maintenance/storage/recompressTracked.php

   1 <?php
   2 /**
   3  * Moves blobs indexed by trackBlobs.php to a specified list of destination
   4  * clusters, and recompresses them in the process.
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 2 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License along
  17  * with this program; if not, write to the Free Software Foundation, Inc.,
  18  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  19  * http://www.gnu.org/copyleft/gpl.html
  20  *
  21  * @file
  22  * @ingroup Maintenance ExternalStorage
  23  */
  24
  25 use MediaWiki\Logger\LegacyLogger;
  26
  27 $optionsWithArgs = RecompressTracked::getOptionsWithArgs();
  28 require __DIR__ . '/../commandLine.inc';
  29
  30 if ( count( $args ) < 1 ) {
  31         echo "Usage: php recompressTracked.php [options] <cluster> [... <cluster>...]
  32 Moves blobs indexed by trackBlobs.php to a specified list of destination clusters,
  33 and recompresses them in the process. Restartable.
  34
  35 Options:
  36         --procs <procs>       Set the number of child processes (default 1)
  37         --copy-only           Copy only, do not update the text table. Restart
  38                               without this option to complete.
  39         --debug-log <file>    Log debugging data to the specified file
  40         --info-log <file>     Log progress messages to the specified file
  41         --critical-log <file> Log error messages to the specified file
  42 ";
  43         exit( 1 );
  44 }
  45
  46 $job = RecompressTracked::newFromCommandLine( $args, $options );
  47 $job->execute();
  48
  49 /**
  50  * Maintenance script that moves blobs indexed by trackBlobs.php to a specified
  51  * list of destination clusters, and recompresses them in the process.
  52  *
  53  * @ingroup Maintenance ExternalStorage
  54  */
  55 class RecompressTracked {
  56         public $destClusters;
  57         public $batchSize = 1000;
  58         public $orphanBatchSize = 1000;
  59         public $reportingInterval = 10;
  60         public $numProcs = 1;
  61         public $useDiff, $pageBlobClass, $orphanBlobClass;
  62         public $slavePipes, $slaveProcs, $prevSlaveId;
  63         public $copyOnly = false;
  64         public $isChild = false;
  65         public $slaveId = false;
  66         public $noCount = false;
  67         public $debugLog, $infoLog, $criticalLog;
  68         public $store;
  69
  70         private static $optionsWithArgs = array(
  71                 'procs',
  72                 'slave-id',
  73                 'debug-log',
  74                 'info-log',
  75                 'critical-log'
  76         );
  77
  78         private static $cmdLineOptionMap = array(
  79                 'no-count' => 'noCount',
  80                 'procs' => 'numProcs',
  81                 'copy-only' => 'copyOnly',
  82                 'child' => 'isChild',
  83                 'slave-id' => 'slaveId',
  84                 'debug-log' => 'debugLog',
  85                 'info-log' => 'infoLog',
  86                 'critical-log' => 'criticalLog',
  87         );
  88
  89         static function getOptionsWithArgs() {
  90                 return self::$optionsWithArgs;
  91         }
  92
  93         static function newFromCommandLine( $args, $options ) {
  94                 $jobOptions = array( 'destClusters' => $args );
  95                 foreach ( self::$cmdLineOptionMap as $cmdOption => $classOption ) {
  96                         if ( isset( $options[$cmdOption] ) ) {
  97                                 $jobOptions[$classOption] = $options[$cmdOption];
  98                         }
  99                 }
 100
 101                 return new self( $jobOptions );
 102         }
 103
 104         function __construct( $options ) {
 105                 foreach ( $options as $name => $value ) {
 106                         $this->$name = $value;
 107                 }
 108                 $this->store = new ExternalStoreDB;
 109                 if ( !$this->isChild ) {
 110                         $GLOBALS['wgDebugLogPrefix'] = "RCT M: ";
 111                 } elseif ( $this->slaveId !== false ) {
 112                         $GLOBALS['wgDebugLogPrefix'] = "RCT {$this->slaveId}: ";
 113                 }
 114                 $this->useDiff = function_exists( 'xdiff_string_bdiff' );
 115                 $this->pageBlobClass = $this->useDiff ? 'DiffHistoryBlob' : 'ConcatenatedGzipHistoryBlob';
 116                 $this->orphanBlobClass = 'ConcatenatedGzipHistoryBlob';
 117         }
 118
 119         function debug( $msg ) {
 120                 wfDebug( "$msg\n" );
 121                 if ( $this->debugLog ) {
 122                         $this->logToFile( $msg, $this->debugLog );
 123                 }
 124         }
 125
 126         function info( $msg ) {
 127                 echo "$msg\n";
 128                 if ( $this->infoLog ) {
 129                         $this->logToFile( $msg, $this->infoLog );
 130                 }
 131         }
 132
 133         function critical( $msg ) {
 134                 echo "$msg\n";
 135                 if ( $this->criticalLog ) {
 136                         $this->logToFile( $msg, $this->criticalLog );
 137                 }
 138         }
 139
 140         function logToFile( $msg, $file ) {
 141                 $header = '[' . date( 'd\TH:i:s' ) . '] ' . wfHostname() . ' ' . posix_getpid();
 142                 if ( $this->slaveId !== false ) {
 143                         $header .= "({$this->slaveId})";
 144                 }
 145                 $header .= ' ' . wfWikiID();
 146                 LegacyLogger::emit( sprintf( "%-50s %s\n", $header, $msg ), $file );
 147         }
 148
 149         /**
 150          * Wait until the selected slave has caught up to the master.
