手册:数据库访问

This page is a translated version of the page Manual:Database access and the translation is 61% complete.

本文概述了MediaWiki中的数据库访问和常规数据库问题。

在MediaWiki中进行编码时,通常只能为此目的通过MediaWiki的功能访问数据库。

数据库设计

有关MediaWiki数据库设计的信息,例如表及其内容的描述,请参见手册:数据库布局 和$tables。 Historically in MediaWiki, this was also documented in maintenance/tables.sql, however, starting in MediaWiki 1.35, this is being gradually moved into maintenance/tables.json as part of the Abstract Schema initiative. This means the maintenance/tables.json is turned into maintenance/tables-generated.sql by a maintenance script , making it easier to generate schema files to support different database engines.

登录至MySQL

使用sql.php

MediaWiki提供了一个维护脚本来访问数据库。从maintenance目录运行:

php sql.php

然后,您可以写出数据库查询。或者,您可以提供一个文件名,然后MediaWiki将执行该文件,并酌情替换任何MW特殊变量。 有关更多信息,请参见手册:Sql.php

这将适用于所有数据库后端。但是,提示功能没有数据库附带的命令行客户端的那样丰富。

使用mysql命令行客户端

## 数据库设置
$wgDBtype           = "mysql";
$wgDBserver         = "localhost";
$wgDBname           = "your-database-name";
$wgDBuser           = "your-database-username";  // Default: root
$wgDBpassword       = "your-password";

在LocalSettings.php中,您将找到维基的MySQL密码和用户名,例如:

使用SSH,请输入以下内容进行登录:

mysql -u <$wgDBuser> -p --database=<$wgDBname>

LocalSettings.php信息替换<$wgDBuser><$wgDBname>。然后将提示您输入密码$wgDBpassword,此后您将看到mysql>提示符。

数据库抽象层

MediaWiki提供了一个数据库抽象层。除非您在抽象层上工作,否则永远不要直接调用PHP的数据库函数(例如mysql_query()或者pg_send_query())。

可通过Wikimedia\Rdbms\Database类访问抽象层。 可以通过在注入的ILoadBalancer上调用getConnectionRef()(首选)或getConnection()来获取此类的实例。 函数wfGetDB()正在逐步淘汰,不应在新代码中使用。 通常使用以下两个参数之一调用,可以是DB_REPLICA(用于读取查询)或DB_PRIMARY(用于写入查询和需要具有绝对最新信息的读取查询)常量。在多数据库环境,例如Wikimedia中,母版和副本之间的区别很重要。请参阅下面的包装函数部分,以了解如何使用返回的Database对象。

选择查询结果的包装是数组,其键是从1开始的整数。要进行读取查询,通常需要满足以下条件:

$lb = MediaWikiServices::getInstance()->getDBLoadBalancer();
...
$dbr = $lb->getConnectionRef( DB_REPLICA );
$res = $dbr->select( /* ...see docs... */ );
foreach( $res as $row ) {
	...
}

对于write查询,请使用类似以下内容的内容:

$dbw = $lb->getConnectionRef( DB_PRIMARY );
$dbw->insert( /* ...see docs... */ );

我们约定使用$dbr进行读取,使用$dbw进行写入,以帮助您注意数据库对象是副本对象(只读)还是主对象(读/写)。 如果您向副本写入,就会遇到问题。 确切地说,在主服务器上成功执行的后续写请求,由于唯一的键冲突,复制到副本时可能会失败。 副本上的复制将停止,可能需要数小时才能修复数据库并使它恢复联机状态。 在副本服务器上的my.cnf中设置read_only可以避免这种情况,但是考虑到可怕的后果,我们希望有尽可能多的代码检查。

包装函数

我们为纯SQL提供了query()函数,但是select()和insert()之类的包装函数通常更方便。 在某些情况下,它们可以处理诸如表前缀和转义之类的事情。 如果您确实需要编写自己的SQL,请阅读tableName()和addQuotes()的文档。您将需要他们两个。请记住,不正确使用addQuotes()可能会给您的Wiki带来严重的安全漏洞。

