includes/libs/rdbms/loadbalancer/LoadBalancer.php

   1 <?php
   2 /**
   3  * Database load balancing manager
   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  */
  22 namespace Wikimedia\Rdbms;
  23
  24 use Psr\Log\LoggerInterface;
  25 use Psr\Log\NullLogger;
  26 use Wikimedia\ScopedCallback;
  27 use BagOStuff;
  28 use EmptyBagOStuff;
  29 use WANObjectCache;
  30 use ArrayUtils;
  31 use InvalidArgumentException;
  32 use RuntimeException;
  33 use Exception;
  34
  35 /**
  36  * Database connection, tracking, load balancing, and transaction manager for a cluster
  37  *
  38  * @ingroup Database
  39  */
  40 class LoadBalancer implements ILoadBalancer {
  41         /** @var array[] Map of (server index => server config array) */
  42         private $mServers;
  43         /** @var Database[][][] Map of (connection category => server index => IDatabase[]) */
  44         private $mConns;
  45         /** @var float[] Map of (server index => weight) */
  46         private $mLoads;
  47         /** @var array[] Map of (group => server index => weight) */
  48         private $mGroupLoads;
  49         /** @var bool Whether to disregard replica DB lag as a factor in replica DB selection */
  50         private $mAllowLagged;
  51         /** @var int Seconds to spend waiting on replica DB lag to resolve */
  52         private $mWaitTimeout;
  53         /** @var array The LoadMonitor configuration */
  54         private $loadMonitorConfig;
  55         /** @var array[] $aliases Map of (table => (dbname, schema, prefix) map) */
  56         private $tableAliases = [];
  57
  58         /** @var ILoadMonitor */
  59         private $loadMonitor;
  60         /** @var ChronologyProtector|null */
  61         private $chronProt;
  62         /** @var BagOStuff */
  63         private $srvCache;
  64         /** @var WANObjectCache */
  65         private $wanCache;
  66         /** @var object|string Class name or object With profileIn/profileOut methods */
  67         protected $profiler;
  68         /** @var TransactionProfiler */
  69         protected $trxProfiler;
  70         /** @var LoggerInterface */
  71         protected $replLogger;
  72         /** @var LoggerInterface */
  73         protected $connLogger;
  74         /** @var LoggerInterface */
  75         protected $queryLogger;
  76         /** @var LoggerInterface */
  77         protected $perfLogger;
  78
  79         /** @var Database DB connection object that caused a problem */
  80         private $errorConnection;
  81         /** @var int The generic (not query grouped) replica DB index (of $mServers) */
  82         private $mReadIndex;
  83         /** @var bool|DBMasterPos False if not set */
  84         private $mWaitForPos;
  85         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  86         private $laggedReplicaMode = false;
  87         /** @var bool Whether the generic reader fell back to a lagged replica DB */
  88         private $allReplicasDownMode = false;
  89         /** @var string The last DB selection or connection error */
  90         private $mLastError = 'Unknown error';
  91         /** @var string|bool Reason the LB is read-only or false if not */
  92         private $readOnlyReason = false;
  93         /** @var int Total connections opened */
  94         private $connsOpened = 0;
  95         /** @var string|bool String if a requested DBO_TRX transaction round is active */
  96         private $trxRoundId = false;
  97         /** @var array[] Map of (name => callable) */
  98         private $trxRecurringCallbacks = [];
  99         /** @var DatabaseDomain Local Domain ID and default for selectDB() calls */
 100         private $localDomain;
 101         /** @var string Alternate ID string for the domain instead of DatabaseDomain::getId() */
 102         private $localDomainIdAlias;
 103         /** @var string Current server name */
 104         private $host;
 105         /** @var bool Whether this PHP instance is for a CLI script */
 106         protected $cliMode;
 107         /** @var string Agent name for query profiling */
 108         protected $agent;
 109
 110         /** @var callable Exception logger */
 111         private $errorLogger;
 112
 113         /** @var bool */
 114         private $disabled = false;
 115         /** @var bool */
 116         private $chronProtInitialized = false;
 117         /** @var int */
 118         private $maxLag = self::MAX_LAG_DEFAULT;
 119
 120         /** @var int Warn when this many connection are held */
 121         const CONN_HELD_WARN_THRESHOLD = 10;
 122
 123         /** @var int Default 'maxLag' when unspecified */
 124         const MAX_LAG_DEFAULT = 10;
 125         /** @var int Seconds to cache master server read-only status */
 126         const TTL_CACHE_READONLY = 5;
 127
 128         const KEY_LOCAL = 'local';
 129         const KEY_FOREIGN_FREE = 'foreignFree';
 130         const KEY_FOREIGN_INUSE = 'foreignInUse';
 131
 132         const KEY_LOCAL_NOROUND = 'localAutoCommit';
 133         const KEY_FOREIGN_FREE_NOROUND = 'foreignFreeAutoCommit';
 134         const KEY_FOREIGN_INUSE_NOROUND = 'foreignInUseAutoCommit';
 135
 136         public function __construct( array $params ) {
 137                 if ( !isset( $params['servers'] ) ) {
 138                         throw new InvalidArgumentException( __CLASS__ . ': missing servers parameter' );
 139                 }
 140                 $this->mServers = $params['servers'];
 141                 foreach ( $this->mServers as $i => $server ) {
 142                         if ( $i == 0 ) {
 143                                 $this->mServers[$i]['master'] = true;
 144                         } else {
 145                                 $this->mServers[$i]['replica'] = true;
 146                         }
 147                 }
 148
 149                 $this->localDomain = isset( $params['localDomain'] )
 150                         ? DatabaseDomain::newFromId( $params['localDomain'] )
 151                         : DatabaseDomain::newUnspecified();
 152                 // In case a caller assumes that the domain ID is simply <db>-<prefix>, which is almost
 153                 // always true, gracefully handle the case when they fail to account for escaping.
 154                 if ( $this->localDomain->getTablePrefix() != '' ) {
 155                         $this->localDomainIdAlias =
 156                                 $this->localDomain->getDatabase() . '-' . $this->localDomain->getTablePrefix();
 157                 } else {
 158                         $this->localDomainIdAlias = $this->localDomain->getDatabase();
 159                 }
 160
 161                 $this->mWaitTimeout = isset( $params['waitTimeout'] ) ? $params['waitTimeout'] : 10;
 162
 163                 $this->mReadIndex = -1;
 164                 $this->mConns = [
 165                         // Connection were transaction rounds may be applied
 166                         self::KEY_LOCAL => [],
 167                         self::KEY_FOREIGN_INUSE => [],
 168                         self::KEY_FOREIGN_FREE => [],
 169                         // Auto-committing counterpart connections that ignore transaction rounds
 170                         self::KEY_LOCAL_NOROUND => [],
 171                         self::KEY_FOREIGN_INUSE_NOROUND => [],
 172                         self::KEY_FOREIGN_FREE_NOROUND => []
 173                 ];
 174                 $this->mLoads = [];
 175                 $this->mWaitForPos = false;
 176                 $this->mAllowLagged = false;
 177
 178                 if ( isset( $params['readOnlyReason'] ) && is_string( $params['readOnlyReason'] ) ) {
 179                         $this->readOnlyReason = $params['readOnlyReason'];
 180                 }
 181
 182                 if ( isset( $params['maxLag'] ) ) {
 183                         $this->maxLag = $params['maxLag'];
 184                 }
 185
 186                 if ( isset( $params['loadMonitor'] ) ) {
 187                         $this->loadMonitorConfig = $params['loadMonitor'];
 188                 } else {
 189                         $this->loadMonitorConfig = [ 'class' => 'LoadMonitorNull' ];
 190                 }
 191                 $this->loadMonitorConfig += [ 'lagWarnThreshold' => $this->maxLag ];
 192
 193                 foreach ( $params['servers'] as $i => $server ) {
 194                         $this->mLoads[$i] = $server['load'];
 195                         if ( isset( $server['groupLoads'] ) ) {
 196                                 foreach ( $server['groupLoads'] as $group => $ratio ) {
 197                                         if ( !isset( $this->mGroupLoads[$group] ) ) {
 198                                                 $this->mGroupLoads[$group] = [];
 199                                         }
 200                                         $this->mGroupLoads[$group][$i] = $ratio;
 201                                 }
 202                         }
 203                 }
 204
 205                 if ( isset( $params['srvCache'] ) ) {
 206                         $this->srvCache = $params['srvCache'];
 207                 } else {
 208                         $this->srvCache = new EmptyBagOStuff();
 209                 }
 210                 if ( isset( $params['wanCache'] ) ) {
 211                         $this->wanCache = $params['wanCache'];
 212                 } else {
 213                         $this->wanCache = WANObjectCache::newEmpty();
 214                 }
 215                 $this->profiler = isset( $params['profiler'] ) ? $params['profiler'] : null;
 216                 if ( isset( $params['trxProfiler'] ) ) {
 217                         $this->trxProfiler = $params['trxProfiler'];
 218                 } else {
 219                         $this->trxProfiler = new TransactionProfiler();
 220                 }
 221
 222                 $this->errorLogger = isset( $params['errorLogger'] )
 223                         ? $params['errorLogger']
 224                         : function ( Exception $e ) {
 225                                 trigger_error( get_class( $e ) . ': ' . $e->getMessage(), E_USER_WARNING );
 226                         };
 227
 228                 foreach ( [ 'replLogger', 'connLogger', 'queryLogger', 'perfLogger' ] as $key ) {
