Ruby on Rails, which is often combined with MySQL. PHP and MySQL are essential components for running popular content management systems such as Joomla!, WordPress and Drupal. Wikipedia runs on MediaWiki software, which is written in PHP and uses a MySQL database.

Documentation and administration

Information on using MySQL can be found on the company's site, under their Documentation section. There are also many books written about MySQL.

To administer MySQL databases one can use the included command-line tool (commands: mysql and mysqladmin). Also downloadable from the MySQL site are GUI administration tools: MySQL Administrator and MySQL Query Browser. Both of the GUI tools are now included in one package called MySQL GUI Tools.

In addition to the above mentioned tools developed by MySQL AB, there are several other commercial and non-commercial tools available. phpMyAdmin is a free software webbased administration interface implemented in PHP.

Program specifications

Platforms

MySQL works on many different platforms — including AIX, BSDi, FreeBSD, HP-UX, i5/OS, GNU/Linux, Mac OS X, NetBSD, Novell NetWare, OpenBSD, OS/2 Warp, QNX, SGI IRIX, Solaris, SunOS, SCO OpenServer, SCO UnixWare, Tru64, Windows 95, Windows 98, Windows ME, Windows NT, Windows 2000, Windows XP and Windows Vista. A port of MySQL to OpenVMS is also available.[5]

The latest production version

As of August 2007, MySQL offers MySQL 5.0 in two different variants: the MySQL Community Server and Enterprise Server. Both have a common code base and include the following features:

* A broad subset of ANSI SQL 99, as well as extensions
* Cross-platform support
* Stored procedures
* Triggers
* Cursors
* Updatable Views
* True VARCHAR support
* INFORMATION_SCHEMA
* Strict mode
* X/Open XA distributed transaction processing (DTP) support; two phase commit as part of this, using Oracle's InnoDB engine
* Independent storage engines (MyISAM for read speed, InnoDB for transactions and referential integrity, Archive for storing historical data in little space)
* Transactions with the InnoDB, BDB and Cluster storage engines; savepoints with InnoDB
* SSL support
* Query caching
* Sub-SELECTs (i.e. nested SELECTs)
* Replication with one master per slave, many slaves per master, no automatic support for multiple masters per slave.
* Full-text indexing and searching using MyISAM engine
* Embedded database library
* Partial Unicode support (UTF-8 sequences longer than 3 bytes are not supported; UCS-2 encoded strings are also limited to the BMP)
* ACID compliance using the InnoDB, BDB and Cluster engines
* Shared-nothing clustering through MySQL Cluster

The MySQL Enterprise Server is released once per month and the sources can be obtained either from MySQL's customer-only Enterprise site or from MySQL's BitKeeper repository, both under the GPL license. The MySQL Community Server is published on an unspecified schedule under the GPL and contains all bug fixes that were shipped with the last MySQL Enterprise Server release. Binaries are no longer provided by MySQL for every release of the Community Server.[6][7]

Future releases

The MySQL 5.1 roadmap outlines support for:

* Pluggable storage engine API
* Partitioning
* Event Scheduling
* XML functions
* Row-based replication[8]

Support for parallelization is also part of the roadmap for future versions.[9]

Foreign key support for all storage engines will likely be released with MySQL 5.2 (although it has been present since version 3.23.44 for InnoDB).

The current MySQL 5.1 development release is 5.1.22 RC.

A new storage engine is also in the works, called Falcon. A preview of Falcon is already available on Apache's website.

Distinguishing features

The following features are implemented by MySQL but not by some other RDBMSes:

* Multiple storage engines, allowing you to choose the one which is most effective for each table in the application (in MySQL 5.0, storage engines must be compiled in; in MySQL 5.1, storage engines can be dynamically loaded at run time):
* Native storage engines (MyISAM, Falcon, Merge, Memory (heap), Federated, Archive, CSV, Blackhole, Cluster, BDB, EXAMPLE)
* Partner-developed storage engines (InnoDB, solidDB, NitroEDB, BrightHouse)
* Community-developed storage engines (memcached, httpd, PBXT)
* Custom storage engines
* Commit grouping, gathering multiple transactions from multiple connections together to increase the number of commits per second.

Server compilation type

There are 3 types of MySQL Server Compilations for Enterprise and Community users:

* Standard: The MySQL-Standard binaries are recommended for most users, and include the InnoDB storage engine.
* Max: (not MaxDB, which is a cooperation with SAP AG) is mysqld-max Extended MySQL Server. The MySQL-Max binaries include additional features that may not have been as extensively tested or are not required for general usage.
* The MySQL-Debug binaries have been compiled with extra debug information, and are not intended for production use, because the included debugging code may cause reduced performance.

Beginning with MySQL 5.1, MySQL AB has stopped providing these different package variants. There will only be one MySQL server package, which includes a mysqld binary with all functionality and storage engines enabled. Instead of providing a separate debug package, a server binary with extended debugging information is also included in the standard package.[10]

Source code specifics

MySQL is written in C and C++. The SQL parser uses yacc and home-brewed lexer. A document describing some of the internal structures of the code and the coding guidelines is available from the MySQL web site.[11]

Support

Via MySQL Enterprise MySQL AB offers support itself, including 24/7 30-minute response time, with the support team having direct access to the developers as necessary to handle problems. In addition it hosts forums and mailing lists and employees and other users are often available in several IRC channels providing assistance.

