Current File : /www/varak.net/wiki.varak.net/includes/libs/rdbms/chronologyprotector/ChronologyProtector.php
<?php
/**
* Generator of database load balancing objects.
*
* 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 Database
*/
use Psr\Log\LoggerAwareInterface;
use Psr\Log\LoggerInterface;
/**
* Class for ensuring a consistent ordering of events as seen by the user, despite replication.
* Kind of like Hawking's [[Chronology Protection Agency]].
*/
class ChronologyProtector implements LoggerAwareInterface{
/** @var BagOStuff */
protected $store;
/** @var LoggerInterface */
protected $logger;
/** @var string Storage key name */
protected $key;
/** @var string Hash of client parameters */
protected $clientId;
/** @var float|null Minimum UNIX timestamp of 1+ expected startup positions */
protected $waitForPosTime;
/** @var int Max seconds to wait on positions to appear */
protected $waitForPosTimeout = self::POS_WAIT_TIMEOUT;
/** @var bool Whether to no-op all method calls */
protected $enabled = true;
/** @var bool Whether to check and wait on positions */
protected $wait = true;
/** @var bool Whether the client data was loaded */
protected $initialized = false;
/** @var DBMasterPos[] Map of (DB master name => position) */
protected $startupPositions = [];
/** @var DBMasterPos[] Map of (DB master name => position) */
protected $shutdownPositions = [];
/** @var float[] Map of (DB master name => 1) */
protected $shutdownTouchDBs = [];
/** @var integer Seconds to store positions */
const POSITION_TTL = 60;
/** @var integer Max time to wait for positions to appear */
const POS_WAIT_TIMEOUT = 5;
/**
* @param BagOStuff $store
* @param array $client Map of (ip: <IP>, agent: <user-agent>)
* @param float $posTime UNIX timestamp
* @since 1.27
*/
public function __construct( BagOStuff $store, array $client, $posTime = null ) {
$this->store = $store;
$this->clientId = md5( $client['ip'] . "\n" . $client['agent'] );
$this->key = $store->makeGlobalKey( __CLASS__, $this->clientId );
$this->waitForPosTime = $posTime;
$this->logger = new \Psr\Log\NullLogger();
}
public function setLogger( LoggerInterface $logger ) {
$this->logger = $logger;
}
/**
* @param bool $enabled Whether to no-op all method calls
* @since 1.27
*/
public function setEnabled( $enabled ) {
$this->enabled = $enabled;
}
/**
* @param bool $enabled Whether to check and wait on positions
* @since 1.27
*/
public function setWaitEnabled( $enabled ) {
$this->wait = $enabled;
}
/**
* Initialise a ILoadBalancer to give it appropriate chronology protection.
*
* If the stash has a previous master position recorded, this will try to
* make sure that the next query to a replica DB of that master will see changes up
* to that position by delaying execution. The delay may timeout and allow stale
* data if no non-lagged replica DBs are available.
*
* @param ILoadBalancer $lb
* @return void
*/
public function initLB( ILoadBalancer $lb ) {
if ( !$this->enabled || $lb->getServerCount() <= 1 ) {
return; // non-replicated setup or disabled
}
$this->initPositions();
$masterName = $lb->getServerName( $lb->getWriterIndex() );
if ( !empty( $this->startupPositions[$masterName] ) ) {
$pos = $this->startupPositions[$masterName];
$this->logger->info( __METHOD__ . ": LB for '$masterName' set to pos $pos\n" );
$lb->waitFor( $pos );
}
}
/**
* Notify the ChronologyProtector that the ILoadBalancer is about to shut
* down. Saves replication positions.
*
* @param ILoadBalancer $lb
* @return void
*/
public function shutdownLB( ILoadBalancer $lb ) {
if ( !$this->enabled ) {
return; // not enabled
} elseif ( !$lb->hasOrMadeRecentMasterChanges( INF ) ) {
// Only save the position if writes have been done on the connection
return;
}
$masterName = $lb->getServerName( $lb->getWriterIndex() );
if ( $lb->getServerCount() > 1 ) {
$pos = $lb->getMasterPos();
$this->logger->info( __METHOD__ . ": LB for '$masterName' has pos $pos\n" );
$this->shutdownPositions[$masterName] = $pos;
} else {
$this->logger->info( __METHOD__ . ": DB '$masterName' touched\n" );
}
$this->shutdownTouchDBs[$masterName] = 1;
}
/**
* Notify the ChronologyProtector that the LBFactory is done calling shutdownLB() for now.
* May commit chronology data to persistent storage.
*
* @param callable|null $workCallback Work to do instead of waiting on syncing positions
* @param string $mode One of (sync, async); whether to wait on remote datacenters
* @return DBMasterPos[] Empty on success; returns the (db name => position) map on failure
*/
public function shutdown( callable $workCallback = null, $mode = 'sync' ) {
if ( !$this->enabled ) {
return [];
}
$store = $this->store;
// Some callers might want to know if a user recently touched a DB.