 229                         $this->$key = isset( $params[$key] ) ? $params[$key] : new NullLogger();
 230                 }
 231
 232                 $this->host = isset( $params['hostname'] )
 233                         ? $params['hostname']
 234                         : ( gethostname() ?: 'unknown' );
 235                 $this->cliMode = isset( $params['cliMode'] )
 236                         ? $params['cliMode']
 237                         : ( PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg' );
 238                 $this->agent = isset( $params['agent'] ) ? $params['agent'] : '';
 239
 240                 if ( isset( $params['chronologyProtector'] ) ) {
 241                         $this->chronProt = $params['chronologyProtector'];
 242                 }
 243         }
 244
 245         /**
 246          * Get the local (and default) database domain ID of connection handles
 247          *
 248          * @see DatabaseDomain
 249          * @return string Database domain ID; this specifies DB name, schema, and table prefix
 250          * @since 1.31
 251          */
 252         public function getLocalDomainID() {
 253                 return $this->localDomain->getId();
 254         }
 255
 256         /**
 257          * Get a LoadMonitor instance
 258          *
 259          * @return ILoadMonitor
 260          */
 261         private function getLoadMonitor() {
 262                 if ( !isset( $this->loadMonitor ) ) {
 263                         $compat = [
 264                                 'LoadMonitor' => LoadMonitor::class,
 265                                 'LoadMonitorNull' => LoadMonitorNull::class,
 266                                 'LoadMonitorMySQL' => LoadMonitorMySQL::class,
 267                         ];
 268
 269                         $class = $this->loadMonitorConfig['class'];
 270                         if ( isset( $compat[$class] ) ) {
 271                                 $class = $compat[$class];
 272                         }
 273
 274                         $this->loadMonitor = new $class(
 275                                 $this, $this->srvCache, $this->wanCache, $this->loadMonitorConfig );
 276                         $this->loadMonitor->setLogger( $this->replLogger );
 277                 }
 278
 279                 return $this->loadMonitor;
 280         }
 281
 282         /**
 283          * @param array $loads
 284          * @param bool|string $domain Domain to get non-lagged for
 285          * @param int $maxLag Restrict the maximum allowed lag to this many seconds
 286          * @return bool|int|string
 287          */
 288         private function getRandomNonLagged( array $loads, $domain = false, $maxLag = INF ) {
 289                 $lags = $this->getLagTimes( $domain );
 290
 291                 # Unset excessively lagged servers
 292                 foreach ( $lags as $i => $lag ) {
 293                         if ( $i != 0 ) {
 294                                 # How much lag this server nominally is allowed to have
 295                                 $maxServerLag = isset( $this->mServers[$i]['max lag'] )
 296                                         ? $this->mServers[$i]['max lag']
 297                                         : $this->maxLag; // default
 298                                 # Constrain that futher by $maxLag argument
 299                                 $maxServerLag = min( $maxServerLag, $maxLag );
 300
 301                                 $host = $this->getServerName( $i );
 302                                 if ( $lag === false && !is_infinite( $maxServerLag ) ) {
 303                                         $this->replLogger->error(
 304                                                 "Server {host} is not replicating?", [ 'host' => $host ] );
 305                                         unset( $loads[$i] );
 306                                 } elseif ( $lag > $maxServerLag ) {
 307                                         $this->replLogger->info(
 308                                                 "Server {host} has {lag} seconds of lag (>= {maxlag})",
 309                                                 [ 'host' => $host, 'lag' => $lag, 'maxlag' => $maxServerLag ]
 310                                         );
 311                                         unset( $loads[$i] );
 312                                 }
 313                         }
 314                 }
 315
 316                 # Find out if all the replica DBs with non-zero load are lagged
 317                 $sum = 0;
 318                 foreach ( $loads as $load ) {
 319                         $sum += $load;
 320                 }
 321                 if ( $sum == 0 ) {
 322                         # No appropriate DB servers except maybe the master and some replica DBs with zero load
 323                         # Do NOT use the master
 324                         # Instead, this function will return false, triggering read-only mode,
 325                         # and a lagged replica DB will be used instead.
 326                         return false;
 327                 }
 328
 329                 if ( count( $loads ) == 0 ) {
 330                         return false;
 331                 }
 332
 333                 # Return a random representative of the remainder
 334                 return ArrayUtils::pickRandom( $loads );
 335         }
 336
 337         public function getReaderIndex( $group = false, $domain = false ) {
 338                 if ( count( $this->mServers ) == 1 ) {
 339                         // Skip the load balancing if there's only one server
 340                         return $this->getWriterIndex();
 341                 } elseif ( $group === false && $this->mReadIndex >= 0 ) {
 342                         // Shortcut if the generic reader index was already cached
 343                         return $this->mReadIndex;
 344                 }
 345
 346                 if ( $group !== false ) {
 347                         // Use the server weight array for this load group
 348                         if ( isset( $this->mGroupLoads[$group] ) ) {
 349                                 $loads = $this->mGroupLoads[$group];
 350                         } else {
 351                                 // No loads for this group, return false and the caller can use some other group
 352                                 $this->connLogger->info( __METHOD__ . ": no loads for group $group" );
 353
 354                                 return false;
 355                         }
 356                 } else {
 357                         // Use the generic load group
 358                         $loads = $this->mLoads;
 359                 }
 360
 361                 // Scale the configured load ratios according to each server's load and state
 362                 $this->getLoadMonitor()->scaleLoads( $loads, $domain );
 363
 364                 // Pick a server to use, accounting for weights, load, lag, and mWaitForPos
 365                 list( $i, $laggedReplicaMode ) = $this->pickReaderIndex( $loads, $domain );
 366                 if ( $i === false ) {
 367                         // Replica DB connection unsuccessful
 368                         return false;
 369                 }
 370
 371                 if ( $this->mWaitForPos && $i != $this->getWriterIndex() ) {
 372                         // Before any data queries are run, wait for the server to catch up to the
 373                         // specified position. This is used to improve session consistency. Note that
 374                         // when LoadBalancer::waitFor() sets mWaitForPos, the waiting triggers here,
 375                         // so update laggedReplicaMode as needed for consistency.
 376                         if ( !$this->doWait( $i ) ) {
 377                                 $laggedReplicaMode = true;
 378                         }
 379                 }
 380
 381                 if ( $this->mReadIndex <= 0 && $this->mLoads[$i] > 0 && $group === false ) {
 382                         // Cache the generic reader index for future ungrouped DB_REPLICA handles
 383                         $this->mReadIndex = $i;
 384                         // Record if the generic reader index is in "lagged replica DB" mode
 385                         if ( $laggedReplicaMode ) {
 386                                 $this->laggedReplicaMode = true;
 387                         }
 388                 }
 389
 390                 $serverName = $this->getServerName( $i );
 391                 $this->connLogger->debug( __METHOD__ . ": using server $serverName for group '$group'" );
 392
 393                 return $i;
 394         }
 395
 396         /**
 397          * @param array $loads List of server weights
 398          * @param string|bool $domain
 399          * @return array (reader index, lagged replica mode) or false on failure
 400          */
 401         private function pickReaderIndex( array $loads, $domain = false ) {
 402                 if ( !count( $loads ) ) {
 403                         throw new InvalidArgumentException( "Empty server array given to LoadBalancer" );
 404                 }
 405
 406                 /** @var int|bool $i Index of selected server */
 407                 $i = false;
 408                 /** @var bool $laggedReplicaMode Whether server is considered lagged */
 409                 $laggedReplicaMode = false;
 410
 411                 // Quickly look through the available servers for a server that meets criteria...
 412                 $currentLoads = $loads;
 413                 while ( count( $currentLoads ) ) {
 414                         if ( $this->mAllowLagged || $laggedReplicaMode ) {
 415                                 $i = ArrayUtils::pickRandom( $currentLoads );
 416                         } else {
 417                                 $i = false;
 418                                 if ( $this->mWaitForPos && $this->mWaitForPos->asOfTime() ) {
 419                                         // ChronologyProtecter sets mWaitForPos for session consistency.
 420                                         // This triggers doWait() after connect, so it's especially good to
 421                                         // avoid lagged servers so as to avoid excessive delay in that method.
