includes/libs/rdbms/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 use Wikimedia\WaitConditionLoop;
  26
  27 /**
  28  * Class for ensuring a consistent ordering of events as seen by the user, despite replication.
  29  * Kind of like Hawking's [[Chronology Protection Agency]].
  30  */
  31 class ChronologyProtector implements LoggerAwareInterface {
  32         /** @var BagOStuff */
  33         protected $store;
  34         /** @var LoggerInterface */
  35         protected $logger;
  36
  37         /** @var string Storage key name */
  38         protected $key;
  39         /** @var string Hash of client parameters */
  40         protected $clientId;
  41         /** @var float|null Minimum UNIX timestamp of 1+ expected startup positions */
  42         protected $waitForPosTime;
  43         /** @var int Max seconds to wait on positions to appear */
  44         protected $waitForPosTimeout = self::POS_WAIT_TIMEOUT;
  45         /** @var bool Whether to no-op all method calls */
  46         protected $enabled = true;
  47         /** @var bool Whether to check and wait on positions */
  48         protected $wait = true;
  49
  50         /** @var bool Whether the client data was loaded */
  51         protected $initialized = false;
  52         /** @var DBMasterPos[] Map of (DB master name => position) */
  53         protected $startupPositions = [];
  54         /** @var DBMasterPos[] Map of (DB master name => position) */
  55         protected $shutdownPositions = [];
  56         /** @var float[] Map of (DB master name => 1) */
  57         protected $shutdownTouchDBs = [];
  58
  59         /** @var integer Seconds to store positions */
  60         const POSITION_TTL = 60;
  61         /** @var integer Max time to wait for positions to appear */
  62         const POS_WAIT_TIMEOUT = 5;
  63
  64         /**
  65          * @param BagOStuff $store
  66          * @param array $client Map of (ip: <IP>, agent: <user-agent>)
  67          * @param float $posTime UNIX timestamp
  68          * @since 1.27
  69          */
  70         public function __construct( BagOStuff $store, array $client, $posTime = null ) {
  71                 $this->store = $store;
  72                 $this->clientId = md5( $client['ip'] . "\n" . $client['agent'] );
  73                 $this->key = $store->makeGlobalKey( __CLASS__, $this->clientId );
  74                 $this->waitForPosTime = $posTime;
  75                 $this->logger = new \Psr\Log\NullLogger();
  76         }
  77
  78         public function setLogger( LoggerInterface $logger ) {
  79                 $this->logger = $logger;
  80         }
  81
  82         /**
  83          * @param bool $enabled Whether to no-op all method calls
  84          * @since 1.27
  85          */
  86         public function setEnabled( $enabled ) {
  87                 $this->enabled = $enabled;
  88         }
  89
  90         /**
  91          * @param bool $enabled Whether to check and wait on positions
  92          * @since 1.27
  93          */
  94         public function setWaitEnabled( $enabled ) {
  95                 $this->wait = $enabled;
  96         }
  97
  98         /**
  99          * Initialise a ILoadBalancer to give it appropriate chronology protection.
 100          *
 101          * If the stash has a previous master position recorded, this will try to
 102          * make sure that the next query to a replica DB of that master will see changes up
 103          * to that position by delaying execution. The delay may timeout and allow stale
 104          * data if no non-lagged replica DBs are available.
 105          *
 106          * @param ILoadBalancer $lb
 107          * @return void
 108          */
 109         public function initLB( ILoadBalancer $lb ) {
 110                 if ( !$this->enabled || $lb->getServerCount() <= 1 ) {
 111                         return; // non-replicated setup or disabled
 112                 }
 113
 114                 $this->initPositions();
 115
 116                 $masterName = $lb->getServerName( $lb->getWriterIndex() );
 117                 if ( !empty( $this->startupPositions[$masterName] ) ) {
 118                         $pos = $this->startupPositions[$masterName];
 119                         $this->logger->info( __METHOD__ . ": LB for '$masterName' set to pos $pos\n" );
 120                         $lb->waitFor( $pos );
 121                 }
 122         }
 123
 124         /**
 125          * Notify the ChronologyProtector that the ILoadBalancer is about to shut
 126          * down. Saves replication positions.
