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 $clientLogInfo;
  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 = 10;
  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 = $client['clientId'] ??
  82                         md5( $client['ip'] . "\n" . $client['agent'] );
  83                 $this->key = $store->makeGlobalKey( __CLASS__, $this->clientId, 'v2' );
  84                 $this->waitForPosIndex = $posIndex;
  85
  86                 $this->clientLogInfo = [
  87                         'clientIP' => $client['ip'],
  88                         'clientAgent' => $client['agent'],
  89                         'clientId' => $client['clientId'] ?? null
  90                 ];
  91
  92                 $this->logger = new NullLogger();
  93         }
  94
  95         public function setLogger( LoggerInterface $logger ) {
  96                 $this->logger = $logger;
  97         }
  98
  99         /**
 100          * @return string Client ID hash
 101          * @since 1.32
 102          */
 103         public function getClientId() {
 104                 return $this->clientId;
 105         }
 106
 107         /**
 108          * @param bool $enabled Whether to no-op all method calls
 109          * @since 1.27
 110          */
 111         public function setEnabled( $enabled ) {
 112                 $this->enabled = $enabled;
 113         }
 114
 115         /**
 116          * @param bool $enabled Whether to check and wait on positions
 117          * @since 1.27
 118          */
 119         public function setWaitEnabled( $enabled ) {
 120                 $this->wait = $enabled;
 121         }
 122
 123         /**
 124          * Initialise a ILoadBalancer to give it appropriate chronology protection.
 125          *
 126          * If the stash has a previous master position recorded, this will try to
 127          * make sure that the next query to a replica DB of that master will see changes up
 128          * to that position by delaying execution. The delay may timeout and allow stale
 129          * data if no non-lagged replica DBs are available.
 130          *
 131          * @param ILoadBalancer $lb
 132          * @return void
 133          */
 134         public function initLB( ILoadBalancer $lb ) {
 135                 if ( !$this->enabled || $lb->getServerCount() <= 1 ) {
 136                         return; // non-replicated setup or disabled
 137                 }
 138
 139                 $this->initPositions();
 140
 141                 $masterName = $lb->getServerName( $lb->getWriterIndex() );
 142                 if (
 143                         isset( $this->startupPositions[$masterName] ) &&
 144                         $this->startupPositions[$masterName] instanceof DBMasterPos
 145                 ) {
 146                         $pos = $this->startupPositions[$masterName];
 147                         $this->logger->debug( __METHOD__ . ": LB for '$masterName' set to pos $pos\n" );
 148                         $lb->waitFor( $pos );
 149                 }
 150         }
 151
 152         /**
 153          * Notify the ChronologyProtector that the ILoadBalancer is about to shut
 154          * down. Saves replication positions.
 155          *
 156          * @param ILoadBalancer $lb
 157          * @return void
 158          */
 159         public function shutdownLB( ILoadBalancer $lb ) {
 160                 if ( !$this->enabled ) {
 161                         return; // not enabled
 162                 } elseif ( !$lb->hasOrMadeRecentMasterChanges( INF ) ) {
 163                         // Only save the position if writes have been done on the connection
 164                         return;
 165                 }
 166
 167                 $masterName = $lb->getServerName( $lb->getWriterIndex() );
 168                 if ( $lb->getServerCount() > 1 ) {
 169                         $pos = $lb->getMasterPos();
 170                         if ( $pos ) {
 171                                 $this->logger->debug( __METHOD__ . ": LB for '$masterName' has pos $pos\n" );
 172                                 $this->shutdownPositions[$masterName] = $pos;
 173                         }
 174                 } else {
 175                         $this->logger->debug( __METHOD__ . ": DB '$masterName' touched\n" );
 176                 }
 177                 $this->shutdownTouchDBs[$masterName] = 1;
 178         }
 179
 180         /**
 181          * Notify the ChronologyProtector that the LBFactory is done calling shutdownLB() for now.
 182          * May commit chronology data to persistent storage.