 422                                         $ago = microtime( true ) - $this->mWaitForPos->asOfTime();
 423                                         // Aim for <= 1 second of waiting (being too picky can backfire)
 424                                         $i = $this->getRandomNonLagged( $currentLoads, $domain, $ago + 1 );
 425                                 }
 426                                 if ( $i === false ) {
 427                                         // Any server with less lag than it's 'max lag' param is preferable
 428                                         $i = $this->getRandomNonLagged( $currentLoads, $domain );
 429                                 }
 430                                 if ( $i === false && count( $currentLoads ) != 0 ) {
 431                                         // All replica DBs lagged. Switch to read-only mode
 432                                         $this->replLogger->error( "All replica DBs lagged. Switch to read-only mode" );
 433                                         $i = ArrayUtils::pickRandom( $currentLoads );
 434                                         $laggedReplicaMode = true;
 435                                 }
 436                         }
 437
 438                         if ( $i === false ) {
 439                                 // pickRandom() returned false.
 440                                 // This is permanent and means the configuration or the load monitor
 441                                 // wants us to return false.
 442                                 $this->connLogger->debug( __METHOD__ . ": pickRandom() returned false" );
 443
 444                                 return [ false, false ];
 445                         }
 446
 447                         $serverName = $this->getServerName( $i );
 448                         $this->connLogger->debug( __METHOD__ . ": Using reader #$i: $serverName..." );
 449
 450                         $conn = $this->openConnection( $i, $domain );
 451                         if ( !$conn ) {
 452                                 $this->connLogger->warning( __METHOD__ . ": Failed connecting to $i/$domain" );
 453                                 unset( $currentLoads[$i] ); // avoid this server next iteration
 454                                 $i = false;
 455                                 continue;
 456                         }
 457
 458                         // Decrement reference counter, we are finished with this connection.
 459                         // It will be incremented for the caller later.
 460                         if ( $domain !== false ) {
 461                                 $this->reuseConnection( $conn );
 462                         }
 463
 464                         // Return this server
 465                         break;
 466                 }
 467
 468                 // If all servers were down, quit now
 469                 if ( !count( $currentLoads ) ) {
 470                         $this->connLogger->error( "All servers down" );
 471                 }
 472
 473                 return [ $i, $laggedReplicaMode ];
 474         }
 475
 476         public function waitFor( $pos ) {
 477                 $oldPos = $this->mWaitForPos;
 478                 try {
 479                         $this->mWaitForPos = $pos;
 480                         // If a generic reader connection was already established, then wait now
 481                         $i = $this->mReadIndex;
 482                         if ( $i > 0 ) {
 483                                 if ( !$this->doWait( $i ) ) {
 484                                         $this->laggedReplicaMode = true;
 485                                 }
 486                         }
 487                 } finally {
 488                         // Restore the older position if it was higher since this is used for lag-protection
 489                         $this->setWaitForPositionIfHigher( $oldPos );
 490                 }
 491         }
 492
 493         public function waitForOne( $pos, $timeout = null ) {
 494                 $oldPos = $this->mWaitForPos;
 495                 try {
 496                         $this->mWaitForPos = $pos;
 497
 498                         $i = $this->mReadIndex;
 499                         if ( $i <= 0 ) {
 500                                 // Pick a generic replica DB if there isn't one yet
 501                                 $readLoads = $this->mLoads;
 502                                 unset( $readLoads[$this->getWriterIndex()] ); // replica DBs only
 503                                 $readLoads = array_filter( $readLoads ); // with non-zero load
 504                                 $i = ArrayUtils::pickRandom( $readLoads );
 505                         }
 506
 507                         if ( $i > 0 ) {
 508                                 $ok = $this->doWait( $i, true, $timeout );
 509                         } else {
 510                                 $ok = true; // no applicable loads
 511                         }
 512                 } finally {
 513                         # Restore the old position, as this is not used for lag-protection but for throttling
 514                         $this->mWaitForPos = $oldPos;
 515                 }
 516
 517                 return $ok;
 518         }
 519
 520         public function waitForAll( $pos, $timeout = null ) {
 521                 $oldPos = $this->mWaitForPos;
 522                 try {
 523                         $this->mWaitForPos = $pos;
 524                         $serverCount = count( $this->mServers );
 525
 526                         $ok = true;
 527                         for ( $i = 1; $i < $serverCount; $i++ ) {
 528                                 if ( $this->mLoads[$i] > 0 ) {
 529                                         $ok = $this->doWait( $i, true, $timeout ) && $ok;
 530                                 }
 531                         }
 532                 } finally {
 533                         # Restore the old position, as this is not used for lag-protection but for throttling
 534                         $this->mWaitForPos = $oldPos;
 535                 }
 536
 537                 return $ok;
 538         }
 539
 540         /**
 541          * @param DBMasterPos|bool $pos
 542          */
 543         private function setWaitForPositionIfHigher( $pos ) {
 544                 if ( !$pos ) {
 545                         return;
 546                 }
 547
 548                 if ( !$this->mWaitForPos || $pos->hasReached( $this->mWaitForPos ) ) {
 549                         $this->mWaitForPos = $pos;
 550                 }
 551         }
 552
 553         /**
 554          * @param int $i
 555          * @return IDatabase|bool
 556          */
 557         public function getAnyOpenConnection( $i ) {
 558                 foreach ( $this->mConns as $connsByServer ) {
 559                         if ( !empty( $connsByServer[$i] ) ) {
 560                                 /** @var IDatabase[] $serverConns */
 561                                 $serverConns = $connsByServer[$i];
 562
 563                                 return reset( $serverConns );
 564                         }
 565                 }
 566
 567                 return false;
 568         }
 569
 570         /**
 571          * Wait for a given replica DB to catch up to the master pos stored in $this
 572          * @param int $index Server index
 573          * @param bool $open Check the server even if a new connection has to be made
 574          * @param int $timeout Max seconds to wait; default is mWaitTimeout
 575          * @return bool
 576          */
 577         protected function doWait( $index, $open = false, $timeout = null ) {
 578                 $close = false; // close the connection afterwards
 579
 580                 // Check if we already know that the DB has reached this point
 581                 $server = $this->getServerName( $index );
 582                 $key = $this->srvCache->makeGlobalKey( __CLASS__, 'last-known-pos', $server, 'v1' );
 583                 /** @var DBMasterPos $knownReachedPos */
 584                 $knownReachedPos = $this->srvCache->get( $key );
 585                 if (
 586                         $knownReachedPos instanceof DBMasterPos &&
 587                         $knownReachedPos->hasReached( $this->mWaitForPos )
 588                 ) {
 589                         $this->replLogger->debug( __METHOD__ .
 590                                 ': replica DB {dbserver} known to be caught up (pos >= $knownReachedPos).',
 591                                 [ 'dbserver' => $server ] );
 592                         return true;
 593                 }
 594
 595                 // Find a connection to wait on, creating one if needed and allowed
 596                 $conn = $this->getAnyOpenConnection( $index );
 597                 if ( !$conn ) {
 598                         if ( !$open ) {
 599                                 $this->replLogger->debug( __METHOD__ . ': no connection open for {dbserver}',
 600                                         [ 'dbserver' => $server ] );
 601
 602                                 return false;
 603                         } else {
 604                                 $conn = $this->openConnection( $index, self::DOMAIN_ANY );
 605                                 if ( !$conn ) {
 606                                         $this->replLogger->warning( __METHOD__ . ': failed to connect to {dbserver}',
 607                                                 [ 'dbserver' => $server ] );
 608
 609                                         return false;
 610                                 }
 611                                 // Avoid connection spam in waitForAll() when connections
 612                                 // are made just for the sake of doing this lag check.
 613                                 $close = true;
 614                         }
 615                 }
 616
 617                 $this->replLogger->info( __METHOD__ . ': Waiting for replica DB {dbserver} to catch up...',
 618                         [ 'dbserver' => $server ] );
 619                 $timeout = $timeout ?: $this->mWaitTimeout;
 620                 $result = $conn->masterPosWait( $this->mWaitForPos, $timeout );
 621
 622                 if ( $result == -1 || is_null( $result ) ) {
 623                         // Timed out waiting for replica DB, use master instead
 624                         $this->replLogger->warning(
 625                                 __METHOD__ . ': Timed out waiting on {host} pos {pos}',
 626                                 [ 'host' => $server, 'pos' => $this->mWaitForPos ]
 627                         );
 628                         $ok = false;
 629                 } else {
 630                         $this->replLogger->info( __METHOD__ . ": Done" );
 631                         $ok = true;
 632                         // Remember that the DB reached this point
 633                         $this->srvCache->set( $key, $this->mWaitForPos, BagOStuff::TTL_DAY );
 634                 }
 635
 636                 if ( $close ) {
 637                         $this->closeConnection( $conn );
 638                 }
 639
 640                 return $ok;
 641         }
 642
 643         public function getConnection( $i, $groups = [], $domain = false, $flags = 0 ) {
 644                 if ( $i === null || $i === false ) {
 645                         throw new InvalidArgumentException( 'Attempt to call ' . __METHOD__ .
