Database administration

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  1. Database Administration for MediaWiki Beginners

This article provides a comprehensive introduction to database administration for users of MediaWiki, specifically tailored for beginners. Understanding these concepts is crucial for maintaining a healthy, performant, and secure wiki. We’ll cover the basics of database systems, common tasks, troubleshooting, and best practices. This guide assumes you are using MySQL/MariaDB, the most common database backend for MediaWiki. While some concepts may apply to other database systems (like PostgreSQL), the specific instructions will focus on MySQL/MariaDB.

What is a Database and Why Does MediaWiki Need One?

At its core, a wiki like MediaWiki stores all its data – pages, revisions, user information, configurations, and more – within a database. Think of a database as a highly organized digital filing system. Instead of storing information in individual text files (which would be incredibly inefficient for a large wiki), a database allows for structured storage, efficient retrieval, and complex relationships between different pieces of data.

MediaWiki *requires* a database to function. Without it, there's no way to persistently store the wiki's content and settings. When you save a page, the content isn’t just written to a file; it’s inserted into the database. When you search for a page, the database is queried to find matching results.

Understanding the Different Database Components

Let's break down the key components of a database system:

  • **Database Server:** This is the software that manages the database. Examples include MySQL, MariaDB, and PostgreSQL. It's responsible for storing, retrieving, and securing the data.
  • **Database:** Within the database server, you create one or more databases. MediaWiki typically uses a single database dedicated solely to its operation.
  • **Tables:** A database is organized into tables. Each table stores data about a specific entity. For example, there's a `page` table, a `user` table, a `revision` table, etc.
  • **Columns:** Each table is comprised of columns. Columns define the types of data stored in that table. For example, the `page` table might have columns for `page_id`, `page_title`, and `page_content`.
  • **Rows:** Each row in a table represents a single record. For example, a row in the `page` table would represent a single wiki page.
  • **Schemas:** The schema defines the structure of the database, including the tables, columns, data types, and relationships between them. MediaWiki comes with a pre-defined schema that you shouldn’t typically modify directly.

Common Database Administration Tasks

As a MediaWiki administrator, you’ll likely encounter several common database administration tasks:

1. **Database Creation:** When you initially set up MediaWiki, you'll need to create a database specifically for it. This is usually done through a tool like phpMyAdmin or the MySQL command line. 2. **User Management:** Creating and managing users with appropriate database privileges is critical for security. You'll need a user that MediaWiki can use to connect to the database. This user should have limited privileges – only the ability to select, insert, update, and delete data within the MediaWiki database. 3. **Backups:** Regularly backing up your database is *essential*. If something goes wrong (hardware failure, data corruption, accidental deletion), a backup is your only way to restore your wiki. See the Backups section below for more details. 4. **Database Optimization:** Over time, a database can become fragmented and slow down. Optimization techniques, such as indexing and analyzing tables, can improve performance. Performance tuning is a key aspect of this. 5. **Database Repair:** If data corruption occurs, you may need to repair the database. MySQL provides tools for this purpose. 6. **Monitoring:** Regularly monitoring database performance and resource usage can help you identify potential problems before they become critical. 7. **Schema Updates:** When you upgrade MediaWiki, the database schema may need to be updated to accommodate new features. MediaWiki provides update scripts for this purpose. 8. **Database Security:** Ensuring the database is secure from unauthorized access is paramount. This includes using strong passwords, limiting user privileges, and keeping the database software up to date.

Backups: Your First Line of Defense

Backups are arguably the most important task of a database administrator. A good backup strategy involves:

  • **Full Backups:** A complete copy of the entire database.
  • **Incremental Backups:** Copies of only the data that has changed since the last full or incremental backup.
  • **Differential Backups:** Copies of only the data that has changed since the last *full* backup.

For MediaWiki, full backups are usually sufficient for smaller wikis. For larger wikis, a combination of full and incremental/differential backups is recommended.

    • Methods for Backing Up:**
  • **`mysqldump`:** A command-line utility that creates a logical backup of the database as a SQL script. This is a common and reliable method. Example: `mysqldump -u [username] -p [database_name] > wiki_backup.sql`
  • **phpMyAdmin:** A web-based interface for managing MySQL databases. It provides a simple way to export the database as a SQL script.
  • **Database Replication:** Creating a replica of your database on a separate server. This provides both a backup and a failover mechanism.
  • **Automated Backup Scripts:** Writing scripts to automate the backup process.
    • Backup Storage:** Store your backups in a secure location *separate* from the web server. Consider using offsite storage (like cloud storage) for added protection. Test your backups regularly to ensure they can be restored successfully. Understanding risk management is vital when planning your backup strategy.

