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
  32 /**
  33  * Class for ensuring a consistent ordering of events as seen by the user, despite replication.
  34  * Kind of like Hawking's [[Chronology Protection Agency]].
  35  */
  36 class ChronologyProtector implements LoggerAwareInterface {
  37         /** @var BagOStuff */
  38         protected $store;
  39         /** @var LoggerInterface */
  40         protected $logger;
  41
  42         /** @var string Storage key name */
  43         protected $key;
  44         /** @var string Hash of client parameters */
  45         protected $clientId;
  46         /** @var string[] Map of client information fields for logging */
  47         protected $clientInfo;
  48         /** @var int|null Expected minimum index of the last write to the position store */
  49         protected $waitForPosIndex;
  50         /** @var int Max seconds to wait on positions to appear */
  51         protected $waitForPosStoreTimeout = self::POS_STORE_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 int Seconds to store positions */
  67         const POSITION_TTL = 60;
  68         /** @var int Seconds to store position write index cookies (safely less than POSITION_TTL) */
  69         const POSITION_COOKIE_TTL = 60;
  70         /** @var int Max time to wait for positions to appear */
  71         const POS_STORE_WAIT_TIMEOUT = 5;
  72
  73         /**
  74          * @param BagOStuff $store
  75          * @param array[] $client Map of (ip: <IP>, agent: <user-agent> [, clientId: <hash>] )
  76          * @param int|null $posIndex Write counter index [optional]
  77          * @since 1.27
  78          */
  79         public function __construct( BagOStuff $store, array $client, $posIndex = null ) {
  80                 $this->store = $store;
  81                 $this->clientId = isset( $client['clientId'] )
  82                         ? $client['clientId']
  83                         : md5( $client['ip'] . "\n" . $client['agent'] );
  84                 $this->key = $store->makeGlobalKey( __CLASS__, $this->clientId, 'v2' );
  85                 $this->waitForPosIndex = $posIndex;
  86
  87                 $this->clientInfo = $client + [ 'clientId' => '' ];
  88
  89                 $this->logger = new NullLogger();
  90         }
  91
  92         public function setLogger( LoggerInterface $logger ) {
  93                 $this->logger = $logger;
  94         }
  95
  96         /**
  97          * @return string Client ID hash
  98          * @since 1.32
  99          */
 100         public function getClientId() {
 101                 return $this->clientId;
 102         }
 103
 104         /**
 105          * @param bool $enabled Whether to no-op all method calls
 106          * @since 1.27
 107          */
 108         public function setEnabled( $enabled ) {
 109                 $this->enabled = $enabled;
 110         }
 111
 112         /**
 113          * @param bool $enabled Whether to check and wait on positions
 114          * @since 1.27
 115          */
 116         public function setWaitEnabled( $enabled ) {
 117                 $this->wait = $enabled;
 118         }
 119
 120         /**
 121          * Initialise a ILoadBalancer to give it appropriate chronology protection.
 122          *
 123          * If the stash has a previous master position recorded, this will try to
 124          * make sure that the next query to a replica DB of that master will see changes up
 125          * to that position by delaying execution. The delay may timeout and allow stale
 126          * data if no non-lagged replica DBs are available.
 127          *
 128          * @param ILoadBalancer $lb
 129          * @return void
 130          */
 131         public function initLB( ILoadBalancer $lb ) {
 132                 if ( !$this->enabled || $lb->getServerCount() <= 1 ) {
 133                         return; // non-replicated setup or disabled
 134                 }
 135
 136                 $this->initPositions();
 137
 138                 $masterName = $lb->getServerName( $lb->getWriterIndex() );
 139                 if (
 140                         isset( $this->startupPositions[$masterName] ) &&
 141                         $this->startupPositions[$masterName] instanceof DBMasterPos
 142                 ) {
 143                         $pos = $this->startupPositions[$masterName];
 144                         $this->logger->debug( __METHOD__ . ": LB for '$masterName' set to pos $pos\n" );
 145                         $lb->waitFor( $pos );
 146                 }
 147         }
 148
 149         /**
 150          * Notify the ChronologyProtector that the ILoadBalancer is about to shut
 151          * down. Saves replication positions.