 646                                 ' with invalid server index' );
 647                 }
 648
 649                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 650                         $domain = false; // local connection requested
 651                 }
 652
 653                 $groups = ( $groups === false || $groups === [] )
 654                         ? [ false ] // check one "group": the generic pool
 655                         : (array)$groups;
 656
 657                 $masterOnly = ( $i == self::DB_MASTER || $i == $this->getWriterIndex() );
 658                 $oldConnsOpened = $this->connsOpened; // connections open now
 659
 660                 if ( $i == self::DB_MASTER ) {
 661                         $i = $this->getWriterIndex();
 662                 } else {
 663                         # Try to find an available server in any the query groups (in order)
 664                         foreach ( $groups as $group ) {
 665                                 $groupIndex = $this->getReaderIndex( $group, $domain );
 666                                 if ( $groupIndex !== false ) {
 667                                         $i = $groupIndex;
 668                                         break;
 669                                 }
 670                         }
 671                 }
 672
 673                 # Operation-based index
 674                 if ( $i == self::DB_REPLICA ) {
 675                         $this->mLastError = 'Unknown error'; // reset error string
 676                         # Try the general server pool if $groups are unavailable.
 677                         $i = ( $groups === [ false ] )
 678                                 ? false // don't bother with this if that is what was tried above
 679                                 : $this->getReaderIndex( false, $domain );
 680                         # Couldn't find a working server in getReaderIndex()?
 681                         if ( $i === false ) {
 682                                 $this->mLastError = 'No working replica DB server: ' . $this->mLastError;
 683                                 // Throw an exception
 684                                 $this->reportConnectionError();
 685                                 return null; // not reached
 686                         }
 687                 }
 688
 689                 # Now we have an explicit index into the servers array
 690                 $conn = $this->openConnection( $i, $domain, $flags );
 691                 if ( !$conn ) {
 692                         // Throw an exception
 693                         $this->reportConnectionError();
 694                         return null; // not reached
 695                 }
 696
 697                 # Profile any new connections that happen
 698                 if ( $this->connsOpened > $oldConnsOpened ) {
 699                         $host = $conn->getServer();
 700                         $dbname = $conn->getDBname();
 701                         $this->trxProfiler->recordConnection( $host, $dbname, $masterOnly );
 702                 }
 703
 704                 if ( $masterOnly ) {
 705                         # Make master-requested DB handles inherit any read-only mode setting
 706                         $conn->setLBInfo( 'readOnlyReason', $this->getReadOnlyReason( $domain, $conn ) );
 707                 }
 708
 709                 return $conn;
 710         }
 711
 712         public function reuseConnection( $conn ) {
 713                 $serverIndex = $conn->getLBInfo( 'serverIndex' );
 714                 $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 715                 if ( $serverIndex === null || $refCount === null ) {
 716                         /**
 717                          * This can happen in code like:
 718                          *   foreach ( $dbs as $db ) {
 719                          *     $conn = $lb->getConnection( $lb::DB_REPLICA, [], $db );
 720                          *     ...
 721                          *     $lb->reuseConnection( $conn );
 722                          *   }
 723                          * When a connection to the local DB is opened in this way, reuseConnection()
 724                          * should be ignored
 725                          */
 726                         return;
 727                 } elseif ( $conn instanceof DBConnRef ) {
 728                         // DBConnRef already handles calling reuseConnection() and only passes the live
 729                         // Database instance to this method. Any caller passing in a DBConnRef is broken.
 730                         $this->connLogger->error( __METHOD__ . ": got DBConnRef instance.\n" .
 731                                 ( new RuntimeException() )->getTraceAsString() );
 732
 733                         return;
 734                 }
 735
 736                 if ( $this->disabled ) {
 737                         return; // DBConnRef handle probably survived longer than the LoadBalancer
 738                 }
 739
 740                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
 741                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 742                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 743                 } else {
 744                         $connFreeKey = self::KEY_FOREIGN_FREE;
 745                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 746                 }
 747
 748                 $domain = $conn->getDomainID();
 749                 if ( !isset( $this->mConns[$connInUseKey][$serverIndex][$domain] ) ) {
 750                         throw new InvalidArgumentException( __METHOD__ .
 751                                 ": connection $serverIndex/$domain not found; it may have already been freed." );
 752                 } elseif ( $this->mConns[$connInUseKey][$serverIndex][$domain] !== $conn ) {
 753                         throw new InvalidArgumentException( __METHOD__ .
 754                                 ": connection $serverIndex/$domain mismatched; it may have already been freed." );
 755                 }
 756
 757                 $conn->setLBInfo( 'foreignPoolRefCount', --$refCount );
 758                 if ( $refCount <= 0 ) {
 759                         $this->mConns[$connFreeKey][$serverIndex][$domain] = $conn;
 760                         unset( $this->mConns[$connInUseKey][$serverIndex][$domain] );
 761                         if ( !$this->mConns[$connInUseKey][$serverIndex] ) {
 762                                 unset( $this->mConns[$connInUseKey][$serverIndex] ); // clean up
 763                         }
 764                         $this->connLogger->debug( __METHOD__ . ": freed connection $serverIndex/$domain" );
 765                 } else {
 766                         $this->connLogger->debug( __METHOD__ .
 767                                 ": reference count for $serverIndex/$domain reduced to $refCount" );
 768                 }
 769         }
 770
 771         public function getConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 772                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 773
 774                 return new DBConnRef( $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 775         }
 776
 777         public function getLazyConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 778                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 779
 780                 return new DBConnRef( $this, [ $db, $groups, $domain, $flags ] );
 781         }
 782
 783         public function getMaintenanceConnectionRef( $db, $groups = [], $domain = false, $flags = 0 ) {
 784                 $domain = ( $domain !== false ) ? $domain : $this->localDomain;
 785
 786                 return new MaintainableDBConnRef(
 787                         $this, $this->getConnection( $db, $groups, $domain, $flags ) );
 788         }
 789
 790         public function openConnection( $i, $domain = false, $flags = 0 ) {
 791                 if ( $this->localDomain->equals( $domain ) || $domain === $this->localDomainIdAlias ) {
 792                         $domain = false; // local connection requested
 793                 }
 794
 795                 if ( !$this->chronProtInitialized && $this->chronProt ) {
 796                         $this->connLogger->debug( __METHOD__ . ': calling initLB() before first connection.' );
 797                         // Load CP positions before connecting so that doWait() triggers later if needed
 798                         $this->chronProtInitialized = true;
 799                         $this->chronProt->initLB( $this );
 800                 }
 801
 802                 // Check if an auto-commit connection is being requested. If so, it will not reuse the
 803                 // main set of DB connections but rather its own pool since:
 804                 // a) those are usually set to implicitly use transaction rounds via DBO_TRX
 805                 // b) those must support the use of explicit transaction rounds via beginMasterChanges()
 806                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTO ) == self::CONN_TRX_AUTO );
 807
 808                 if ( $domain !== false ) {
 809                         // Connection is to a foreign domain
 810                         $conn = $this->openForeignConnection( $i, $domain, $flags );
 811                 } else {
 812                         // Connection is to the local domain
 813                         $connKey = $autoCommit ? self::KEY_LOCAL_NOROUND : self::KEY_LOCAL;
 814                         if ( isset( $this->mConns[$connKey][$i][0] ) ) {
 815                                 $conn = $this->mConns[$connKey][$i][0];
 816                         } else {
 817                                 if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 818                                         throw new InvalidArgumentException( "No server with index '$i'." );
 819                                 }
 820                                 // Open a new connection
 821                                 $server = $this->mServers[$i];
 822                                 $server['serverIndex'] = $i;
 823                                 $server['autoCommitOnly'] = $autoCommit;
 824                                 $conn = $this->reallyOpenConnection( $server, false );
 825                                 $host = $this->getServerName( $i );
 826                                 if ( $conn->isOpen() ) {
 827                                         $this->connLogger->debug( "Connected to database $i at '$host'." );
 828                                         $this->mConns[$connKey][$i][0] = $conn;
 829                                 } else {
 830                                         $this->connLogger->warning( "Failed to connect to database $i at '$host'." );
 831                                         $this->errorConnection = $conn;
 832                                         $conn = false;
 833                                 }
 834                         }
 835                 }
 836
 837                 if ( $conn instanceof IDatabase && !$conn->isOpen() ) {
 838                         // Connection was made but later unrecoverably lost for some reason.
 839                         // Do not return a handle that will just throw exceptions on use,
 840                         // but let the calling code (e.g. getReaderIndex) try another server.
 841                         // See DatabaseMyslBase::ping() for how this can happen.
 842                         $this->errorConnection = $conn;
 843                         $conn = false;
 844                 }
 845
 846                 if ( $autoCommit && $conn instanceof IDatabase ) {
 847                         $conn->clearFlag( $conn::DBO_TRX ); // auto-commit mode
 848                 }
 849
 850                 return $conn;
 851         }
 852
 853         /**
 854          * Open a connection to a foreign DB, or return one if it is already open.
 855          *
 856          * Increments a reference count on the returned connection which locks the
 857          * connection to the requested domain. This reference count can be
 858          * decremented by calling reuseConnection().