Buyers of MySQL Enterprise enjoy access to binaries and software that is certified for their particular operating system, and access to monthly binary updates with the latest bug fixes. Several levels of Enterprise membership are available, with varying response times and features ranging from how to and emergency support through server performance tuning and system architecture advice. The MySQL Network Monitoring and Advisory Service monitoring tool for database servers is available only to MySQL Enterprise customers.

Licensing

MySQL AB makes MySQL Server available as free software under the GNU General Public License (GPL), but they also offer the MySQL Enterprise subscription offering for business users and dual-license it under traditional proprietary licensing arrangements for cases where the intended use is incompatible with the GPL.

Both the MySQL server software itself and the client libraries are distributed under a dual-licensing format. Users may choose the GNU General Public License[12], which MySQL has extended with a FLOSS License Exception. It allows Software licensed under other OSI-compliant Open Source licenses, which are not compatible to the GPL, to link against the MySQL client libraries.[13]

Customers that do not wish to be bound to the terms of the GPL may choose to purchase a proprietary license.[14]

Like many open-source programs, the name "MySQL" is trademarked and may only be used with the trademark holder's permission.

Some users have independently continued to develop earlier versions of the client libraries, which was distributed under the less-restrictive Lesser General Public License.[15]

Issues

There has been some controversy regarding the distribution of GPLed MySQL library files with other open source applications. The biggest controversy arose with PHP, which has a license incompatible with the GPL. This was later resolved when MySQL created a license exception that explicitly allows the inclusion of the MySQL client library in open source projects that are licensed under a number of OSI-compliant Open Source licenses, including the PHP License.[16]

In September 2005, MySQL AB and SCO forged a partnership for "joint certification, marketing, sales, training and business development work for a commercial version of the database for SCO's new OpenServer 6 version of Unix". SCO raised controversy beginning in 2003 with a number of high-profile patent lawsuits related to the Linux Operating System. Various MySQL employees expressed that the company was committed to serving its end users, regardless of their operating system choice, that the company would leave it to the courts to resolve the SCO licensing controversy, and that other common open source databases have also been ported to, and support, SCO OpenServer.

In October 2005, Oracle Corporation acquired Innobase OY, the Finnish company that developed the InnoDB storage engine that allows MySQL to provide such functionality as transactions and foreign keys. A press release[17] by Oracle that was issued after the acquisition mentioned that the contracts that make the company's software available to MySQL AB come up for renewal (and presumably renegotiation) some time in 2006. During the MySQL Users Conference in April 2006, MySQL issued a press release which confirmed that MySQL and Innobase OY agreed to a multi-year extension of their licensing agreement.[18]

In February 2006, Oracle Corporation acquired Sleepycat Software,[19] makers of the Berkeley DB, a database engine onto which another MySQL storage engine was built.

Criticism

Early versions of MySQL lacked many standard relational database management system (RDBMS) features, usually with the goal of trading guaranteed accuracy for speed. Many (but not yet all) such criticisms have been remedied in later versions of the software, including transactions and relational integrity constraints — features necessary to support "ACID properties" for relational databases, which allow the DBMS to ensure that client applications cannot interfere with one another or insert inconsistent values.[20]

Earlier versions of the MySQL manual included claims that certain missing ACID features were useless or even harmful, and that users were better off without them. One section, entitled "Reasons NOT to use Foreign Keys constraints" (sic), advised users that relational-integrity checking was difficult to use and complicated a database application, and that its only useful purpose was to allow client software to diagram the relationships between database tables.[21] Another section claimed that a DBMS lacking transactions can provide data-integrity assurances as reliable as those provided by a DBMS that supports transactions — thus conflating the issue of transactional integrity with that of saving data when the database server loses power.[22]

Another criticism is MySQL's divergence from the SQL standard on the subject of treatment of NULL values and default values. Its handling of dates allows storing a date with a day beyond the last day of a month with fewer than 31 days, and arithmetic operations are vulnerable to either integer overflow or floating point truncation.[23] Since version 5 of the server, the treatment of illegal values varies according to use of the "SQL Mode" set in the server, which is by default set to the unusually tolerant state that critics dislike.[24]

When the beta version of MySQL 5.0 was released in March 2005, David Axmark, a co-founder of MySQL, said that "People have been criticizing MySQL since we started for not having stored procedures, triggers and views," and "We're fixing 10 years of criticism in one release."[25] MySQL 5.0's 13 October build 5.0.15 was released for production use on 24 October 2005, after more than two million downloads in the 5.0 beta cycle.

MySQL Application of the Year winners

2007

* YouTube
* Amp'd Mobile
* Adobe

2006

* Nokia, using MySQL Cluster to maintain real-time information about mobile network users.
* flickr, Using MySQL to manage millions of photos and users.[26]
* NetQOS, embeds MySQL to manage the world's largest networks including Chevron, American Express and Boeing.

2005

* CNET Networks
* Friendster, in 2005 more than 85 million dynamic page views per day, able to support more than 1.5 billion MySQL queries per day
* Wikipedia, in early 2005 more than 200 million queries and 1.2 million updates per day with peak loads of 11,000 queries per second