 152          *
 153          * @param ILoadBalancer $lb
 154          * @return void
 155          */
 156         public function shutdownLB( ILoadBalancer $lb ) {
 157                 if ( !$this->enabled ) {
 158                         return; // not enabled
 159                 } elseif ( !$lb->hasOrMadeRecentMasterChanges( INF ) ) {
 160                         // Only save the position if writes have been done on the connection
 161                         return;
 162                 }
 163
 164                 $masterName = $lb->getServerName( $lb->getWriterIndex() );
 165                 if ( $lb->getServerCount() > 1 ) {
 166                         $pos = $lb->getMasterPos();
 167                         if ( $pos ) {
 168                                 $this->logger->debug( __METHOD__ . ": LB for '$masterName' has pos $pos\n" );
 169                                 $this->shutdownPositions[$masterName] = $pos;
 170                         }
 171                 } else {
 172                         $this->logger->debug( __METHOD__ . ": DB '$masterName' touched\n" );
 173                 }
 174                 $this->shutdownTouchDBs[$masterName] = 1;
 175         }
 176
 177         /**
 178          * Notify the ChronologyProtector that the LBFactory is done calling shutdownLB() for now.
 179          * May commit chronology data to persistent storage.
 180          *
 181          * @param callable|null $workCallback Work to do instead of waiting on syncing positions
 182          * @param string $mode One of (sync, async); whether to wait on remote datacenters
 183          * @param int|null &$cpIndex DB position key write counter; incremented on update
 184          * @return DBMasterPos[] Empty on success; returns the (db name => position) map on failure
 185          */
 186         public function shutdown( callable $workCallback = null, $mode = 'sync', &$cpIndex = null ) {
 187                 if ( !$this->enabled ) {
 188                         return [];
 189                 }
 190
 191                 $store = $this->store;
 192                 // Some callers might want to know if a user recently touched a DB.
 193                 // These writes do not need to block on all datacenters receiving them.
 194                 foreach ( $this->shutdownTouchDBs as $dbName => $unused ) {
 195                         $store->set(
 196                                 $this->getTouchedKey( $this->store, $dbName ),
 197                                 microtime( true ),
 198                                 $store::TTL_DAY
 199                         );
 200                 }
 201
 202                 if ( !count( $this->shutdownPositions ) ) {
 203                         return []; // nothing to save
 204                 }
 205
 206                 $this->logger->debug( __METHOD__ . ": saving master pos for " .
 207                         implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
 208                 );
 209
 210                 // CP-protected writes should overwhelmingly go to the master datacenter, so use a
 211                 // DC-local lock to merge the values. Use a DC-local get() and a synchronous all-DC
 212                 // set(). This makes it possible for the BagOStuff class to write in parallel to all
 213                 // DCs with one RTT. The use of WRITE_SYNC avoids needing READ_LATEST for the get().
 214                 if ( $store->lock( $this->key, 3 ) ) {
 215                         if ( $workCallback ) {
 216                                 // Let the store run the work before blocking on a replication sync barrier.
 217                                 // If replication caught up while the work finished, the barrier will be fast.
 218                                 $store->addBusyCallback( $workCallback );
 219                         }
 220                         $ok = $store->set(
 221                                 $this->key,
 222                                 $this->mergePositions(
 223                                         $store->get( $this->key ),
 224                                         $this->shutdownPositions,
 225                                         $cpIndex
 226                                 ),
 227                                 self::POSITION_TTL,
 228                                 ( $mode === 'sync' ) ? $store::WRITE_SYNC : 0
 229                         );
 230                         $store->unlock( $this->key );
 231                 } else {
 232                         $ok = false;
 233                 }
 234
 235                 if ( !$ok ) {
 236                         $cpIndex = null; // nothing saved
 237                         $bouncedPositions = $this->shutdownPositions;
 238                         // Raced out too many times or stash is down
 239                         $this->logger->warning( __METHOD__ . ": failed to save master pos for " .
 240                                 implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
 241                         );
 242                 } elseif ( $mode === 'sync' &&
 243                         $store->getQoS( $store::ATTR_SYNCWRITES ) < $store::QOS_SYNCWRITES_BE
 244                 ) {
 245                         // Positions may not be in all datacenters, force LBFactory to play it safe
 246                         $this->logger->info( __METHOD__ . ": store may not support synchronous writes." );
 247                         $bouncedPositions = $this->shutdownPositions;
 248                 } else {
 249                         $bouncedPositions = [];
 250                 }
 251
 252                 return $bouncedPositions;
 253         }
 254
 255         /**
 256          * @param string $dbName DB master name (e.g. "db1052")
 257          * @return float|bool UNIX timestamp when client last touched the DB; false if not on record
 258          * @since 1.28
 259          */
 260         public function getTouched( $dbName ) {
 261                 return $this->store->get( $this->getTouchedKey( $this->store, $dbName ) );
 262         }
 263
 264         /**
 265          * @param BagOStuff $store
 266          * @param string $dbName
 267          * @return string
 268          */
 269         private function getTouchedKey( BagOStuff $store, $dbName ) {
 270                 return $store->makeGlobalKey( __CLASS__, 'mtime', $this->clientId, $dbName );
 271         }
 272
 273         /**
 274          * Load in previous master positions for the client
 275          */
 276         protected function initPositions() {
 277                 if ( $this->initialized ) {
 278                         return;
 279                 }
 280
 281                 $this->initialized = true;
 282                 if ( $this->wait ) {
 283                         // If there is an expectation to see master positions from a certain write
 284                         // index or higher, then block until it appears, or until a timeout is reached.
