includes/libs/rdbms/chronologyprotector/ChronologyProtector.php

   1 <?php
   2 /**
   3  * Generator of database load balancing objects.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Database
  22  */
  23 use Psr\Log\LoggerAwareInterface;
  24 use Psr\Log\LoggerInterface;
  25
  26 /**
  27  * Class for ensuring a consistent ordering of events as seen by the user, despite replication.
  28  * Kind of like Hawking's [[Chronology Protection Agency]].
  29  */
  30 class ChronologyProtector implements LoggerAwareInterface{
  31         /** @var BagOStuff */
  32         protected $store;
  33         /** @var LoggerInterface */
  34         protected $logger;
  35
  36         /** @var string Storage key name */
  37         protected $key;
  38         /** @var string Hash of client parameters */
  39         protected $clientId;
  40         /** @var float|null Minimum UNIX timestamp of 1+ expected startup positions */
  41         protected $waitForPosTime;
  42         /** @var int Max seconds to wait on positions to appear */
  43         protected $waitForPosTimeout = self::POS_WAIT_TIMEOUT;
  44         /** @var bool Whether to no-op all method calls */
  45         protected $enabled = true;
  46         /** @var bool Whether to check and wait on positions */
  47         protected $wait = true;
  48
  49         /** @var bool Whether the client data was loaded */
  50         protected $initialized = false;
  51         /** @var DBMasterPos[] Map of (DB master name => position) */
  52         protected $startupPositions = [];
  53         /** @var DBMasterPos[] Map of (DB master name => position) */
  54         protected $shutdownPositions = [];
  55         /** @var float[] Map of (DB master name => 1) */
  56         protected $shutdownTouchDBs = [];
  57
  58         /** @var integer Seconds to store positions */
  59         const POSITION_TTL = 60;
  60         /** @var integer Max time to wait for positions to appear */
  61         const POS_WAIT_TIMEOUT = 5;
  62
  63         /**
  64          * @param BagOStuff $store
  65          * @param array $client Map of (ip: <IP>, agent: <user-agent>)
  66          * @param float $posTime UNIX timestamp
  67          * @since 1.27
  68          */
  69         public function __construct( BagOStuff $store, array $client, $posTime = null ) {
  70                 $this->store = $store;
  71                 $this->clientId = md5( $client['ip'] . "\n" . $client['agent'] );
  72                 $this->key = $store->makeGlobalKey( __CLASS__, $this->clientId );
  73                 $this->waitForPosTime = $posTime;
  74                 $this->logger = new \Psr\Log\NullLogger();
  75         }
  76
  77         public function setLogger( LoggerInterface $logger ) {
  78                 $this->logger = $logger;
  79         }
  80
  81         /**
  82          * @param bool $enabled Whether to no-op all method calls
  83          * @since 1.27
  84          */
  85         public function setEnabled( $enabled ) {
  86                 $this->enabled = $enabled;
  87         }
  88
  89         /**
  90          * @param bool $enabled Whether to check and wait on positions
  91          * @since 1.27
  92          */
  93         public function setWaitEnabled( $enabled ) {
  94                 $this->wait = $enabled;
  95         }
  96
  97         /**
  98          * Initialise a ILoadBalancer to give it appropriate chronology protection.
  99          *
 100          * If the stash has a previous master position recorded, this will try to
 101          * make sure that the next query to a replica DB of that master will see changes up
 102          * to that position by delaying execution. The delay may timeout and allow stale
 103          * data if no non-lagged replica DBs are available.
 104          *
 105          * @param ILoadBalancer $lb
 106          * @return void
 107          */
 108         public function initLB( ILoadBalancer $lb ) {
 109                 if ( !$this->enabled || $lb->getServerCount() <= 1 ) {
 110                         return; // non-replicated setup or disabled
 111                 }
 112
 113                 $this->initPositions();
 114
 115                 $masterName = $lb->getServerName( $lb->getWriterIndex() );
 116                 if ( !empty( $this->startupPositions[$masterName] ) ) {
 117                         $pos = $this->startupPositions[$masterName];
 118                         $this->logger->info( __METHOD__ . ": LB for '$masterName' set to pos $pos\n" );
 119                         $lb->waitFor( $pos );
 120                 }
 121         }
 122
 123         /**
 124          * Notify the ChronologyProtector that the ILoadBalancer is about to shut
 125          * down. Saves replication positions.