使用高级方法而不是构造自己的查询的另一个重要原因是要确保无论数据库类型如何,代码都能正确运行。 当前,支持最好的是MySQL/MariaDB。SQLite也有很好的支持,但是它比MySQL或MariaDB慢得多。有对PostgreSQL的支持,但不如MySQL稳定。

在下面,列出了可用的包装函数。 有关包装函数的参数的详细说明,请参阅Database类的文档。 特别注意查看Database::select中关于$table$vars$conds$fname$options$join_conds的说明,这些参数被许多其他包装函数使用。

The parameters $table, $vars, $conds, $fname, $options, and $join_conds should NOT be null or false (that was working until REL 1.35) but empty string '' or empty array [].
function select( $table, $vars, $conds = '', $fname = 'Database::select', $options = [], $join_conds = [] );
function selectField( $table, $var, $cond = '', $fname = __METHOD__, $options = [] );
function selectRow( $table, $vars, $conds = '', $fname = 'Database::select', $options = [] );
function insert( $table, $a, $fname = 'Database::insert', $options = [] );
function insertSelect( $destTable, $srcTable, $varMap, $conds, $fname = 'Database::insertSelect', $insertOptions = [], $selectOptions = [] );
function update( $table, $values, $conds, $fname = 'Database::update', $options = [] );
function delete( $table, $conds, $fname = 'Database::delete' );
function deleteJoin( $delTable, $joinTable, $delVar, $joinVar, $conds, $fname = 'Database::deleteJoin' );
function buildLike(/*...*/);

包装函数: select()

select()函数为SELECT语句提供MediaWiki接口。 SELECT语句的组件被编写为select()函数的参数。 一个例子是:

$dbr = $lb->getConnectionRef( DB_REPLICA );
$res = $dbr->select(
	'category',                              // $table The table to query FROM (or array of tables)
	[ 'cat_title', 'cat_pages' ],            // $vars (columns of the table to SELECT)
	'cat_pages > 0',                         // $conds (The WHERE conditions)
	__METHOD__,                              // $fname The current __METHOD__ (for performance tracking)
	[ 'ORDER BY' => 'cat_title ASC' ]        // $options = []
);

这个例子对应于查询

SELECT cat_title, cat_pages FROM category WHERE cat_pages > 0 ORDER BY cat_title ASC

也可以使用JOIN;例如:

$res = $dbw->select(
	[ 'watchlist', 'user_properties' ],
	[ 'wl_user' ],
	[
		'wl_user != 1' ,
		'wl_namespace' => '0',
		'wl_title' => 'Main_page',
		'up_property' => 'enotifwatchlistpages',
	],
	__METHOD__,
	[],
	[
		'user_properties' => [ 'INNER JOIN', [ 'wl_user=up_user' ] ]
	]
);

这个例子对应于查询

SELECT wl_user FROM `watchlist` INNER JOIN `user_properties` ON ((wl_user=up_user)) WHERE (wl_user != 1) AND wl_namespace = '0' AND wl_title = 'Main_page'
AND up_property = 'enotifwatchlistpages'

Extension:OrphanedTalkPages 提供了在请求中使用表别名一个例子

Arguments are either single values (such as 'category' and 'cat_pages > 0') or arrays, if more than one value is passed for an argument position (such as ['cat_pages > 0', $myNextCond]). If you pass in strings to the third or fifth argument, you must manually use Database::addQuotes() on your values as you construct the string, as the wrapper will not do this for you. The values for table names (1st argument) or field names (2nd argument) must not be user controlled. The array construction for $conds is somewhat limited; it can only do equality and IS NULL relationships (i.e. WHERE key = 'value').