 859          *
 860          * If a connection is open to the appropriate server already, but with the wrong
 861          * database, it will be switched to the right database and returned, as long as
 862          * it has been freed first with reuseConnection().
 863          *
 864          * On error, returns false, and the connection which caused the
 865          * error will be available via $this->errorConnection.
 866          *
 867          * @note If disable() was called on this LoadBalancer, this method will throw a DBAccessError.
 868          *
 869          * @param int $i Server index
 870          * @param string $domain Domain ID to open
 871          * @param int $flags Class CONN_* constant bitfield
 872          * @return Database
 873          */
 874         private function openForeignConnection( $i, $domain, $flags = 0 ) {
 875                 $domainInstance = DatabaseDomain::newFromId( $domain );
 876                 $dbName = $domainInstance->getDatabase();
 877                 $prefix = $domainInstance->getTablePrefix();
 878                 $autoCommit = ( ( $flags & self::CONN_TRX_AUTO ) == self::CONN_TRX_AUTO );
 879
 880                 if ( $autoCommit ) {
 881                         $connFreeKey = self::KEY_FOREIGN_FREE_NOROUND;
 882                         $connInUseKey = self::KEY_FOREIGN_INUSE_NOROUND;
 883                 } else {
 884                         $connFreeKey = self::KEY_FOREIGN_FREE;
 885                         $connInUseKey = self::KEY_FOREIGN_INUSE;
 886                 }
 887
 888                 if ( isset( $this->mConns[$connInUseKey][$i][$domain] ) ) {
 889                         // Reuse an in-use connection for the same domain
 890                         $conn = $this->mConns[$connInUseKey][$i][$domain];
 891                         $this->connLogger->debug( __METHOD__ . ": reusing connection $i/$domain" );
 892                 } elseif ( isset( $this->mConns[$connFreeKey][$i][$domain] ) ) {
 893                         // Reuse a free connection for the same domain
 894                         $conn = $this->mConns[$connFreeKey][$i][$domain];
 895                         unset( $this->mConns[$connFreeKey][$i][$domain] );
 896                         $this->mConns[$connInUseKey][$i][$domain] = $conn;
 897                         $this->connLogger->debug( __METHOD__ . ": reusing free connection $i/$domain" );
 898                 } elseif ( !empty( $this->mConns[$connFreeKey][$i] ) ) {
 899                         // Reuse a free connection from another domain
 900                         $conn = reset( $this->mConns[$connFreeKey][$i] );
 901                         $oldDomain = key( $this->mConns[$connFreeKey][$i] );
 902                         // The empty string as a DB name means "don't care".
 903                         // DatabaseMysqlBase::open() already handle this on connection.
 904                         if ( strlen( $dbName ) && !$conn->selectDB( $dbName ) ) {
 905                                 $this->mLastError = "Error selecting database '$dbName' on server " .
 906                                         $conn->getServer() . " from client host {$this->host}";
 907                                 $this->errorConnection = $conn;
 908                                 $conn = false;
 909                         } else {
 910                                 $conn->tablePrefix( $prefix );
 911                                 unset( $this->mConns[$connFreeKey][$i][$oldDomain] );
 912                                 $this->mConns[$connInUseKey][$i][$domain] = $conn;
 913                                 $this->connLogger->debug( __METHOD__ .
 914                                         ": reusing free connection from $oldDomain for $domain" );
 915                         }
 916                 } else {
 917                         if ( !isset( $this->mServers[$i] ) || !is_array( $this->mServers[$i] ) ) {
 918                                 throw new InvalidArgumentException( "No server with index '$i'." );
 919                         }
 920                         // Open a new connection
 921                         $server = $this->mServers[$i];
 922                         $server['serverIndex'] = $i;
 923                         $server['foreignPoolRefCount'] = 0;
 924                         $server['foreign'] = true;
 925                         $server['autoCommitOnly'] = $autoCommit;
 926                         $conn = $this->reallyOpenConnection( $server, $dbName );
 927                         if ( !$conn->isOpen() ) {
 928                                 $this->connLogger->warning( __METHOD__ . ": connection error for $i/$domain" );
 929                                 $this->errorConnection = $conn;
 930                                 $conn = false;
 931                         } else {
 932                                 $conn->tablePrefix( $prefix );
 933                                 $this->mConns[$connInUseKey][$i][$domain] = $conn;
 934                                 $this->connLogger->debug( __METHOD__ . ": opened new connection for $i/$domain" );
 935                         }
 936                 }
 937
 938                 // Increment reference count
 939                 if ( $conn instanceof IDatabase ) {
 940                         $refCount = $conn->getLBInfo( 'foreignPoolRefCount' );
 941                         $conn->setLBInfo( 'foreignPoolRefCount', $refCount + 1 );
 942                 }
 943
 944                 return $conn;
 945         }
 946
 947         /**
 948          * Test if the specified index represents an open connection
 949          *
 950          * @param int $index Server index
 951          * @access private
 952          * @return bool
 953          */
 954         private function isOpen( $index ) {
 955                 if ( !is_int( $index ) ) {
 956                         return false;
 957                 }
 958
 959                 return (bool)$this->getAnyOpenConnection( $index );
 960         }
 961
 962         /**
 963          * Really opens a connection. Uncached.
 964          * Returns a Database object whether or not the connection was successful.
 965          * @access private
 966          *
 967          * @param array $server
 968          * @param string|bool $dbNameOverride Use "" to not select any database
 969          * @return Database
 970          * @throws DBAccessError
 971          * @throws InvalidArgumentException
 972          */
 973         protected function reallyOpenConnection( array $server, $dbNameOverride = false ) {
 974                 if ( $this->disabled ) {
 975                         throw new DBAccessError();
 976                 }
 977
 978                 if ( $dbNameOverride !== false ) {
 979                         $server['dbname'] = $dbNameOverride;
 980                 }
 981
 982                 // Let the handle know what the cluster master is (e.g. "db1052")
 983                 $masterName = $this->getServerName( $this->getWriterIndex() );
 984                 $server['clusterMasterHost'] = $masterName;
 985
 986                 // Log when many connection are made on requests
 987                 if ( ++$this->connsOpened >= self::CONN_HELD_WARN_THRESHOLD ) {
 988                         $this->perfLogger->warning( __METHOD__ . ": " .
 989                                 "{$this->connsOpened}+ connections made (master=$masterName)" );
 990                 }
 991
 992                 $server['srvCache'] = $this->srvCache;
 993                 // Set loggers and profilers
 994                 $server['connLogger'] = $this->connLogger;
 995                 $server['queryLogger'] = $this->queryLogger;
 996                 $server['errorLogger'] = $this->errorLogger;
 997                 $server['profiler'] = $this->profiler;
 998                 $server['trxProfiler'] = $this->trxProfiler;
 999                 // Use the same agent and PHP mode for all DB handles
1000                 $server['cliMode'] = $this->cliMode;
1001                 $server['agent'] = $this->agent;
1002                 // Use DBO_DEFAULT flags by default for LoadBalancer managed databases. Assume that the
1003                 // application calls LoadBalancer::commitMasterChanges() before the PHP script completes.
1004                 $server['flags'] = isset( $server['flags'] ) ? $server['flags'] : IDatabase::DBO_DEFAULT;
1005
1006                 // Create a live connection object
1007                 try {
1008                         $db = Database::factory( $server['type'], $server );
1009                 } catch ( DBConnectionError $e ) {
1010                         // FIXME: This is probably the ugliest thing I have ever done to
1011                         // PHP. I'm half-expecting it to segfault, just out of disgust. -- TS
1012                         $db = $e->db;
1013                 }
1014
1015                 $db->setLBInfo( $server );
1016                 $db->setLazyMasterHandle(
1017                         $this->getLazyConnectionRef( self::DB_MASTER, [], $db->getDomainID() )
1018                 );
1019                 $db->setTableAliases( $this->tableAliases );
1020
1021                 if ( $server['serverIndex'] === $this->getWriterIndex() ) {
1022                         if ( $this->trxRoundId !== false ) {
1023                                 $this->applyTransactionRoundFlags( $db );
1024                         }
1025                         foreach ( $this->trxRecurringCallbacks as $name => $callback ) {
1026                                 $db->setTransactionListener( $name, $callback );
1027                         }
1028                 }
1029
1030                 return $db;
1031         }
1032
1033         /**
1034          * @throws DBConnectionError
1035          */
1036         private function reportConnectionError() {
1037                 $conn = $this->errorConnection; // the connection which caused the error
1038                 $context = [
1039                         'method' => __METHOD__,
1040                         'last_error' => $this->mLastError,
1041                 ];
1042
1043                 if ( $conn instanceof IDatabase ) {
1044                         $context['db_server'] = $conn->getServer();
1045                         $this->connLogger->warning(
1046                                 "Connection error: {last_error} ({db_server})",
1047                                 $context
1048                         );
1049
1050                         // throws DBConnectionError
1051                         $conn->reportConnectionError( "{$this->mLastError} ({$context['db_server']})" );
1052                 } else {
1053                         // No last connection, probably due to all servers being too busy
1054                         $this->connLogger->error(
1055                                 "LB failure with no last connection. Connection error: {last_error}",
1056                                 $context
1057                         );
1058
1059                         // If all servers were busy, mLastError will contain something sensible
1060                         throw new DBConnectionError( null, $this->mLastError );
1061                 }
1062         }
1063
1064         public function getWriterIndex() {
1065                 return 0;
1066         }
1067
1068         public function haveIndex( $i ) {
1069                 return array_key_exists( $i, $this->mServers );
1070         }
1071
1072         public function isNonZeroLoad( $i ) {
1073                 return array_key_exists( $i, $this->mServers ) && $this->mLoads[$i] != 0;
1074         }
1075
1076         public function getServerCount() {
1077                 return count( $this->mServers );
1078         }
1079
1080         public function getServerName( $i ) {
1081                 if ( isset( $this->mServers[$i]['hostName'] ) ) {
1082                         $name = $this->mServers[$i]['hostName'];
1083                 } elseif ( isset( $this->mServers[$i]['host'] ) ) {
1084                         $name = $this->mServers[$i]['host'];
1085                 } else {
1086                         $name = '';
1087                 }
1088
1089                 return ( $name != '' ) ? $name : 'localhost';
1090         }
1091
1092         public function getServerType( $i ) {
1093                 return isset( $this->mServers[$i]['type'] ) ? $this->mServers[$i]['type'] : 'unknown';
1094         }
1095
1096         public function getMasterPos() {
1097                 # If this entire request was served from a replica DB without opening a connection to the
1098                 # master (however unlikely that may be), then we can fetch the position from the replica DB.