 126          *
 127          * @param ILoadBalancer $lb
 128          * @return void
 129          */
 130         public function shutdownLB( ILoadBalancer $lb ) {
 131                 if ( !$this->enabled ) {
 132                         return; // not enabled
 133                 } elseif ( !$lb->hasOrMadeRecentMasterChanges( INF ) ) {
 134                         // Only save the position if writes have been done on the connection
 135                         return;
 136                 }
 137
 138                 $masterName = $lb->getServerName( $lb->getWriterIndex() );
 139                 if ( $lb->getServerCount() > 1 ) {
 140                         $pos = $lb->getMasterPos();
 141                         $this->logger->info( __METHOD__ . ": LB for '$masterName' has pos $pos\n" );
 142                         $this->shutdownPositions[$masterName] = $pos;
 143                 } else {
 144                         $this->logger->info( __METHOD__ . ": DB '$masterName' touched\n" );
 145                 }
 146                 $this->shutdownTouchDBs[$masterName] = 1;
 147         }
 148
 149         /**
 150          * Notify the ChronologyProtector that the LBFactory is done calling shutdownLB() for now.
 151          * May commit chronology data to persistent storage.
 152          *
 153          * @param callable|null $workCallback Work to do instead of waiting on syncing positions
 154          * @param string $mode One of (sync, async); whether to wait on remote datacenters
 155          * @return DBMasterPos[] Empty on success; returns the (db name => position) map on failure
 156          */
 157         public function shutdown( callable $workCallback = null, $mode = 'sync' ) {
 158                 if ( !$this->enabled ) {
 159                         return [];
 160                 }
 161
 162                 $store = $this->store;
 163                 // Some callers might want to know if a user recently touched a DB.
 164                 // These writes do not need to block on all datacenters receiving them.
 165                 foreach ( $this->shutdownTouchDBs as $dbName => $unused ) {
 166                         $store->set(
 167                                 $this->getTouchedKey( $this->store, $dbName ),
 168                                 microtime( true ),
 169                                 $store::TTL_DAY
 170                         );
 171                 }
 172
 173                 if ( !count( $this->shutdownPositions ) ) {
 174                         return []; // nothing to save
 175                 }
 176
 177                 $this->logger->info( __METHOD__ . ": saving master pos for " .
 178                         implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
 179                 );
 180
 181                 // CP-protected writes should overwhemingly go to the master datacenter, so get DC-local
 182                 // lock to merge the values. Use a DC-local get() and a synchronous all-DC set(). This
 183                 // makes it possible for the BagOStuff class to write in parallel to all DCs with one RTT.
 184                 if ( $store->lock( $this->key, 3 ) ) {
 185                         if ( $workCallback ) {
 186                                 // Let the store run the work before blocking on a replication sync barrier. By the
 187                                 // time it's done with the work, the barrier should be fast if replication caught up.
 188                                 $store->addBusyCallback( $workCallback );
 189                         }
 190                         $ok = $store->set(
 191                                 $this->key,
 192                                 self::mergePositions( $store->get( $this->key ), $this->shutdownPositions ),
 193                                 self::POSITION_TTL,
 194                                 ( $mode === 'sync' ) ? $store::WRITE_SYNC : 0
 195                         );
 196                         $store->unlock( $this->key );
 197                 } else {
 198                         $ok = false;
 199                 }
 200
 201                 if ( !$ok ) {
 202                         $bouncedPositions = $this->shutdownPositions;
 203                         // Raced out too many times or stash is down
 204                         $this->logger->warning( __METHOD__ . ": failed to save master pos for " .
