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
  24 namespace Wikimedia\Rdbms;
  25
  26 use Psr\Log\LoggerAwareInterface;
  27 use Psr\Log\LoggerInterface;
  28 use Psr\Log\NullLogger;
  29 use Wikimedia\WaitConditionLoop;
  30 use BagOStuff;
  31 use DBMasterPos;
  32 use ILoadBalancer;
  33
  34 /**
  35  * Class for ensuring a consistent ordering of events as seen by the user, despite replication.
  36  * Kind of like Hawking's [[Chronology Protection Agency]].
  37  */
  38 class ChronologyProtector implements LoggerAwareInterface {
  39         /** @var BagOStuff */
  40         protected $store;
  41         /** @var LoggerInterface */
  42         protected $logger;
  43
  44         /** @var string Storage key name */
  45         protected $key;
  46         /** @var string Hash of client parameters */
  47         protected $clientId;
  48         /** @var float|null Minimum UNIX timestamp of 1+ expected startup positions */
  49         protected $waitForPosTime;
  50         /** @var int Max seconds to wait on positions to appear */
  51         protected $waitForPosTimeout = self::POS_WAIT_TIMEOUT;
  52         /** @var bool Whether to no-op all method calls */
  53         protected $enabled = true;
  54         /** @var bool Whether to check and wait on positions */
  55         protected $wait = true;
  56
  57         /** @var bool Whether the client data was loaded */
  58         protected $initialized = false;
  59         /** @var DBMasterPos[] Map of (DB master name => position) */
  60         protected $startupPositions = [];
  61         /** @var DBMasterPos[] Map of (DB master name => position) */
  62         protected $shutdownPositions = [];
  63         /** @var float[] Map of (DB master name => 1) */
  64         protected $shutdownTouchDBs = [];
  65
  66         /** @var integer Seconds to store positions */
  67         const POSITION_TTL = 60;
  68         /** @var integer Max time to wait for positions to appear */
  69         const POS_WAIT_TIMEOUT = 5;
  70
  71         /**
  72          * @param BagOStuff $store
  73          * @param array $client Map of (ip: <IP>, agent: <user-agent>)
  74          * @param float $posTime UNIX timestamp
  75          * @since 1.27
  76          */
  77         public function __construct( BagOStuff $store, array $client, $posTime = null ) {
  78                 $this->store = $store;
  79                 $this->clientId = md5( $client['ip'] . "\n" . $client['agent'] );
  80                 $this->key = $store->makeGlobalKey( __CLASS__, $this->clientId );
  81                 $this->waitForPosTime = $posTime;
  82                 $this->logger = new NullLogger();
  83         }
  84
  85         public function setLogger( LoggerInterface $logger ) {
  86                 $this->logger = $logger;
  87         }
  88
  89         /**
  90          * @param bool $enabled Whether to no-op all method calls
  91          * @since 1.27
  92          */
  93         public function setEnabled( $enabled ) {
  94                 $this->enabled = $enabled;
  95         }
  96
  97         /**
  98          * @param bool $enabled Whether to check and wait on positions
  99          * @since 1.27
 100          */
 101         public function setWaitEnabled( $enabled ) {
 102                 $this->wait = $enabled;
 103         }
 104
 105         /**
 106          * Initialise a ILoadBalancer to give it appropriate chronology protection.
 107          *
 108          * If the stash has a previous master position recorded, this will try to
 109          * make sure that the next query to a replica DB of that master will see changes up
 110          * to that position by delaying execution. The delay may timeout and allow stale
 111          * data if no non-lagged replica DBs are available.
 112          *
 113          * @param ILoadBalancer $lb
 114          * @return void
 115          */
 116         public function initLB( ILoadBalancer $lb ) {
 117                 if ( !$this->enabled || $lb->getServerCount() <= 1 ) {
 118                         return; // non-replicated setup or disabled
 119                 }
 120
 121                 $this->initPositions();
 122
 123                 $masterName = $lb->getServerName( $lb->getWriterIndex() );
 124                 if ( !empty( $this->startupPositions[$masterName] ) ) {
 125                         $pos = $this->startupPositions[$masterName];
 126                         $this->logger->info( __METHOD__ . ": LB for '$masterName' set to pos $pos\n" );
 127                         $lb->waitFor( $pos );
 128                 }
 129         }
 130
 131         /**
 132          * Notify the ChronologyProtector that the ILoadBalancer is about to shut
 133          * down. Saves replication positions.