// These writes do not need to block on all datacenters receiving them.
foreach ( $this->shutdownTouchDBs as $dbName => $unused ) {
$store->set(
$this->getTouchedKey( $this->store, $dbName ),
microtime( true ),
$store::TTL_DAY
);
}
if ( !count( $this->shutdownPositions ) ) {
return []; // nothing to save
}
$this->logger->info( __METHOD__ . ": saving master pos for " .
implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
);
// CP-protected writes should overwhemingly go to the master datacenter, so get DC-local
// lock to merge the values. Use a DC-local get() and a synchronous all-DC set(). This
// makes it possible for the BagOStuff class to write in parallel to all DCs with one RTT.
if ( $store->lock( $this->key, 3 ) ) {
if ( $workCallback ) {
// Let the store run the work before blocking on a replication sync barrier. By the
// time it's done with the work, the barrier should be fast if replication caught up.
$store->addBusyCallback( $workCallback );
}
$ok = $store->set(
$this->key,
self::mergePositions( $store->get( $this->key ), $this->shutdownPositions ),
self::POSITION_TTL,
( $mode === 'sync' ) ? $store::WRITE_SYNC : 0
);
$store->unlock( $this->key );
} else {
$ok = false;
}
if ( !$ok ) {
$bouncedPositions = $this->shutdownPositions;
// Raced out too many times or stash is down
$this->logger->warning( __METHOD__ . ": failed to save master pos for " .
implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
);
} elseif ( $mode === 'sync' &&
$store->getQoS( $store::ATTR_SYNCWRITES ) < $store::QOS_SYNCWRITES_BE
) {
// Positions may not be in all datacenters, force LBFactory to play it safe
$this->logger->info( __METHOD__ . ": store may not support synchronous writes." );
$bouncedPositions = $this->shutdownPositions;
} else {
$bouncedPositions = [];
}
return $bouncedPositions;
}
/**
* @param string $dbName DB master name (e.g. "db1052")
* @return float|bool UNIX timestamp when client last touched the DB; false if not on record
* @since 1.28
*/
public function getTouched( $dbName ) {
return $this->store->get( $this->getTouchedKey( $this->store, $dbName ) );
}
/**
* @param BagOStuff $store
* @param string $dbName
* @return string
*/
private function getTouchedKey( BagOStuff $store, $dbName ) {
return $store->makeGlobalKey( __CLASS__, 'mtime', $this->clientId, $dbName );
}
/**
* Load in previous master positions for the client
*/
protected function initPositions() {
if ( $this->initialized ) {
return;
}
$this->initialized = true;
if ( $this->wait ) {
// If there is an expectation to see master positions with a certain min
// timestamp, then block until they appear, or until a timeout is reached.
if ( $this->waitForPosTime > 0.0 ) {
$data = null;
$loop = new WaitConditionLoop(
function () use ( &$data ) {
$data = $this->store->get( $this->key );
return ( self::minPosTime( $data ) >= $this->waitForPosTime )
? WaitConditionLoop::CONDITION_REACHED
: WaitConditionLoop::CONDITION_CONTINUE;
},
$this->waitForPosTimeout
);
$result = $loop->invoke();
$waitedMs = $loop->getLastWaitTime() * 1e3;
if ( $result == $loop::CONDITION_REACHED ) {
$msg = "expected and found pos time {$this->waitForPosTime} ({$waitedMs}ms)";
$this->logger->debug( $msg );
} else {
$msg = "expected but missed pos time {$this->waitForPosTime} ({$waitedMs}ms)";
$this->logger->info( $msg );
}
} else {
$data = $this->store->get( $this->key );
}
$this->startupPositions = $data ? $data['positions'] : [];
$this->logger->info( __METHOD__ . ": key is {$this->key} (read)\n" );
} else {
$this->startupPositions = [];
$this->logger->info( __METHOD__ . ": key is {$this->key} (unread)\n" );
}
}
/**
* @param array|bool $data
* @return float|null
*/
private static function minPosTime( $data ) {
if ( !isset( $data['positions'] ) ) {
return null;
}
$min = null;
foreach ( $data['positions'] as $pos ) {
/** @var DBMasterPos $pos */
$min = $min ? min( $pos->asOfTime(), $min ) : $pos->asOfTime();
}
return $min;
}
/**
* @param array|bool $curValue
* @param DBMasterPos[] $shutdownPositions
* @return array
*/
private static function mergePositions( $curValue, array $shutdownPositions ) {
/** @var $curPositions DBMasterPos[] */
if ( $curValue === false ) {
$curPositions = $shutdownPositions;
} else {
$curPositions = $curValue['positions'];
// Use the newest positions for each DB master
foreach ( $shutdownPositions as $db => $pos ) {
if ( !isset( $curPositions[$db] )
|| $pos->asOfTime() > $curPositions[$db]->asOfTime()
) {
$curPositions[$db] = $pos;
}
}
}
return [ 'positions' => $curPositions ];
}
}
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