You can access individual rows of the result using a foreach loop. Once you have a row object, you can use the -> operator to access a specific field. 完整的示例可能是:

$dbr = $lb->getConnectionRef( DB_REPLICA );
$res = $dbr->select(
	'category',                              // $table
	[ 'cat_title', 'cat_pages' ],            // $vars (columns of the table)
	'cat_pages > 0',                         // $conds
	__METHOD__,                              // $fname = 'Database::select',
	[ 'ORDER BY' => 'cat_title ASC' ]        // $options = []
);        
$output = '';
foreach( $res as $row ) {
        $output .= 'Category ' . $row->cat_title . ' contains ' . $row->cat_pages . " entries.\n";
}

Which will put an alphabetical list of categories with how many entries each category has in the variable $output. If you are outputting as HTML, ensure to escape values from the database with htmlspecialchars()

Convenience functions

MediaWiki版本:
1.30

For compatibility with PostgreSQL, insert ids are obtained using nextSequenceValue() and insertId(). The parameter for nextSequenceValue() can be obtained from the CREATE SEQUENCE statement in maintenance/postgres/tables.sql and always follows the format of x_y_seq, with x being the table name (e.g. page) and y being the primary key (e.g. page_id), e.g. page_page_id_seq. For example:

$id = $dbw->nextSequenceValue( 'page_page_id_seq' );
$dbw->insert( 'page', [ 'page_id' => $id ] );
$id = $dbw->insertId();

For some other useful functions, e.g. affectedRows(), numRows(), etc., see Manual:Database.php.

基本查询优化

需要编写数据库查询的MediaWiki开发人员应该对数据库以及与之相关的性能问题有所了解。 包含令人无法接受的缓慢功能的补丁将不被接受。 除了从QueryPage派生的特殊页面之外,MediaWiki通常不欢迎未索引的查询。 对于新开发人员来说,提交包含检索大量行的SQL查询的代码是一个常见的陷阱。 请记住,COUNT(*)的复杂度是O(N)的,对表中的行进行计数就像对水桶中的豆子进行计数一样。

Backward compatibility

Often, due to design changes to the DB, different DB accesses are necessary to ensure backward compatibility. This can be handled for example with the global variables $wgDBprefix and $wgVersion :

$res = WrapperClass::getQueryFoo();

class WrapperClass {

	public static function getQueryFoo() {
		global $wgDBprefix, $wgVersion;

		$param = '';
		if ( version_compare( $wgVersion, '1.33', '<' ) ) {
			$param = self::getQueryInfoFooBefore_v1_33( $wgDBprefix );
		} else {
			$param = self::getQueryInfoFoo( $wgDBprefix );
		}

		return = $dbw->select(
			$param['tables'],
			$param['fields'],
			$param['conds'],
			__METHOD__,
			$param['options'],
			$param['join_conds'] );
	}

	private static function getQueryInfoFoo( $prefix ) {
		return [
			'tables' => [ 'table1', 'table2', 'table3' ],
			'fields' => [
				'field_name1' => $prefix . 'table1.field1',
				'field_name2' => 'field2',
				
			],
			'conds' => [ 
			],
			'join_conds' => [
				'table2' => [
					'INNER JOIN',
					
				],
				'table3' => [
					'LEFT JOIN',
					
				]
			],
			'options' => [ 
			]
		];
	}

	private static function getQueryInfoFooBefore_v1_33( $prefix ) {
		return [
			'tables' => [ 'table1', 'table2', 'table3_before' ],
			'fields' => [
				'field_name1' => $prefix . 'table1.field1',
				'field_name2' => 'field2_before',
				
			],
			'conds' => [ 
			],
			'join_conds' => [
				'table2' => [
					'INNER JOIN',
					
				],
				'table3_before' => [
					'LEFT JOIN',
					
				]
			],
			'options' => [ 
			]
		];
	}
}

副本

诸如Wikipedia之类使用MediaWiki的大型网站,使用大量的MySQL副本服务器来复制对主MySQL服务器的写入。 It is important to understand the issues associated with this setup if you want to write code destined for Wikipedia.