Accessing and Managing Your Database

There are several ways to access and manage your MediaWiki database:

  • **phpMyAdmin:** A popular web-based interface for managing MySQL databases. It provides a graphical user interface for executing SQL queries, browsing tables, and performing other administrative tasks. It's often pre-installed on web hosting servers.
  • **MySQL Command Line:** A powerful and flexible way to interact with the database. Requires knowledge of SQL. Connect using the `mysql` command: `mysql -u [username] -p [database_name]`
  • **MySQL Workbench:** A desktop application that provides a more advanced set of tools for database administration.
  • **Adminer:** A lightweight alternative to phpMyAdmin. It's a single PHP file that can be easily uploaded to your server.

Basic SQL Commands You Should Know

SQL (Structured Query Language) is the standard language for interacting with databases. Here are some basic commands:

  • **`SELECT`:** Retrieves data from a table. Example: `SELECT * FROM page WHERE page_title = 'Main Page';`
  • **`INSERT`:** Inserts new data into a table.
  • **`UPDATE`:** Modifies existing data in a table.
  • **`DELETE`:** Deletes data from a table.
  • **`CREATE TABLE`:** Creates a new table. (Generally not needed for MediaWiki)
  • **`ALTER TABLE`:** Modifies an existing table. (Generally not needed for MediaWiki)
  • **`SHOW TABLES`:** Lists all tables in the database.
  • **`DESCRIBE [table_name]`:** Displays the structure of a table (columns and data types).

Troubleshooting Common Database Issues

  • **“Error Establishing a Database Connection”:** This usually indicates a problem with the database credentials in your `LocalSettings.php` file. Double-check the database hostname, username, password, and database name. Also, ensure the database server is running.
  • **Slow Wiki Performance:** This can be caused by a number of factors, including a large database, inefficient queries, lack of indexing, or insufficient server resources. Use tools like `EXPLAIN` in MySQL to analyze query performance. Review technical analysis tools for identifying bottlenecks.
  • **Database Errors in MediaWiki:** Check the MediaWiki error logs for details. The error message may provide clues about the specific problem.
  • **Data Corruption:** If you suspect data corruption, try running the `CHECK TABLE` command in MySQL. If corruption is detected, use the `REPAIR TABLE` command.
  • **Database Locking:** High traffic or long-running queries can sometimes cause database locking, which can slow down or block access to the wiki. Investigate and optimize long-running queries.

Database Optimization Techniques

  • **Indexing:** Adding indexes to frequently queried columns can significantly improve performance. However, too many indexes can slow down write operations. Consider which columns are most often used in `WHERE` clauses and `JOIN` conditions. Understanding market trends in query usage can help prioritize indexing.
  • **Analyzing Tables:** The `ANALYZE TABLE` command updates the table statistics used by the query optimizer. This helps the optimizer choose the most efficient execution plan.
  • **Optimizing Queries:** Review your SQL queries for inefficiencies. Avoid using `SELECT *` when you only need specific columns. Use appropriate `WHERE` clauses to filter data.
  • **Caching:** MediaWiki has a built-in caching mechanism. Ensure that caching is enabled and configured properly.
  • **Database Server Configuration:** Tune the database server configuration parameters (e.g., buffer pool size, query cache size) to optimize performance for your specific workload. This requires advanced knowledge of MySQL/MariaDB administration. Consider consulting with a database administrator. Analyzing indicators such as query execution time can help refine these settings.

Security Best Practices

  • **Strong Passwords:** Use strong, unique passwords for all database users.
  • **Least Privilege:** Grant users only the privileges they need to perform their tasks. The MediaWiki user should have limited privileges.
  • **Database Firewall:** Configure a firewall to restrict access to the database server.
  • **Regular Updates:** Keep the database software up to date with the latest security patches.
  • **Secure Connections:** Use SSL/TLS to encrypt communication between MediaWiki and the database server.
  • **Input Validation:** Ensure that all user input is properly validated to prevent SQL injection attacks. MediaWiki provides built-in mechanisms for input validation.
  • **Regular Security Audits:** Conduct regular security audits to identify and address potential vulnerabilities. Employing strategies for proactive vulnerability management is key.

Resources for Further Learning

Main Page Configuration Manual:Upgrading Help:Contents Backups Performance tuning Security Extensions Skins Database schema Troubleshooting

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