 134          *
 135          * @param ILoadBalancer $lb
 136          * @return void
 137          */
 138         public function shutdownLB( ILoadBalancer $lb ) {
 139                 if ( !$this->enabled ) {
 140                         return; // not enabled
 141                 } elseif ( !$lb->hasOrMadeRecentMasterChanges( INF ) ) {
 142                         // Only save the position if writes have been done on the connection
 143                         return;
 144                 }
 145
 146                 $masterName = $lb->getServerName( $lb->getWriterIndex() );
 147                 if ( $lb->getServerCount() > 1 ) {
 148                         $pos = $lb->getMasterPos();
 149                         $this->logger->info( __METHOD__ . ": LB for '$masterName' has pos $pos\n" );
 150                         $this->shutdownPositions[$masterName] = $pos;
 151                 } else {
 152                         $this->logger->info( __METHOD__ . ": DB '$masterName' touched\n" );
 153                 }
 154                 $this->shutdownTouchDBs[$masterName] = 1;
 155         }
 156
 157         /**
 158          * Notify the ChronologyProtector that the LBFactory is done calling shutdownLB() for now.
 159          * May commit chronology data to persistent storage.
 160          *
 161          * @param callable|null $workCallback Work to do instead of waiting on syncing positions
 162          * @param string $mode One of (sync, async); whether to wait on remote datacenters
 163          * @return DBMasterPos[] Empty on success; returns the (db name => position) map on failure
 164          */
 165         public function shutdown( callable $workCallback = null, $mode = 'sync' ) {
 166                 if ( !$this->enabled ) {
 167                         return [];
 168                 }
 169
 170                 $store = $this->store;
 171                 // Some callers might want to know if a user recently touched a DB.
 172                 // These writes do not need to block on all datacenters receiving them.
 173                 foreach ( $this->shutdownTouchDBs as $dbName => $unused ) {
 174                         $store->set(
 175                                 $this->getTouchedKey( $this->store, $dbName ),
 176                                 microtime( true ),
 177                                 $store::TTL_DAY
 178                         );
 179                 }
 180
 181                 if ( !count( $this->shutdownPositions ) ) {
 182                         return []; // nothing to save
 183                 }
 184
 185                 $this->logger->info( __METHOD__ . ": saving master pos for " .
 186                         implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
 187                 );
 188
 189                 // CP-protected writes should overwhemingly go to the master datacenter, so get DC-local
 190                 // lock to merge the values. Use a DC-local get() and a synchronous all-DC set(). This
 191                 // makes it possible for the BagOStuff class to write in parallel to all DCs with one RTT.
 192                 if ( $store->lock( $this->key, 3 ) ) {
 193                         if ( $workCallback ) {
 194                                 // Let the store run the work before blocking on a replication sync barrier. By the
 195                                 // time it's done with the work, the barrier should be fast if replication caught up.
 196                                 $store->addBusyCallback( $workCallback );
 197                         }
 198                         $ok = $store->set(
 199                                 $this->key,
 200                                 self::mergePositions( $store->get( $this->key ), $this->shutdownPositions ),
 201                                 self::POSITION_TTL,
 202                                 ( $mode === 'sync' ) ? $store::WRITE_SYNC : 0
 203                         );
 204                         $store->unlock( $this->key );
 205                 } else {
 206                         $ok = false;
 207                 }
 208
 209                 if ( !$ok ) {
 210                         $bouncedPositions = $this->shutdownPositions;
 211                         // Raced out too many times or stash is down
 212                         $this->logger->warning( __METHOD__ . ": failed to save master pos for " .