 183          *
 184          * @param callable|null $workCallback Work to do instead of waiting on syncing positions
 185          * @param string $mode One of (sync, async); whether to wait on remote datacenters
 186          * @param int|null &$cpIndex DB position key write counter; incremented on update
 187          * @return DBMasterPos[] Empty on success; returns the (db name => position) map on failure
 188          */
 189         public function shutdown( callable $workCallback = null, $mode = 'sync', &$cpIndex = null ) {
 190                 if ( !$this->enabled ) {
 191                         return [];
 192                 }
 193
 194                 $store = $this->store;
 195                 // Some callers might want to know if a user recently touched a DB.
 196                 // These writes do not need to block on all datacenters receiving them.
 197                 foreach ( $this->shutdownTouchDBs as $dbName => $unused ) {
 198                         $store->set(
 199                                 $this->getTouchedKey( $this->store, $dbName ),
 200                                 microtime( true ),
 201                                 $store::TTL_DAY
 202                         );
 203                 }
 204
 205                 if ( !count( $this->shutdownPositions ) ) {
 206                         return []; // nothing to save
 207                 }
 208
 209                 $this->logger->debug( __METHOD__ . ": saving master pos for " .
 210                         implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
 211                 );
 212
 213                 // CP-protected writes should overwhelmingly go to the master datacenter, so use a
 214                 // DC-local lock to merge the values. Use a DC-local get() and a synchronous all-DC
 215                 // set(). This makes it possible for the BagOStuff class to write in parallel to all
 216                 // DCs with one RTT. The use of WRITE_SYNC avoids needing READ_LATEST for the get().
 217                 if ( $store->lock( $this->key, 3 ) ) {
 218                         if ( $workCallback ) {
 219                                 // Let the store run the work before blocking on a replication sync barrier.
 220                                 // If replication caught up while the work finished, the barrier will be fast.
 221                                 $store->addBusyCallback( $workCallback );
 222                         }
 223                         $ok = $store->set(
 224                                 $this->key,
 225                                 $this->mergePositions(
 226                                         $store->get( $this->key ),
 227                                         $this->shutdownPositions,
 228                                         $cpIndex
 229                                 ),
 230                                 self::POSITION_TTL,
 231                                 ( $mode === 'sync' ) ? $store::WRITE_SYNC : 0
 232                         );
 233                         $store->unlock( $this->key );
 234                 } else {
 235                         $ok = false;
 236                 }
 237
 238                 if ( !$ok ) {
 239                         $cpIndex = null; // nothing saved
 240                         $bouncedPositions = $this->shutdownPositions;
 241                         // Raced out too many times or stash is down
 242                         $this->logger->warning( __METHOD__ . ": failed to save master pos for " .
 243                                 implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
 244                         );
 245                 } elseif ( $mode === 'sync' &&
 246                         $store->getQoS( $store::ATTR_SYNCWRITES ) < $store::QOS_SYNCWRITES_BE
 247                 ) {
 248                         // Positions may not be in all datacenters, force LBFactory to play it safe
 249                         $this->logger->info( __METHOD__ . ": store may not support synchronous writes." );
 250                         $bouncedPositions = $this->shutdownPositions;
 251                 } else {
 252                         $bouncedPositions = [];
 253                 }
 254
 255                 return $bouncedPositions;
 256         }
 257
 258         /**
 259          * @param string $dbName DB master name (e.g. "db1052")
 260          * @return float|bool UNIX timestamp when client last touched the DB; false if not on record
 261          * @since 1.28
 262          */
 263         public function getTouched( $dbName ) {
 264                 return $this->store->get( $this->getTouchedKey( $this->store, $dbName ) );
 265         }
 266
 267         /**
 268          * @param BagOStuff $store
 269          * @param string $dbName
 270          * @return string
 271          */
 272         private function getTouchedKey( BagOStuff $store, $dbName ) {
 273                 return $store->makeGlobalKey( __CLASS__, 'mtime', $this->clientId, $dbName );
 274         }
 275
 276         /**
 277          * Load in previous master positions for the client
 278          */
 279         protected function initPositions() {
 280                 if ( $this->initialized ) {
 281                         return;
 282                 }
 283
 284                 $this->initialized = true;
 285                 if ( $this->wait ) {
 286                         // If there is an expectation to see master positions from a certain write
 287                         // index or higher, then block until it appears, or until a timeout is reached.
