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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
*/
/**
* 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, all having the filelocks.sql tables (with row-level locking).
* 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 Map of DB names to server config */
protected $dbServers; // (DB name => server config array)
/** @var BagOStuff */
protected $statusCache;
protected $lockExpiry; // integer number of seconds
protected $safeDelay; // integer number of seconds
protected $session = 0; // random integer
/** @var Array Map Database connections (DB name => Database) */
protected $conns = array();
/**
* Construct a new instance from configuration.
*
* $config paramaters 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 (see DatabaseBase)
* - dbsByBucket : Array of 1-16 consecutive integer keys, starting from 0,
* each having an odd-numbered list of DB names (peers) as values.
* Any DB named 'localDBMaster' will automatically use the DB master
* settings for this wiki (without the need for a dbServers entry).
* Only use 'localDBMaster' if the domain is a valid wiki ID.
* - 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.
*
* @param array $config
*/
public function __construct( array $config ) {
parent::__construct( $config );
$this->dbServers = isset( $config['dbServers'] )
? $config['dbServers']
: array(); // likely just using 'localDBMaster'
// 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
foreach ( $this->srvsByBucket as $bucket ) {
if ( count( $bucket ) > 1 ) { // multiple peers
// Tracks peers that couldn't be queried recently to avoid lengthy
// connection timeouts. This is useless if each bucket has one peer.
try {
$this->statusCache = ObjectCache::newAccelerator( array() );
} catch ( MWException $e ) {
trigger_error( __CLASS__ .
" using multiple DB peers without apc, xcache, or wincache." );
}
break;
}
}
$this->session = wfRandomString( 31 );
}
/**
* @see QuorumLockManager::isServerUp()
* @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 $lockDb string
* @return DatabaseBase
* @throws DBError
*/
protected function getConnection( $lockDb ) {
if ( !isset( $this->conns[$lockDb] ) ) {
$db = null;
if ( $lockDb === 'localDBMaster' ) {
$lb = wfGetLBFactory()->getMainLB( $this->domain );
$db = $lb->getConnection( DB_MASTER, array(), $this->domain );
} elseif ( isset( $this->dbServers[$lockDb] ) ) {
$config = $this->dbServers[$lockDb];
$db = DatabaseBase::factory( $config['type'], $config );
}
if ( !$db ) {
return null; // config error?
}
$this->conns[$lockDb] = $db;
$this->conns[$lockDb]->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 = array();
if ( $this->lockExpiry > 0 ) {
$options['connTimeout'] = $this->lockExpiry;
}
$this->conns[$lockDb]->setSessionOptions( $options );
$this->initConnection( $lockDb, $this->conns[$lockDb] );
}
if ( !$this->conns[$lockDb]->trxLevel() ) {
$this->conns[$lockDb]->begin( __METHOD__ ); // start transaction
}
return $this->conns[$lockDb];
}
/**
* Do additional initialization for new lock DB connection
*
* @param $lockDb string
* @param $db DatabaseBase
* @return void
* @throws DBError
*/
protected function initConnection( $lockDb, DatabaseBase $db ) {}
/**
* Checks if the DB has not recently had connection/query errors.
* This just avoids wasting time on doomed connection attempts.
*
* @param $lockDb string
* @return bool
*/
protected function cacheCheckFailures( $lockDb ) {
return ( $this->statusCache && $this->safeDelay > 0 )
? !$this->statusCache->get( $this->getMissKey( $lockDb ) )
: true;
}
/**
* Log a lock request failure to the cache
*
* @param $lockDb string
* @return bool Success
*/
protected function cacheRecordFailure( $lockDb ) {
return ( $this->statusCache && $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 $lockDb string
* @return string
*/
protected function getMissKey( $lockDb ) {
$lockDb = ( $lockDb === 'localDBMaster' ) ? wfWikiID() : $lockDb; // non-relative
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();
}
}
}
/**
* MySQL version of DBLockManager that supports shared locks.
* All locks are non-blocking, which avoids deadlocks.
*
* @ingroup LockManager
*/
class MySqlLockManager extends DBLockManager {
/** @var Array Mapping of lock types to the type actually used */
protected $lockTypeMap = array(
self::LOCK_SH => self::LOCK_SH,
self::LOCK_UW => self::LOCK_SH,
self::LOCK_EX => self::LOCK_EX
);
/**
* @param $lockDb string
* @param $db DatabaseBase
*/
protected function initConnection( $lockDb, DatabaseBase $db ) {
# Let this transaction see lock rows from other transactions
$db->query( "SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;" );
}
/**
* Get a connection to a lock DB and acquire locks on $paths.
* This does not use GET_LOCK() per http://bugs.mysql.com/bug.php?id=1118.