1099                 $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1100                 if ( !$masterConn ) {
1101                         $serverCount = count( $this->mServers );
1102                         for ( $i = 1; $i < $serverCount; $i++ ) {
1103                                 $conn = $this->getAnyOpenConnection( $i );
1104                                 if ( $conn ) {
1105                                         return $conn->getReplicaPos();
1106                                 }
1107                         }
1108                 } else {
1109                         return $masterConn->getMasterPos();
1110                 }
1111
1112                 return false;
1113         }
1114
1115         public function disable() {
1116                 $this->closeAll();
1117                 $this->disabled = true;
1118         }
1119
1120         public function closeAll() {
1121                 $this->forEachOpenConnection( function ( IDatabase $conn ) {
1122                         $host = $conn->getServer();
1123                         $this->connLogger->debug( "Closing connection to database '$host'." );
1124                         $conn->close();
1125                 } );
1126
1127                 $this->mConns = [
1128                         self::KEY_LOCAL => [],
1129                         self::KEY_FOREIGN_INUSE => [],
1130                         self::KEY_FOREIGN_FREE => [],
1131                         self::KEY_LOCAL_NOROUND => [],
1132                         self::KEY_FOREIGN_INUSE_NOROUND => [],
1133                         self::KEY_FOREIGN_FREE_NOROUND => []
1134                 ];
1135                 $this->connsOpened = 0;
1136         }
1137
1138         public function closeConnection( IDatabase $conn ) {
1139                 $serverIndex = $conn->getLBInfo( 'serverIndex' ); // second index level of mConns
1140                 foreach ( $this->mConns as $type => $connsByServer ) {
1141                         if ( !isset( $connsByServer[$serverIndex] ) ) {
1142                                 continue;
1143                         }
1144
1145                         foreach ( $connsByServer[$serverIndex] as $i => $trackedConn ) {
1146                                 if ( $conn === $trackedConn ) {
1147                                         $host = $this->getServerName( $i );
1148                                         $this->connLogger->debug( "Closing connection to database $i at '$host'." );
1149                                         unset( $this->mConns[$type][$serverIndex][$i] );
1150                                         --$this->connsOpened;
1151                                         break 2;
1152                                 }
1153                         }
1154                 }
1155
1156                 $conn->close();
1157         }
1158
1159         public function commitAll( $fname = __METHOD__ ) {
1160                 $failures = [];
1161
1162                 $restore = ( $this->trxRoundId !== false );
1163                 $this->trxRoundId = false;
1164                 $this->forEachOpenConnection(
1165                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1166                                 try {
1167                                         $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1168                                 } catch ( DBError $e ) {
1169                                         call_user_func( $this->errorLogger, $e );
1170                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1171                                 }
1172                                 if ( $restore && $conn->getLBInfo( 'master' ) ) {
1173                                         $this->undoTransactionRoundFlags( $conn );
1174                                 }
1175                         }
1176                 );
1177
1178                 if ( $failures ) {
1179                         throw new DBExpectedError(
1180                                 null,
1181                                 "Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1182                         );
1183                 }
1184         }
1185
1186         public function finalizeMasterChanges() {
1187                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1188                         // Any error should cause all DB transactions to be rolled back together
1189                         $conn->setTrxEndCallbackSuppression( false );
1190                         $conn->runOnTransactionPreCommitCallbacks();
1191                         // Defer post-commit callbacks until COMMIT finishes for all DBs
1192                         $conn->setTrxEndCallbackSuppression( true );
1193                 } );
1194         }
1195
1196         public function approveMasterChanges( array $options ) {
1197                 $limit = isset( $options['maxWriteDuration'] ) ? $options['maxWriteDuration'] : 0;
1198                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( $limit ) {
1199                         // If atomic sections or explicit transactions are still open, some caller must have
1200                         // caught an exception but failed to properly rollback any changes. Detect that and
1201                         // throw and error (causing rollback).
1202                         if ( $conn->explicitTrxActive() ) {
1203                                 throw new DBTransactionError(
1204                                         $conn,
1205                                         "Explicit transaction still active. A caller may have caught an error."
1206                                 );
1207                         }
1208                         // Assert that the time to replicate the transaction will be sane.
1209                         // If this fails, then all DB transactions will be rollback back together.
1210                         $time = $conn->pendingWriteQueryDuration( $conn::ESTIMATE_DB_APPLY );
1211                         if ( $limit > 0 && $time > $limit ) {
1212                                 throw new DBTransactionSizeError(
1213                                         $conn,
1214                                         "Transaction spent $time second(s) in writes, exceeding the limit of $limit.",
1215                                         [ $time, $limit ]
1216                                 );
1217                         }
1218                         // If a connection sits idle while slow queries execute on another, that connection
1219                         // may end up dropped before the commit round is reached. Ping servers to detect this.
1220                         if ( $conn->writesOrCallbacksPending() && !$conn->ping() ) {
1221                                 throw new DBTransactionError(
1222                                         $conn,
1223                                         "A connection to the {$conn->getDBname()} database was lost before commit."
1224                                 );
1225                         }
1226                 } );
1227         }
1228
1229         public function beginMasterChanges( $fname = __METHOD__ ) {
1230                 if ( $this->trxRoundId !== false ) {
1231                         throw new DBTransactionError(
1232                                 null,
1233                                 "$fname: Transaction round '{$this->trxRoundId}' already started."
1234                         );
1235                 }
1236                 $this->trxRoundId = $fname;
1237
1238                 $failures = [];
1239                 $this->forEachOpenMasterConnection(
1240                         function ( Database $conn ) use ( $fname, &$failures ) {
1241                                 $conn->setTrxEndCallbackSuppression( true );
1242                                 try {
1243                                         $conn->flushSnapshot( $fname );
1244                                 } catch ( DBError $e ) {
1245                                         call_user_func( $this->errorLogger, $e );
1246                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1247                                 }
1248                                 $conn->setTrxEndCallbackSuppression( false );
1249                                 $this->applyTransactionRoundFlags( $conn );
1250                         }
1251                 );
1252
1253                 if ( $failures ) {
1254                         throw new DBExpectedError(
1255                                 null,
1256                                 "$fname: Flush failed on server(s) " . implode( "\n", array_unique( $failures ) )
1257                         );
1258                 }
1259         }
1260
1261         public function commitMasterChanges( $fname = __METHOD__ ) {
1262                 $failures = [];
1263
1264                 /** @noinspection PhpUnusedLocalVariableInspection */
1265                 $scope = $this->getScopedPHPBehaviorForCommit(); // try to ignore client aborts
1266
1267                 $restore = ( $this->trxRoundId !== false );
1268                 $this->trxRoundId = false;
1269                 $this->forEachOpenMasterConnection(
1270                         function ( IDatabase $conn ) use ( $fname, $restore, &$failures ) {
1271                                 try {
1272                                         if ( $conn->writesOrCallbacksPending() ) {
1273                                                 $conn->commit( $fname, $conn::FLUSHING_ALL_PEERS );
1274                                         } elseif ( $restore ) {
1275                                                 $conn->flushSnapshot( $fname );
1276                                         }
1277                                 } catch ( DBError $e ) {
1278                                         call_user_func( $this->errorLogger, $e );
1279                                         $failures[] = "{$conn->getServer()}: {$e->getMessage()}";
1280                                 }
1281                                 if ( $restore ) {
1282                                         $this->undoTransactionRoundFlags( $conn );
1283                                 }
1284                         }
1285                 );
1286
1287                 if ( $failures ) {
1288                         throw new DBExpectedError(
1289                                 null,
1290                                 "$fname: Commit failed on server(s) " . implode( "\n", array_unique( $failures ) )
1291                         );
1292                 }
1293         }
1294
1295         public function runMasterPostTrxCallbacks( $type ) {
1296                 $e = null; // first exception
1297                 $this->forEachOpenMasterConnection( function ( Database $conn ) use ( $type, &$e ) {
1298                         $conn->setTrxEndCallbackSuppression( false );
1299                         if ( $conn->writesOrCallbacksPending() ) {
1300                                 // This happens if onTransactionIdle() callbacks leave callbacks on *another* DB
1301                                 // (which finished its callbacks already). Warn and recover in this case. Let the
1302                                 // callbacks run in the final commitMasterChanges() in LBFactory::shutdown().