通常情况下,用于给定任务的最佳算法取决于是否使用副本。 Due to our unabashed Wikipedia-centrism, we often just use the replication-friendly version, but if you like, you can use wfGetLB()->getServerCount() > 1 to check to see if replication is in use.

滞后

滞后主要发生在将大的写查询发送到主服务器时。 在主服务器上的写操作是并行执行的,但是将它们复制到副本时,它们是串行执行的。 提交任务后,主服务器将查询写入二进制日志。 副本服务器轮询二进制日志并在查询出现后立即开始执行查询。 他们可以在执行写查询时为读取提供服务,但不会再从二进制日志中读取任何内容,因此将不再执行任何写操作。 这意味着,如果写查询运行了很长时间,则副本将在完成写查询所需的时间上落后于主服务器。

高读取负载会加剧延迟。 当副本滞后30秒以上时,MediaWiki的负载平衡器将停止向副本发送读取请求。 如果负载比率设置不正确,或者通常负载太大,则可能导致副本永久滞后30秒左右。

如果所有副本的滞后时间都超过30秒(根据$wgDBservers ),MediaWiki将停止写入数据库。 将拒绝所有编辑和其他写入操作,并向用户返回错误。 这给了副本一个赶上的机会。 在使用这种机制之前,副本通常会滞后几分钟,从而使查看最近的编辑变得困难。

除此之外,MediaWiki尝试确保用户按时间顺序查看Wiki上发生的事件。 只要用户从后续请求中看到一致的画面,就可以容忍几秒钟的延迟。 This is done by saving the primary binlog position in the session, and then at the start of each request, waiting for the replica to catch up to that position before doing any reads from it. If this wait times out, reads are allowed anyway, but the request is considered to be in "lagged replica mode". Lagged replica mode can be checked by calling wfGetLB()->getLaggedReplicaMode(). The only practical consequence at present is a warning displayed in the page footer.

Shell users can check replication lag with getLagTimes.php ; the other users with the siteinfo API.

Databases often have their own monitoring systems in place as well, see for instance wikitech:MariaDB#Replication lag (Wikimedia) and wikitech:Help:Toolforge/Database#Identifying lag (Wikimedia Cloud VPS).

避免滞后

为了避免过多的滞后,应该拆分写入大量行的查询,通常一次只写一行。 多行 INSERT ... SELECT 查询是最严重的问题,应完全避免。 Instead do the select first and then the insert.

Even small writes can cause lag if they are done at a very high speed and replication is unable to keep up. This most commonly happens in maintenance scripts. To prevent it, you should call LBFactory::waitForReplication() after every few hundred writes. Most scripts make the exact number configurable:

class MyMaintenanceScript extends Maintenance {
    public function __construct() {
        // ...
        $this->setBatchSize( 100 );
    }

    public function execute() {
        $lbFactory = MediaWikiServices::getInstance()->getDBLoadBalancerFactory();
        $limit = $this->getBatchSize();
        while ( true ) {
             // ...select up to $limit rows to write, break the loop if there are no more rows...
             // ...do the writes...
             $lbFactory->waitForReplication();
        }
    }
}

Working with lag

Despite our best efforts, it's not practical to guarantee a low-lag environment. Replication lag will usually be less than one second, but may occasionally be up to 30 seconds. For scalability, it's very important to keep load on the primary server low, so simply sending all your queries to the primary server is not the answer. So when you have a genuine need for up-to-date data, the following approach is advised:

  1. Do a quick query to the primary server for a sequence number or timestamp
  2. Run the full query on the replica and check if it matches the data you got from the primary server
  3. If it doesn't, run the full query on the primary server

To avoid swamping the primary server every time the replicas lag, use of this approach should be kept to a minimum. In most cases you should just read from the replica and let the user deal with the delay.