 213                                 implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
 214                         );
 215                 } elseif ( $mode === 'sync' &&
 216                         $store->getQoS( $store::ATTR_SYNCWRITES ) < $store::QOS_SYNCWRITES_BE
 217                 ) {
 218                         // Positions may not be in all datacenters, force LBFactory to play it safe
 219                         $this->logger->info( __METHOD__ . ": store may not support synchronous writes." );
 220                         $bouncedPositions = $this->shutdownPositions;
 221                 } else {
 222                         $bouncedPositions = [];
 223                 }
 224
 225                 return $bouncedPositions;
 226         }
 227
 228         /**
 229          * @param string $dbName DB master name (e.g. "db1052")
 230          * @return float|bool UNIX timestamp when client last touched the DB; false if not on record
 231          * @since 1.28
 232          */
 233         public function getTouched( $dbName ) {
 234                 return $this->store->get( $this->getTouchedKey( $this->store, $dbName ) );
 235         }
 236
 237         /**
 238          * @param BagOStuff $store
 239          * @param string $dbName
 240          * @return string
 241          */
 242         private function getTouchedKey( BagOStuff $store, $dbName ) {
 243                 return $store->makeGlobalKey( __CLASS__, 'mtime', $this->clientId, $dbName );
 244         }
 245
 246         /**
 247          * Load in previous master positions for the client
 248          */
 249         protected function initPositions() {
 250                 if ( $this->initialized ) {
 251                         return;
 252                 }
 253
 254                 $this->initialized = true;
 255                 if ( $this->wait ) {
 256                         // If there is an expectation to see master positions with a certain min
 257                         // timestamp, then block until they appear, or until a timeout is reached.
 258                         if ( $this->waitForPosTime > 0.0 ) {
 259                                 $data = null;
 260                                 $loop = new WaitConditionLoop(
 261                                         function () use ( &$data ) {
 262                                                 $data = $this->store->get( $this->key );
 263
 264                                                 return ( self::minPosTime( $data ) >= $this->waitForPosTime )
 265                                                         ? WaitConditionLoop::CONDITION_REACHED
 266                                                         : WaitConditionLoop::CONDITION_CONTINUE;
 267                                         },
 268                                         $this->waitForPosTimeout
 269                                 );
 270                                 $result = $loop->invoke();
 271                                 $waitedMs = $loop->getLastWaitTime() * 1e3;
 272
 273                                 if ( $result == $loop::CONDITION_REACHED ) {
 274                                         $msg = "expected and found pos time {$this->waitForPosTime} ({$waitedMs}ms)";
 275                                         $this->logger->debug( $msg );
 276                                 } else {
 277                                         $msg = "expected but missed pos time {$this->waitForPosTime} ({$waitedMs}ms)";
 278                                         $this->logger->info( $msg );
 279                                 }
 280                         } else {
 281                                 $data = $this->store->get( $this->key );
 282                         }
 283
 284                         $this->startupPositions = $data ? $data['positions'] : [];
 285                         $this->logger->info( __METHOD__ . ": key is {$this->key} (read)\n" );
 286                 } else {
 287                         $this->startupPositions = [];
 288                         $this->logger->info( __METHOD__ . ": key is {$this->key} (unread)\n" );
 289                 }
 290         }
 291
 292         /**
 293          * @param array|bool $data
 294          * @return float|null
 295          */
 296         private static function minPosTime( $data ) {
 297                 if ( !isset( $data['positions'] ) ) {
 298                         return null;
 299                 }
 300
 301                 $min = null;
 302                 foreach ( $data['positions'] as $pos ) {
 303                         /** @var DBMasterPos $pos */
 304                         $min = $min ? min( $pos->asOfTime(), $min ) : $pos->asOfTime();
 305                 }
 306
 307                 return $min;
 308         }
 309
 310         /**
 311          * @param array|bool $curValue
 312          * @param DBMasterPos[] $shutdownPositions
 313          * @return array
 314          */
 315         private static function mergePositions( $curValue, array $shutdownPositions ) {
 316                 /** @var $curPositions DBMasterPos[] */
 317                 if ( $curValue === false ) {
 318                         $curPositions = $shutdownPositions;
 319                 } else {
 320                         $curPositions = $curValue['positions'];
 321                         // Use the newest positions for each DB master
 322                         foreach ( $shutdownPositions as $db => $pos ) {
 323                                 if ( !isset( $curPositions[$db] )
 324                                         || $pos->asOfTime() > $curPositions[$db]->asOfTime()
 325                                 ) {
 326                                         $curPositions[$db] = $pos;
 327                                 }
 328                         }
 329                 }
 330
 331                 return [ 'positions' => $curPositions ];
 332         }
 333 }