1303                                 $this->queryLogger->info( __METHOD__ . ": found writes/callbacks pending." );
1304                                 return;
1305                         } elseif ( $conn->trxLevel() ) {
1306                                 // This happens for single-DB setups where DB_REPLICA uses the master DB,
1307                                 // thus leaving an implicit read-only transaction open at this point. It
1308                                 // also happens if onTransactionIdle() callbacks leave implicit transactions
1309                                 // open on *other* DBs (which is slightly improper). Let these COMMIT on the
1310                                 // next call to commitMasterChanges(), possibly in LBFactory::shutdown().
1311                                 return;
1312                         }
1313                         try {
1314                                 $conn->runOnTransactionIdleCallbacks( $type );
1315                         } catch ( Exception $ex ) {
1316                                 $e = $e ?: $ex;
1317                         }
1318                         try {
1319                                 $conn->runTransactionListenerCallbacks( $type );
1320                         } catch ( Exception $ex ) {
1321                                 $e = $e ?: $ex;
1322                         }
1323                 } );
1324
1325                 return $e;
1326         }
1327
1328         public function rollbackMasterChanges( $fname = __METHOD__ ) {
1329                 $restore = ( $this->trxRoundId !== false );
1330                 $this->trxRoundId = false;
1331                 $this->forEachOpenMasterConnection(
1332                         function ( IDatabase $conn ) use ( $fname, $restore ) {
1333                                 if ( $conn->writesOrCallbacksPending() ) {
1334                                         $conn->rollback( $fname, $conn::FLUSHING_ALL_PEERS );
1335                                 }
1336                                 if ( $restore ) {
1337                                         $this->undoTransactionRoundFlags( $conn );
1338                                 }
1339                         }
1340                 );
1341         }
1342
1343         public function suppressTransactionEndCallbacks() {
1344                 $this->forEachOpenMasterConnection( function ( Database $conn ) {
1345                         $conn->setTrxEndCallbackSuppression( true );
1346                 } );
1347         }
1348
1349         /**
1350          * @param IDatabase $conn
1351          */
1352         private function applyTransactionRoundFlags( IDatabase $conn ) {
1353                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1354                         return; // transaction rounds do not apply to these connections
1355                 }
1356
1357                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1358                         // DBO_TRX is controlled entirely by CLI mode presence with DBO_DEFAULT.
1359                         // Force DBO_TRX even in CLI mode since a commit round is expected soon.
1360                         $conn->setFlag( $conn::DBO_TRX, $conn::REMEMBER_PRIOR );
1361                         // If config has explicitly requested DBO_TRX be either on or off by not
1362                         // setting DBO_DEFAULT, then respect that. Forcing no transactions is useful
1363                         // for things like blob stores (ExternalStore) which want auto-commit mode.
1364                 }
1365         }
1366
1367         /**
1368          * @param IDatabase $conn
1369          */
1370         private function undoTransactionRoundFlags( IDatabase $conn ) {
1371                 if ( $conn->getLBInfo( 'autoCommitOnly' ) ) {
1372                         return; // transaction rounds do not apply to these connections
1373                 }
1374
1375                 if ( $conn->getFlag( $conn::DBO_DEFAULT ) ) {
1376                         $conn->restoreFlags( $conn::RESTORE_PRIOR );
1377                 }
1378         }
1379
1380         public function flushReplicaSnapshots( $fname = __METHOD__ ) {
1381                 $this->forEachOpenReplicaConnection( function ( IDatabase $conn ) {
1382                         $conn->flushSnapshot( __METHOD__ );
1383                 } );
1384         }
1385
1386         public function hasMasterConnection() {
1387                 return $this->isOpen( $this->getWriterIndex() );
1388         }
1389
1390         public function hasMasterChanges() {
1391                 $pending = 0;
1392                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$pending ) {
1393                         $pending |= $conn->writesOrCallbacksPending();
1394                 } );
1395
1396                 return (bool)$pending;
1397         }
1398
1399         public function lastMasterChangeTimestamp() {
1400                 $lastTime = false;
1401                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$lastTime ) {
1402                         $lastTime = max( $lastTime, $conn->lastDoneWrites() );
1403                 } );
1404
1405                 return $lastTime;
1406         }
1407
1408         public function hasOrMadeRecentMasterChanges( $age = null ) {
1409                 $age = ( $age === null ) ? $this->mWaitTimeout : $age;
1410
1411                 return ( $this->hasMasterChanges()
1412                         || $this->lastMasterChangeTimestamp() > microtime( true ) - $age );
1413         }
1414
1415         public function pendingMasterChangeCallers() {
1416                 $fnames = [];
1417                 $this->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$fnames ) {
1418                         $fnames = array_merge( $fnames, $conn->pendingWriteCallers() );
1419                 } );
1420
1421                 return $fnames;
1422         }
1423
1424         public function getLaggedReplicaMode( $domain = false ) {
1425                 // No-op if there is only one DB (also avoids recursion)
1426                 if ( !$this->laggedReplicaMode && $this->getServerCount() > 1 ) {
1427                         try {
1428                                 // See if laggedReplicaMode gets set
1429                                 $conn = $this->getConnection( self::DB_REPLICA, false, $domain );
1430                                 $this->reuseConnection( $conn );
1431                         } catch ( DBConnectionError $e ) {
1432                                 // Avoid expensive re-connect attempts and failures
1433                                 $this->allReplicasDownMode = true;
1434                                 $this->laggedReplicaMode = true;
1435                         }
1436                 }
1437
1438                 return $this->laggedReplicaMode;
1439         }
1440
1441         /**
1442          * @param bool $domain
1443          * @return bool
1444          * @deprecated 1.28; use getLaggedReplicaMode()
1445          */
1446         public function getLaggedSlaveMode( $domain = false ) {
1447                 return $this->getLaggedReplicaMode( $domain );
1448         }
1449
1450         public function laggedReplicaUsed() {
1451                 return $this->laggedReplicaMode;
1452         }
1453
1454         /**
1455          * @return bool
1456          * @since 1.27
1457          * @deprecated Since 1.28; use laggedReplicaUsed()
1458          */
1459         public function laggedSlaveUsed() {
1460                 return $this->laggedReplicaUsed();
1461         }
1462
1463         public function getReadOnlyReason( $domain = false, IDatabase $conn = null ) {
1464                 if ( $this->readOnlyReason !== false ) {
1465                         return $this->readOnlyReason;
1466                 } elseif ( $this->getLaggedReplicaMode( $domain ) ) {
1467                         if ( $this->allReplicasDownMode ) {
1468                                 return 'The database has been automatically locked ' .
1469                                         'until the replica database servers become available';
1470                         } else {
1471                                 return 'The database has been automatically locked ' .
