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<?php
/**
* Version of LockManager based on using DB table locks.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
* http://www.gnu.org/copyleft/gpl.html
*
* @file
* @ingroup LockManager
*/
use Wikimedia\Rdbms\Database;
use Wikimedia\Rdbms\IDatabase;
use Wikimedia\Rdbms\DBError;
/**
* Version of LockManager based on using named/row DB locks.
*
* This is meant for multi-wiki systems that may share files.
*
* All lock requests for a resource, identified by a hash string, will map to one bucket.
* Each bucket maps to one or several peer DBs, each on their own server.
* A majority of peer DBs must agree for a lock to be acquired.
*
* Caching is used to avoid hitting servers that are down.
*
* @ingroup LockManager
* @since 1.19
*/
abstract class DBLockManager extends QuorumLockManager {
/** @var array[]|IDatabase[] Map of (DB names => server config or IDatabase) */
protected $dbServers; // (DB name => server config array)
/** @var BagOStuff */
protected $statusCache;
protected $lockExpiry; // integer number of seconds
protected $safeDelay; // integer number of seconds
/** @var IDatabase[] Map Database connections (DB name => Database) */
protected $conns = [];
/**
* Construct a new instance from configuration.
*
* @param array $config Parameters include:
* - dbServers : Associative array of DB names to server configuration.
* Configuration is an associative array that includes:
* - host : DB server name
* - dbname : DB name
* - type : DB type (mysql,postgres,...)
* - user : DB user
* - password : DB user password
* - tablePrefix : DB table prefix
* - flags : DB flags; bitfield of IDatabase::DBO_* constants
* - dbsByBucket : Array of 1-16 consecutive integer keys, starting from 0,
* each having an odd-numbered list of DB names (peers) as values.
* - lockExpiry : Lock timeout (seconds) for dropped connections. [optional]
* This tells the DB server how long to wait before assuming
* connection failure and releasing all the locks for a session.
* - srvCache : A BagOStuff instance using APC or the like.
*/
public function __construct( array $config ) {
parent::__construct( $config );
$this->dbServers = $config['dbServers'];
// Sanitize srvsByBucket config to prevent PHP errors
$this->srvsByBucket = array_filter( $config['dbsByBucket'], 'is_array' );
$this->srvsByBucket = array_values( $this->srvsByBucket ); // consecutive
if ( isset( $config['lockExpiry'] ) ) {
$this->lockExpiry = $config['lockExpiry'];
} else {
$met = ini_get( 'max_execution_time' );
$this->lockExpiry = $met ? $met : 60; // use some sane amount if 0
}
$this->safeDelay = ( $this->lockExpiry <= 0 )
? 60 // pick a safe-ish number to match DB timeout default
: $this->lockExpiry; // cover worst case
// Tracks peers that couldn't be queried recently to avoid lengthy
// connection timeouts. This is useless if each bucket has one peer.
$this->statusCache = isset( $config['srvCache'] )
? $config['srvCache']
: new HashBagOStuff();
}
/**
* @TODO change this code to work in one batch
* @param string $lockSrv
* @param array $pathsByType
* @return StatusValue
*/
protected function getLocksOnServer( $lockSrv, array $pathsByType ) {
$status = StatusValue::newGood();
foreach ( $pathsByType as $type => $paths ) {
$status->merge( $this->doGetLocksOnServer( $lockSrv, $paths, $type ) );
}
return $status;
}
abstract protected function doGetLocksOnServer( $lockSrv, array $paths, $type );
protected function freeLocksOnServer( $lockSrv, array $pathsByType ) {
return StatusValue::newGood();
}
/**
* @see QuorumLockManager::isServerUp()
* @param string $lockSrv
* @return bool
*/
protected function isServerUp( $lockSrv ) {
if ( !$this->cacheCheckFailures( $lockSrv ) ) {
return false; // recent failure to connect
}
try {
$this->getConnection( $lockSrv );
} catch ( DBError $e ) {
$this->cacheRecordFailure( $lockSrv );
return false; // failed to connect
}
return true;
}
/**
* Get (or reuse) a connection to a lock DB
*
* @param string $lockDb
* @return IDatabase
* @throws DBError
* @throws UnexpectedValueException
*/
protected function getConnection( $lockDb ) {
if ( !isset( $this->conns[$lockDb] ) ) {
if ( $this->dbServers[$lockDb] instanceof IDatabase ) {
// Direct injected connection hande for $lockDB
$db = $this->dbServers[$lockDb];
} elseif ( is_array( $this->dbServers[$lockDb] ) ) {
// Parameters to construct a new database connection
$config = $this->dbServers[$lockDb];
$db = Database::factory( $config['type'], $config );
} else {
throw new UnexpectedValueException( "No server called '$lockDb'." );
}
$db->clearFlag( DBO_TRX );
# If the connection drops, try to avoid letting the DB rollback
# and release the locks before the file operations are finished.
# This won't handle the case of DB server restarts however.
$options = [];
if ( $this->lockExpiry > 0 ) {
$options['connTimeout'] = $this->lockExpiry;
}
$db->setSessionOptions( $options );
$this->initConnection( $lockDb, $db );
$this->conns[$lockDb] = $db;
}
return $this->conns[$lockDb];
}
/**
* Do additional initialization for new lock DB connection
*
* @param string $lockDb
* @param IDatabase $db
* @throws DBError
*/
protected function initConnection( $lockDb, IDatabase $db ) {
}
/**
* Checks if the DB has not recently had connection/query errors.
* This just avoids wasting time on doomed connection attempts.
*
* @param string $lockDb
* @return bool
*/
protected function cacheCheckFailures( $lockDb ) {
return ( $this->safeDelay > 0 )
? !$this->statusCache->get( $this->getMissKey( $lockDb ) )
: true;
}
/**
* Log a lock request failure to the cache
*
* @param string $lockDb
* @return bool Success
*/
protected function cacheRecordFailure( $lockDb ) {
return ( $this->safeDelay > 0 )
? $this->statusCache->set( $this->getMissKey( $lockDb ), 1, $this->safeDelay )
: true;
}
/**
* Get a cache key for recent query misses for a DB
*
* @param string $lockDb
* @return string
*/
protected function getMissKey( $lockDb ) {
return 'dblockmanager:downservers:' . str_replace( ' ', '_', $lockDb );
}
/**
* Make sure remaining locks get cleared for sanity
*/
function __destruct() {
$this->releaseAllLocks();
foreach ( $this->conns as $db ) {
$db->close();
}
}
}
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