*
* @see DBLockManager::getLocksOnServer()
* @return Status
*/
protected function getLocksOnServer( $lockSrv, array $paths, $type ) {
$status = Status::newGood();
$db = $this->getConnection( $lockSrv ); // checked in isServerUp()
$keys = array(); // list of hash keys for the paths
$data = array(); // list of rows to insert
$checkEXKeys = array(); // list of hash keys that this has no EX lock on
# Build up values for INSERT clause
foreach ( $paths as $path ) {
$key = $this->sha1Base36Absolute( $path );
$keys[] = $key;
$data[] = array( 'fls_key' => $key, 'fls_session' => $this->session );
if ( !isset( $this->locksHeld[$path][self::LOCK_EX] ) ) {
$checkEXKeys[] = $key;
}
}
# Block new writers (both EX and SH locks leave entries here)...
$db->insert( 'filelocks_shared', $data, __METHOD__, array( 'IGNORE' ) );
# Actually do the locking queries...
if ( $type == self::LOCK_SH ) { // reader locks
$blocked = false;
# Bail if there are any existing writers...
if ( count( $checkEXKeys ) ) {
$blocked = $db->selectField( 'filelocks_exclusive', '1',
array( 'fle_key' => $checkEXKeys ),
__METHOD__
);
}
# Other prospective writers that haven't yet updated filelocks_exclusive
# will recheck filelocks_shared after doing so and bail due to this entry.
} else { // writer locks
$encSession = $db->addQuotes( $this->session );
# Bail if there are any existing writers...
# This may detect readers, but the safe check for them is below.
# Note: if two writers come at the same time, both bail :)
$blocked = $db->selectField( 'filelocks_shared', '1',
array( 'fls_key' => $keys, "fls_session != $encSession" ),
__METHOD__
);
if ( !$blocked ) {
# Build up values for INSERT clause
$data = array();
foreach ( $keys as $key ) {
$data[] = array( 'fle_key' => $key );
}
# Block new readers/writers...
$db->insert( 'filelocks_exclusive', $data, __METHOD__ );
# Bail if there are any existing readers...
$blocked = $db->selectField( 'filelocks_shared', '1',
array( 'fls_key' => $keys, "fls_session != $encSession" ),
__METHOD__
);
}
}
if ( $blocked ) {
foreach ( $paths as $path ) {
$status->fatal( 'lockmanager-fail-acquirelock', $path );
}
}
return $status;
}
/**
* @see QuorumLockManager::freeLocksOnServer()
* @return Status
*/
protected function freeLocksOnServer( $lockSrv, array $paths, $type ) {
return Status::newGood(); // not supported
}
/**
* @see QuorumLockManager::releaseAllLocks()
* @return Status
*/
protected function releaseAllLocks() {
$status = Status::newGood();
foreach ( $this->conns as $lockDb => $db ) {
if ( $db->trxLevel() ) { // in transaction
try {
$db->rollback( __METHOD__ ); // finish transaction and kill any rows
} catch ( DBError $e ) {
$status->fatal( 'lockmanager-fail-db-release', $lockDb );
}
}
}
return $status;
}
}
/**
* PostgreSQL version of DBLockManager that supports shared locks.
* All locks are non-blocking, which avoids deadlocks.
*
* @ingroup LockManager
*/
class PostgreSqlLockManager extends DBLockManager {
/** @var Array Mapping of lock types to the type actually used */
protected $lockTypeMap = array(
self::LOCK_SH => self::LOCK_SH,
self::LOCK_UW => self::LOCK_SH,
self::LOCK_EX => self::LOCK_EX
);
protected function getLocksOnServer( $lockSrv, array $paths, $type ) {
$status = Status::newGood();
if ( !count( $paths ) ) {
return $status; // nothing to lock
}
$db = $this->getConnection( $lockSrv ); // checked in isServerUp()
$bigints = array_unique( array_map(
function( $key ) { return wfBaseConvert( substr( $key, 0, 15 ), 16, 10 ); },
array_map( array( $this, 'sha1Base16Absolute' ), $paths )
) );
// Try to acquire all the locks...
$fields = array();
foreach ( $bigints as $bigint ) {
$fields[] = ( $type == self::LOCK_SH )
? "pg_try_advisory_lock_shared({$db->addQuotes( $bigint )}) AS K$bigint"
: "pg_try_advisory_lock({$db->addQuotes( $bigint )}) AS K$bigint";
}
$res = $db->query( 'SELECT ' . implode( ', ', $fields ), __METHOD__ );
$row = (array)$res->fetchObject();
if ( in_array( 'f', $row ) ) {
// Release any acquired locks if some could not be acquired...
$fields = array();
foreach ( $row as $kbigint => $ok ) {
if ( $ok === 't' ) { // locked
$bigint = substr( $kbigint, 1 ); // strip off the "K"
$fields[] = ( $type == self::LOCK_SH )
? "pg_advisory_unlock_shared({$db->addQuotes( $bigint )})"
: "pg_advisory_unlock({$db->addQuotes( $bigint )})";
}
}
if ( count( $fields ) ) {
$db->query( 'SELECT ' . implode( ', ', $fields ), __METHOD__ );
}
foreach ( $paths as $path ) {
$status->fatal( 'lockmanager-fail-acquirelock', $path );
}
}
return $status;
}
/**
* @see QuorumLockManager::freeLocksOnServer()
* @return Status
*/
protected function freeLocksOnServer( $lockSrv, array $paths, $type ) {
return Status::newGood(); // not supported
}
/**
* @see QuorumLockManager::releaseAllLocks()
* @return Status
*/
protected function releaseAllLocks() {
$status = Status::newGood();
foreach ( $this->conns as $lockDb => $db ) {
try {
$db->query( "SELECT pg_advisory_unlock_all()", __METHOD__ );
} catch ( DBError $e ) {
$status->fatal( 'lockmanager-fail-db-release', $lockDb );
}
}
return $status;
}
}