 127          *
 128          * @param ILoadBalancer $lb
 129          * @return void
 130          */
 131         public function shutdownLB( ILoadBalancer $lb ) {
 132                 if ( !$this->enabled ) {
 133                         return; // not enabled
 134                 } elseif ( !$lb->hasOrMadeRecentMasterChanges( INF ) ) {
 135                         // Only save the position if writes have been done on the connection
 136                         return;
 137                 }
 138
 139                 $masterName = $lb->getServerName( $lb->getWriterIndex() );
 140                 if ( $lb->getServerCount() > 1 ) {
 141                         $pos = $lb->getMasterPos();
 142                         $this->logger->info( __METHOD__ . ": LB for '$masterName' has pos $pos\n" );
 143                         $this->shutdownPositions[$masterName] = $pos;
 144                 } else {
 145                         $this->logger->info( __METHOD__ . ": DB '$masterName' touched\n" );
 146                 }
 147                 $this->shutdownTouchDBs[$masterName] = 1;
 148         }
 149
 150         /**
 151          * Notify the ChronologyProtector that the LBFactory is done calling shutdownLB() for now.
 152          * May commit chronology data to persistent storage.
 153          *
 154          * @param callable|null $workCallback Work to do instead of waiting on syncing positions
 155          * @param string $mode One of (sync, async); whether to wait on remote datacenters
 156          * @return DBMasterPos[] Empty on success; returns the (db name => position) map on failure
 157          */
 158         public function shutdown( callable $workCallback = null, $mode = 'sync' ) {
 159                 if ( !$this->enabled ) {
 160                         return [];
 161                 }
 162
 163                 $store = $this->store;
 164                 // Some callers might want to know if a user recently touched a DB.
 165                 // These writes do not need to block on all datacenters receiving them.
 166                 foreach ( $this->shutdownTouchDBs as $dbName => $unused ) {
 167                         $store->set(
 168                                 $this->getTouchedKey( $this->store, $dbName ),
 169                                 microtime( true ),
 170                                 $store::TTL_DAY
 171                         );
 172                 }
 173
 174                 if ( !count( $this->shutdownPositions ) ) {
 175                         return []; // nothing to save
 176                 }
 177
 178                 $this->logger->info( __METHOD__ . ": saving master pos for " .
 179                         implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
 180                 );
 181
 182                 // CP-protected writes should overwhemingly go to the master datacenter, so get DC-local
 183                 // lock to merge the values. Use a DC-local get() and a synchronous all-DC set(). This
 184                 // makes it possible for the BagOStuff class to write in parallel to all DCs with one RTT.
 185                 if ( $store->lock( $this->key, 3 ) ) {
 186                         if ( $workCallback ) {
 187                                 // Let the store run the work before blocking on a replication sync barrier. By the
 188                                 // time it's done with the work, the barrier should be fast if replication caught up.
 189                                 $store->addBusyCallback( $workCallback );
 190                         }
 191                         $ok = $store->set(
 192                                 $this->key,
 193                                 self::mergePositions( $store->get( $this->key ), $this->shutdownPositions ),
 194                                 self::POSITION_TTL,
 195                                 ( $mode === 'sync' ) ? $store::WRITE_SYNC : 0
 196                         );
 197                         $store->unlock( $this->key );
 198                 } else {
 199                         $ok = false;
 200                 }
 201
 202                 if ( !$ok ) {
 203                         $bouncedPositions = $this->shutdownPositions;
 204                         // Raced out too many times or stash is down
 205                         $this->logger->warning( __METHOD__ . ": failed to save master pos for " .