Lock contention

由于Wikipedia(和其他一些Wiki)上的写入率很高,MediaWiki开发人员需要非常小心地构造其写入内容,以避免长时间的锁定。 默认情况下,MediaWiki在第一个查询中打开一个任务,并在发送输出之前将其提交。 从查询完成到提交为止,将保持锁定状态。 因此,在执行写查询之前,可以通过尽可能多的处理来减少锁定时间。 通过将对象添加到$wgPostCommitUpdateList ,可以将不需要数据库访问的更新操作延迟到提交之后。

Often this approach is not good enough, and it becomes necessary to enclose small groups of queries in their own transaction. 使用以下语法:

$factory = \MediaWiki\MediaWikiServices::getInstance()->getDBLoadBalancerFactory();
$factory->beginMasterChanges(__METHOD__);
/* Do queries */
$factory->commitMasterChanges(__METHOD__);

Use of locking reads (e.g. the FOR UPDATE clause) is not advised. They are poorly implemented in InnoDB and will cause regular deadlock errors. It's also surprisingly easy to cripple the wiki with lock contention.

Instead of locking reads, combine your existence checks into your write queries, by using an appropriate condition in the WHERE clause of an UPDATE, or by using unique indexes in combination with INSERT IGNORE. Then use the affected row count to see if the query succeeded.

数据库架构

Don't forget about indexes when designing databases, things may work smoothly on your test wiki with a dozen of pages, but will bring a real wiki to a halt. 有关详细信息,请参见上方

For naming conventions, see Manual:Coding conventions/Database .

SQLite兼容性

When writing MySQL table definitions or upgrade patches, it is important to remember that SQLite shares MySQL's schema, but that works only if definitions are written in a specific way:

  • Primary keys must be declared within main table declaration, but normal keys should be added separately with CREATE INDEX:
CREATE TABLE /*_*/foo (
    foo_id INT NOT NULL AUTO_INCREMENT,
    foo_text VARCHAR(256),
    PRIMARY KEY(foo_id),
    KEY(foo_text)
);
CREATE TABLE /*_*/foo (
    foo_id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
    foo_text VARCHAR(256)
) /*$wgDBTableOptions*/;

CREATE INDEX /*i*/foo_text ON /*_*/foo (foo_text);

However, primary keys spanning over more than one field should be included in the main table definition:

CREATE TABLE /*_*/foo (
    foo_id INT NOT NULL,
    foo_text VARCHAR(256),
    PRIMARY KEY(foo_id, foo_text)
) /*$wgDBTableOptions*/;

CREATE INDEX /*i*/foo_text ON /*_*/foo (foo_text);
/*i*/ has been removed in MediaWiki 1.35, see Variable replacement.
  • Don't add more than one column per statement:
ALTER TABLE /*_*/foo
    ADD foo_bar BLOB,
    ADD foo_baz INT;
ALTER TABLE /*_*/foo ADD foo_bar BLOB;
ALTER TABLE /*_*/foo ADD foo_baz INT;
  • Set explicit defaults when adding NOT NULL columns:
ALTER TABLE /*_*/foo ADD COLUMN foo_bar varchar(32) BINARY NOT NULL;
ALTER TABLE /*_*/foo ADD COLUMN foo_bar varchar(32) BINARY NOT NULL DEFAULT '';

您可以使用以下方法运行基本兼容性检查:

或者,如果您需要测试补丁更新,请执行以下两项操作:

  • php sqlite.php --check-syntax tables.sql (使用新的“tables.sql”)
  • php sqlite.php --check-syntax tables.sql filename.sql
    • Since DB patches update the tables.sql file as well, for this one you should pass in the pre-commit version of tables.sql (the file with the full DB definition). Otherwise, you can get an error if you e.g. drop an index (since it already doesn't exist in tables.sql because you just removed it).

The above assumes you're in $IP/maintenance/, otherwise, pass the full path of the file. For extension patches, use the extension's equivalent of these files.

参见