1472                                         'while the replica database servers catch up to the master.';
1473                         }
1474                 } elseif ( $this->masterRunningReadOnly( $domain, $conn ) ) {
1475                         return 'The database master is running in read-only mode.';
1476                 }
1477
1478                 return false;
1479         }
1480
1481         /**
1482          * @param string $domain Domain ID, or false for the current domain
1483          * @param IDatabase|null $conn DB master connectionl used to avoid loops [optional]
1484          * @return bool
1485          */
1486         private function masterRunningReadOnly( $domain, IDatabase $conn = null ) {
1487                 $cache = $this->wanCache;
1488                 $masterServer = $this->getServerName( $this->getWriterIndex() );
1489
1490                 return (bool)$cache->getWithSetCallback(
1491                         $cache->makeGlobalKey( __CLASS__, 'server-read-only', $masterServer ),
1492                         self::TTL_CACHE_READONLY,
1493                         function () use ( $domain, $conn ) {
1494                                 $old = $this->trxProfiler->setSilenced( true );
1495                                 try {
1496                                         $dbw = $conn ?: $this->getConnection( self::DB_MASTER, [], $domain );
1497                                         $readOnly = (int)$dbw->serverIsReadOnly();
1498                                         if ( !$conn ) {
1499                                                 $this->reuseConnection( $dbw );
1500                                         }
1501                                 } catch ( DBError $e ) {
1502                                         $readOnly = 0;
1503                                 }
1504                                 $this->trxProfiler->setSilenced( $old );
1505                                 return $readOnly;
1506                         },
1507                         [ 'pcTTL' => $cache::TTL_PROC_LONG, 'busyValue' => 0 ]
1508                 );
1509         }
1510
1511         public function allowLagged( $mode = null ) {
1512                 if ( $mode === null ) {
1513                         return $this->mAllowLagged;
1514                 }
1515                 $this->mAllowLagged = $mode;
1516
1517                 return $this->mAllowLagged;
1518         }
1519
1520         public function pingAll() {
1521                 $success = true;
1522                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$success ) {
1523                         if ( !$conn->ping() ) {
1524                                 $success = false;
1525                         }
1526                 } );
1527
1528                 return $success;
1529         }
1530
1531         public function forEachOpenConnection( $callback, array $params = [] ) {
1532                 foreach ( $this->mConns as $connsByServer ) {
1533                         foreach ( $connsByServer as $serverConns ) {
1534                                 foreach ( $serverConns as $conn ) {
1535                                         $mergedParams = array_merge( [ $conn ], $params );
1536                                         call_user_func_array( $callback, $mergedParams );
1537                                 }
1538                         }
1539                 }
1540         }
1541
1542         public function forEachOpenMasterConnection( $callback, array $params = [] ) {
1543                 $masterIndex = $this->getWriterIndex();
1544                 foreach ( $this->mConns as $connsByServer ) {
1545                         if ( isset( $connsByServer[$masterIndex] ) ) {
1546                                 /** @var IDatabase $conn */
1547                                 foreach ( $connsByServer[$masterIndex] as $conn ) {
1548                                         $mergedParams = array_merge( [ $conn ], $params );
1549                                         call_user_func_array( $callback, $mergedParams );
1550                                 }
1551                         }
1552                 }
1553         }
1554
1555         public function forEachOpenReplicaConnection( $callback, array $params = [] ) {
1556                 foreach ( $this->mConns as $connsByServer ) {
1557                         foreach ( $connsByServer as $i => $serverConns ) {
1558                                 if ( $i === $this->getWriterIndex() ) {
1559                                         continue; // skip master
1560                                 }
1561                                 foreach ( $serverConns as $conn ) {
1562                                         $mergedParams = array_merge( [ $conn ], $params );
1563                                         call_user_func_array( $callback, $mergedParams );
1564                                 }
1565                         }
1566                 }
1567         }
1568
1569         public function getMaxLag( $domain = false ) {
1570                 $maxLag = -1;
1571                 $host = '';
1572                 $maxIndex = 0;
1573
1574                 if ( $this->getServerCount() <= 1 ) {
1575                         return [ $host, $maxLag, $maxIndex ]; // no replication = no lag
1576                 }
1577
1578                 $lagTimes = $this->getLagTimes( $domain );
1579                 foreach ( $lagTimes as $i => $lag ) {
1580                         if ( $this->mLoads[$i] > 0 && $lag > $maxLag ) {
1581                                 $maxLag = $lag;
1582                                 $host = $this->mServers[$i]['host'];
1583                                 $maxIndex = $i;
1584                         }
1585                 }
1586
1587                 return [ $host, $maxLag, $maxIndex ];
1588         }
1589
1590         public function getLagTimes( $domain = false ) {
1591                 if ( $this->getServerCount() <= 1 ) {
1592                         return [ $this->getWriterIndex() => 0 ]; // no replication = no lag
1593                 }
1594
1595                 $knownLagTimes = []; // map of (server index => 0 seconds)
1596                 $indexesWithLag = [];
1597                 foreach ( $this->mServers as $i => $server ) {
1598                         if ( empty( $server['is static'] ) ) {
1599                                 $indexesWithLag[] = $i; // DB server might have replication lag
1600                         } else {
1601                                 $knownLagTimes[$i] = 0; // DB server is a non-replicating and read-only archive
1602                         }
1603                 }
1604
1605                 return $this->getLoadMonitor()->getLagTimes( $indexesWithLag, $domain ) + $knownLagTimes;
1606         }
1607
1608         public function safeGetLag( IDatabase $conn ) {
1609                 if ( $this->getServerCount() <= 1 ) {
1610                         return 0;
1611                 } else {
1612                         return $conn->getLag();
1613                 }
1614         }
1615
1616         /**
1617          * @param IDatabase $conn
1618          * @param DBMasterPos|bool $pos
1619          * @param int $timeout
1620          * @return bool
1621          */
1622         public function safeWaitForMasterPos( IDatabase $conn, $pos = false, $timeout = 10 ) {
1623                 if ( $this->getServerCount() <= 1 || !$conn->getLBInfo( 'replica' ) ) {
1624                         return true; // server is not a replica DB
1625                 }
1626
1627                 if ( !$pos ) {
1628                         // Get the current master position, opening a connection if needed
1629                         $masterConn = $this->getAnyOpenConnection( $this->getWriterIndex() );
1630                         if ( $masterConn ) {
1631                                 $pos = $masterConn->getMasterPos();
1632                         } else {
1633                                 $masterConn = $this->openConnection( $this->getWriterIndex(), self::DOMAIN_ANY );
1634                                 $pos = $masterConn->getMasterPos();
1635                                 $this->closeConnection( $masterConn );
1636                         }
1637                 }
1638
1639                 if ( $pos instanceof DBMasterPos ) {
1640                         $result = $conn->masterPosWait( $pos, $timeout );
1641                         if ( $result == -1 || is_null( $result ) ) {
1642                                 $msg = __METHOD__ . ': Timed out waiting on {host} pos {pos}';
1643                                 $this->replLogger->warning( $msg,
1644                                         [ 'host' => $conn->getServer(), 'pos' => $pos ] );
1645                                 $ok = false;
1646                         } else {
1647                                 $this->replLogger->info( __METHOD__ . ': Done' );
1648                                 $ok = true;
1649                         }
1650                 } else {
1651                         $ok = false; // something is misconfigured
1652                         $this->replLogger->error( 'Could not get master pos for {host}',
1653                                 [ 'host' => $conn->getServer() ] );
1654                 }
1655
1656                 return $ok;
1657         }
1658
1659         public function setTransactionListener( $name, callable $callback = null ) {
1660                 if ( $callback ) {
1661                         $this->trxRecurringCallbacks[$name] = $callback;
1662                 } else {
1663                         unset( $this->trxRecurringCallbacks[$name] );
1664                 }
1665                 $this->forEachOpenMasterConnection(
1666                         function ( IDatabase $conn ) use ( $name, $callback ) {
1667                                 $conn->setTransactionListener( $name, $callback );
1668                         }
1669                 );
1670         }
1671
1672         public function setTableAliases( array $aliases ) {
1673                 $this->tableAliases = $aliases;
1674         }
1675
1676         public function setDomainPrefix( $prefix ) {
1677                 // Find connections to explicit foreign domains still marked as in-use...
1678                 $domainsInUse = [];
1679                 $this->forEachOpenConnection( function ( IDatabase $conn ) use ( &$domainsInUse ) {
1680                         // Once reuseConnection() is called on a handle, its reference count goes from 1 to 0.
1681                         // Until then, it is still in use by the caller (explicitly or via DBConnRef scope).
1682                         if ( $conn->getLBInfo( 'foreignPoolRefCount' ) > 0 ) {
1683                                 $domainsInUse[] = $conn->getDomainID();
1684                         }
1685                 } );
1686
1687                 // Do not switch connections to explicit foreign domains unless marked as safe
1688                 if ( $domainsInUse ) {
1689                         $domains = implode( ', ', $domainsInUse );
1690                         throw new DBUnexpectedError( null,
1691                                 "Foreign domain connections are still in use ($domains)." );
1692                 }
1693
1694                 $this->localDomain = new DatabaseDomain(
1695                         $this->localDomain->getDatabase(),
1696                         null,
1697                         $prefix
1698                 );
1699
1700                 $this->forEachOpenConnection( function ( IDatabase $db ) use ( $prefix ) {
1701                         $db->tablePrefix( $prefix );
1702                 } );
1703         }
1704
1705         /**
1706          * Make PHP ignore user aborts/disconnects until the returned
1707          * value leaves scope. This returns null and does nothing in CLI mode.
1708          *
1709          * @return ScopedCallback|null
1710          */
1711         final protected function getScopedPHPBehaviorForCommit() {
1712                 if ( PHP_SAPI != 'cli' ) { // https://bugs.php.net/bug.php?id=47540
1713                         $old = ignore_user_abort( true ); // avoid half-finished operations
1714                         return new ScopedCallback( function () use ( $old ) {
1715                                 ignore_user_abort( $old );
1716                         } );
1717                 }
1718
1719                 return null;
1720         }
1721
1722         function __destruct() {
1723                 // Avoid connection leaks for sanity
1724                 $this->disable();
1725         }
1726 }
1727
1728 class_alias( LoadBalancer::class, 'LoadBalancer' );