 205                                 implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
 206                         );
 207                 } elseif ( $mode === 'sync' &&
 208                         $store->getQoS( $store::ATTR_SYNCWRITES ) < $store::QOS_SYNCWRITES_BE
 209                 ) {
 210                         // Positions may not be in all datacenters, force LBFactory to play it safe
 211                         $this->logger->info( __METHOD__ . ": store may not support synchronous writes." );
 212                         $bouncedPositions = $this->shutdownPositions;
 213                 } else {
 214                         $bouncedPositions = [];
 215                 }
 216
 217                 return $bouncedPositions;
 218         }
 219
 220         /**
 221          * @param string $dbName DB master name (e.g. "db1052")
 222          * @return float|bool UNIX timestamp when client last touched the DB; false if not on record
 223          * @since 1.28
 224          */
 225         public function getTouched( $dbName ) {
 226                 return $this->store->get( $this->getTouchedKey( $this->store, $dbName ) );
 227         }
 228
 229         /**
 230          * @param BagOStuff $store
 231          * @param string $dbName
 232          * @return string
 233          */
 234         private function getTouchedKey( BagOStuff $store, $dbName ) {
 235                 return $store->makeGlobalKey( __CLASS__, 'mtime', $this->clientId, $dbName );
 236         }
 237
 238         /**
 239          * Load in previous master positions for the client
 240          */
 241         protected function initPositions() {
 242                 if ( $this->initialized ) {
 243                         return;
 244                 }
 245
 246                 $this->initialized = true;
 247                 if ( $this->wait ) {
 248                         // If there is an expectation to see master positions with a certain min
 249                         // timestamp, then block until they appear, or until a timeout is reached.
 250                         if ( $this->waitForPosTime > 0.0 ) {
 251                                 $data = null;
 252                                 $loop = new WaitConditionLoop(
 253                                         function () use ( &$data ) {
 254                                                 $data = $this->store->get( $this->key );
 255
 256                                                 return ( self::minPosTime( $data ) >= $this->waitForPosTime )
 257                                                         ? WaitConditionLoop::CONDITION_REACHED
 258                                                         : WaitConditionLoop::CONDITION_CONTINUE;
 259                                         },
 260                                         $this->waitForPosTimeout
 261                                 );
 262                                 $result = $loop->invoke();
 263                                 $waitedMs = $loop->getLastWaitTime() * 1e3;
 264
 265                                 if ( $result == $loop::CONDITION_REACHED ) {
 266                                         $msg = "expected and found pos time {$this->waitForPosTime} ({$waitedMs}ms)";
 267                                         $this->logger->debug( $msg );
 268                                 } else {
 269                                         $msg = "expected but missed pos time {$this->waitForPosTime} ({$waitedMs}ms)";
 270                                         $this->logger->info( $msg );
 271                                 }
 272                         } else {
 273                                 $data = $this->store->get( $this->key );
 274                         }
 275
 276                         $this->startupPositions = $data ? $data['positions'] : [];
 277                         $this->logger->info( __METHOD__ . ": key is {$this->key} (read)\n" );
 278                 } else {
 279                         $this->startupPositions = [];
 280                         $this->logger->info( __METHOD__ . ": key is {$this->key} (unread)\n" );
 281                 }
 282         }
 283
 284         /**
 285          * @param array|bool $data
 286          * @return float|null
 287          */
 288         private static function minPosTime( $data ) {
 289                 if ( !isset( $data['positions'] ) ) {
 290                         return null;
 291                 }
 292
 293                 $min = null;
 294                 foreach ( $data['positions'] as $pos ) {
 295                         /** @var DBMasterPos $pos */
 296                         $min = $min ? min( $pos->asOfTime(), $min ) : $pos->asOfTime();
 297                 }
 298
 299                 return $min;
 300         }
 301
 302         /**
 303          * @param array|bool $curValue
 304          * @param DBMasterPos[] $shutdownPositions
 305          * @return array
 306          */
 307         private static function mergePositions( $curValue, array $shutdownPositions ) {
 308                 /** @var $curPositions DBMasterPos[] */
 309                 if ( $curValue === false ) {
 310                         $curPositions = $shutdownPositions;
 311                 } else {
 312                         $curPositions = $curValue['positions'];
 313                         // Use the newest positions for each DB master
 314                         foreach ( $shutdownPositions as $db => $pos ) {
 315                                 if ( !isset( $curPositions[$db] )
 316                                         || $pos->asOfTime() > $curPositions[$db]->asOfTime()
 317                                 ) {
 318                                         $curPositions[$db] = $pos;
 319                                 }
 320                         }
 321                 }
 322
 323                 return [ 'positions' => $curPositions ];
 324         }
 325 }