 285                         // Since the write index restarts each time the key is created, it is possible that
 286                         // a lagged store has a matching key write index. However, in that case, it should
 287                         // already be expired and thus treated as non-existing, maintaining correctness.
 288                         if ( $this->waitForPosIndex > 0 ) {
 289                                 $data = null;
 290                                 $indexReached = null; // highest index reached in the position store
 291                                 $loop = new WaitConditionLoop(
 292                                         function () use ( &$data, &$indexReached ) {
 293                                                 $data = $this->store->get( $this->key );
 294                                                 if ( !is_array( $data ) ) {
 295                                                         return WaitConditionLoop::CONDITION_CONTINUE; // not found yet
 296                                                 } elseif ( !isset( $data['writeIndex'] ) ) {
 297                                                         return WaitConditionLoop::CONDITION_REACHED; // b/c
 298                                                 }
 299                                                 $indexReached = max( $data['writeIndex'], $indexReached );
 300
 301                                                 return ( $data['writeIndex'] >= $this->waitForPosIndex )
 302                                                         ? WaitConditionLoop::CONDITION_REACHED
 303                                                         : WaitConditionLoop::CONDITION_CONTINUE;
 304                                         },
 305                                         $this->waitForPosStoreTimeout
 306                                 );
 307                                 $result = $loop->invoke();
 308                                 $waitedMs = $loop->getLastWaitTime() * 1e3;
 309
 310                                 if ( $result == $loop::CONDITION_REACHED ) {
 311                                         $this->logger->debug(
 312                                                 __METHOD__ . ": expected and found position index.",
 313                                                 [
 314                                                         'cpPosIndex' => $this->waitForPosIndex,
 315                                                         'waitTimeMs' => $waitedMs
 316                                                 ] + $this->clientInfo
 317                                         );
 318                                 } else {
 319                                         $this->logger->warning(
 320                                                 __METHOD__ . ": expected but failed to find position index.",
 321                                                 [
 322                                                         'cpPosIndex' => $this->waitForPosIndex,
 323                                                         'indexReached' => $indexReached,
 324                                                         'waitTimeMs' => $waitedMs
 325                                                 ] + $this->clientInfo
 326                                         );
 327                                 }
 328                         } else {
 329                                 $data = $this->store->get( $this->key );
 330                         }
 331
 332                         $this->startupPositions = $data ? $data['positions'] : [];
 333                         $this->logger->debug( __METHOD__ . ": key is {$this->key} (read)\n" );
 334                 } else {
 335                         $this->startupPositions = [];
 336                         $this->logger->debug( __METHOD__ . ": key is {$this->key} (unread)\n" );
 337                 }
 338         }
 339
 340         /**
 341          * @param array|bool $curValue
 342          * @param DBMasterPos[] $shutdownPositions
 343          * @param int|null &$cpIndex
 344          * @return array
 345          */
 346         protected function mergePositions( $curValue, array $shutdownPositions, &$cpIndex = null ) {
 347                 /** @var DBMasterPos[] $curPositions */
 348                 $curPositions = $curValue['positions'] ?? [];
 349                 // Use the newest positions for each DB master
 350                 foreach ( $shutdownPositions as $db => $pos ) {
 351                         if (
 352                                 !isset( $curPositions[$db] ) ||
 353                                 !( $curPositions[$db] instanceof DBMasterPos ) ||
 354                                 $pos->asOfTime() > $curPositions[$db]->asOfTime()
 355                         ) {
 356                                 $curPositions[$db] = $pos;
 357                         }
 358                 }
 359
 360                 $cpIndex = $curValue['writeIndex'] ?? 0;
 361
 362                 return [
 363                         'positions' => $curPositions,
 364                         'writeIndex' => ++$cpIndex
 365                 ];
 366         }
 367 }