 288                         // Since the write index restarts each time the key is created, it is possible that
 289                         // a lagged store has a matching key write index. However, in that case, it should
 290                         // already be expired and thus treated as non-existing, maintaining correctness.
 291                         if ( $this->waitForPosIndex > 0 ) {
 292                                 $data = null;
 293                                 $indexReached = null; // highest index reached in the position store
 294                                 $loop = new WaitConditionLoop(
 295                                         function () use ( &$data, &$indexReached ) {
 296                                                 $data = $this->store->get( $this->key );
 297                                                 if ( !is_array( $data ) ) {
 298                                                         return WaitConditionLoop::CONDITION_CONTINUE; // not found yet
 299                                                 } elseif ( !isset( $data['writeIndex'] ) ) {
 300                                                         return WaitConditionLoop::CONDITION_REACHED; // b/c
 301                                                 }
 302                                                 $indexReached = max( $data['writeIndex'], $indexReached );
 303
 304                                                 return ( $data['writeIndex'] >= $this->waitForPosIndex )
 305                                                         ? WaitConditionLoop::CONDITION_REACHED
 306                                                         : WaitConditionLoop::CONDITION_CONTINUE;
 307                                         },
 308                                         $this->waitForPosStoreTimeout
 309                                 );
 310                                 $result = $loop->invoke();
 311                                 $waitedMs = $loop->getLastWaitTime() * 1e3;
 312
 313                                 if ( $result == $loop::CONDITION_REACHED ) {
 314                                         $this->logger->debug(
 315                                                 __METHOD__ . ": expected and found position index.",
 316                                                 [
 317                                                         'cpPosIndex' => $this->waitForPosIndex,
 318                                                         'waitTimeMs' => $waitedMs
 319                                                 ] + $this->clientLogInfo
 320                                         );
 321                                 } else {
 322                                         $this->logger->warning(
 323                                                 __METHOD__ . ": expected but failed to find position index.",
 324                                                 [
 325                                                         'cpPosIndex' => $this->waitForPosIndex,
 326                                                         'indexReached' => $indexReached,
 327                                                         'waitTimeMs' => $waitedMs
 328                                                 ] + $this->clientLogInfo
 329                                         );
 330                                 }
 331                         } else {
 332                                 $data = $this->store->get( $this->key );
 333                         }
 334
 335                         $this->startupPositions = $data ? $data['positions'] : [];
 336                         $this->logger->debug( __METHOD__ . ": key is {$this->key} (read)\n" );
 337                 } else {
 338                         $this->startupPositions = [];
 339                         $this->logger->debug( __METHOD__ . ": key is {$this->key} (unread)\n" );
 340                 }
 341         }
 342
 343         /**
 344          * @param array|bool $curValue
 345          * @param DBMasterPos[] $shutdownPositions
 346          * @param int|null &$cpIndex
 347          * @return array
 348          */
 349         protected function mergePositions( $curValue, array $shutdownPositions, &$cpIndex = null ) {
 350                 /** @var DBMasterPos[] $curPositions */
 351                 $curPositions = $curValue['positions'] ?? [];
 352                 // Use the newest positions for each DB master
 353                 foreach ( $shutdownPositions as $db => $pos ) {
 354                         if (
 355                                 !isset( $curPositions[$db] ) ||
 356                                 !( $curPositions[$db] instanceof DBMasterPos ) ||
 357                                 $pos->asOfTime() > $curPositions[$db]->asOfTime()
 358                         ) {
 359                                 $curPositions[$db] = $pos;
 360                         }
 361                 }
 362
 363                 $cpIndex = $curValue['writeIndex'] ?? 0;
 364
 365                 return [
 366                         'positions' => $curPositions,
 367                         'writeIndex' => ++$cpIndex
 368                 ];
 369         }
 370 }