 206                                 implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
 207                         );
 208                 } elseif ( $mode === 'sync' &&
 209                         $store->getQoS( $store::ATTR_SYNCWRITES ) < $store::QOS_SYNCWRITES_BE
 210                 ) {
 211                         // Positions may not be in all datacenters, force LBFactory to play it safe
 212                         $this->logger->info( __METHOD__ . ": store may not support synchronous writes." );
 213                         $bouncedPositions = $this->shutdownPositions;
 214                 } else {
 215                         $bouncedPositions = [];
 216                 }
 217
 218                 return $bouncedPositions;
 219         }
 220
 221         /**
 222          * @param string $dbName DB master name (e.g. "db1052")
 223          * @return float|bool UNIX timestamp when client last touched the DB; false if not on record
 224          * @since 1.28
 225          */
 226         public function getTouched( $dbName ) {
 227                 return $this->store->get( $this->getTouchedKey( $this->store, $dbName ) );
 228         }
 229
 230         /**
 231          * @param BagOStuff $store
 232          * @param string $dbName
 233          * @return string
 234          */
 235         private function getTouchedKey( BagOStuff $store, $dbName ) {
 236                 return $store->makeGlobalKey( __CLASS__, 'mtime', $this->clientId, $dbName );
 237         }
 238
 239         /**
 240          * Load in previous master positions for the client
 241          */
 242         protected function initPositions() {
 243                 if ( $this->initialized ) {
 244                         return;
 245                 }
 246
 247                 $this->initialized = true;
 248                 if ( $this->wait ) {
 249                         // If there is an expectation to see master positions with a certain min
 250                         // timestamp, then block until they appear, or until a timeout is reached.
 251                         if ( $this->waitForPosTime > 0.0 ) {
 252                                 $data = null;
 253                                 $loop = new WaitConditionLoop(
 254                                         function () use ( &$data ) {
 255                                                 $data = $this->store->get( $this->key );
 256
 257                                                 return ( self::minPosTime( $data ) >= $this->waitForPosTime )
 258                                                         ? WaitConditionLoop::CONDITION_REACHED
 259                                                         : WaitConditionLoop::CONDITION_CONTINUE;
 260                                         },
 261                                         $this->waitForPosTimeout
 262                                 );
 263                                 $result = $loop->invoke();
 264                                 $waitedMs = $loop->getLastWaitTime() * 1e3;
 265
 266                                 if ( $result == $loop::CONDITION_REACHED ) {
 267                                         $msg = "expected and found pos time {$this->waitForPosTime} ({$waitedMs}ms)";
 268                                         $this->logger->debug( $msg );
 269                                 } else {
 270                                         $msg = "expected but missed pos time {$this->waitForPosTime} ({$waitedMs}ms)";
 271                                         $this->logger->info( $msg );
 272                                 }
 273                         } else {
 274                                 $data = $this->store->get( $this->key );
 275                         }
 276
 277                         $this->startupPositions = $data ? $data['positions'] : [];
 278                         $this->logger->info( __METHOD__ . ": key is {$this->key} (read)\n" );
 279                 } else {
 280                         $this->startupPositions = [];
 281                         $this->logger->info( __METHOD__ . ": key is {$this->key} (unread)\n" );
 282                 }
 283         }
 284
 285         /**
 286          * @param array|bool $data
 287          * @return float|null
 288          */
 289         private static function minPosTime( $data ) {
 290                 if ( !isset( $data['positions'] ) ) {
 291                         return null;
 292                 }
 293
 294                 $min = null;
 295                 foreach ( $data['positions'] as $pos ) {
 296                         /** @var DBMasterPos $pos */
 297                         $min = $min ? min( $pos->asOfTime(), $min ) : $pos->asOfTime();
 298                 }
 299
 300                 return $min;
 301         }
 302
 303         /**
 304          * @param array|bool $curValue
 305          * @param DBMasterPos[] $shutdownPositions
 306          * @return array
 307          */
 308         private static function mergePositions( $curValue, array $shutdownPositions ) {
 309                 /** @var $curPositions DBMasterPos[] */
 310                 if ( $curValue === false ) {
 311                         $curPositions = $shutdownPositions;
 312                 } else {
 313                         $curPositions = $curValue['positions'];
 314                         // Use the newest positions for each DB master
 315                         foreach ( $shutdownPositions as $db => $pos ) {
 316                                 if ( !isset( $curPositions[$db] )
 317                                         || $pos->asOfTime() > $curPositions[$db]->asOfTime()
 318                                 ) {
 319                                         $curPositions[$db] = $pos;
 320                                 }
 321                         }
 322                 }
 323
 324                 return [ 'positions' => $curPositions ];
 325         }
 326 }