 151          * This allows us to use the slave for things that were committed in a
 152          * previous part of this batch process.
 153          */
 154         function syncDBs() {
 155                 $dbw = wfGetDB( DB_MASTER );
 156                 $dbr = wfGetDB( DB_SLAVE );
 157                 $pos = $dbw->getMasterPos();
 158                 $dbr->masterPosWait( $pos, 100000 );
 159         }
 160
 161         /**
 162          * Execute parent or child depending on the isChild option
 163          */
 164         function execute() {
 165                 if ( $this->isChild ) {
 166                         $this->executeChild();
 167                 } else {
 168                         $this->executeParent();
 169                 }
 170         }
 171
 172         /**
 173          * Execute the parent process
 174          */
 175         function executeParent() {
 176                 if ( !$this->checkTrackingTable() ) {
 177                         return;
 178                 }
 179
 180                 $this->syncDBs();
 181                 $this->startSlaveProcs();
 182                 $this->doAllPages();
 183                 $this->doAllOrphans();
 184                 $this->killSlaveProcs();
 185         }
 186
 187         /**
 188          * Make sure the tracking table exists and isn't empty
 189          * @return bool
 190          */
 191         function checkTrackingTable() {
 192                 $dbr = wfGetDB( DB_SLAVE );
 193                 if ( !$dbr->tableExists( 'blob_tracking' ) ) {
 194                         $this->critical( "Error: blob_tracking table does not exist" );
 195
 196                         return false;
 197                 }
 198                 $row = $dbr->selectRow( 'blob_tracking', '*', false, __METHOD__ );
 199                 if ( !$row ) {
 200                         $this->info( "Warning: blob_tracking table contains no rows, skipping this wiki." );
 201
 202                         return false;
 203                 }
 204
 205                 return true;
 206         }
 207
 208         /**
 209          * Start the worker processes.
 210          * These processes will listen on stdin for commands.
 211          * This necessary because text recompression is slow: loading, compressing and
 212          * writing are all slow.
 213          */
 214         function startSlaveProcs() {
 215                 $cmd = 'php ' . wfEscapeShellArg( __FILE__ );
 216                 foreach ( self::$cmdLineOptionMap as $cmdOption => $classOption ) {
 217                         if ( $cmdOption == 'slave-id' ) {
 218                                 continue;
 219                         } elseif ( in_array( $cmdOption, self::$optionsWithArgs ) && isset( $this->$classOption ) ) {
 220                                 $cmd .= " --$cmdOption " . wfEscapeShellArg( $this->$classOption );
 221                         } elseif ( $this->$classOption ) {
 222                                 $cmd .= " --$cmdOption";
 223                         }
 224                 }
 225                 $cmd .= ' --child' .
 226                         ' --wiki ' . wfEscapeShellArg( wfWikiID() ) .
 227                         ' ' . call_user_func_array( 'wfEscapeShellArg', $this->destClusters );
 228
 229                 $this->slavePipes = $this->slaveProcs = array();
 230                 for ( $i = 0; $i < $this->numProcs; $i++ ) {
 231                         $pipes = false;
 232                         $spec = array(
 233                                 array( 'pipe', 'r' ),
 234                                 array( 'file', 'php://stdout', 'w' ),
 235                                 array( 'file', 'php://stderr', 'w' )
 236                         );
 237                         MediaWiki\suppressWarnings();
 238                         $proc = proc_open( "$cmd --slave-id $i", $spec, $pipes );
 239                         MediaWiki\restoreWarnings();
 240                         if ( !$proc ) {
 241                                 $this->critical( "Error opening slave process: $cmd" );
 242                                 exit( 1 );
 243                         }
 244                         $this->slaveProcs[$i] = $proc;
 245                         $this->slavePipes[$i] = $pipes[0];
 246                 }
 247                 $this->prevSlaveId = -1;
 248         }
 249
 250         /**
 251          * Gracefully terminate the child processes
 252          */
 253         function killSlaveProcs() {
 254                 $this->info( "Waiting for slave processes to finish..." );
 255                 for ( $i = 0; $i < $this->numProcs; $i++ ) {
 256                         $this->dispatchToSlave( $i, 'quit' );
 257                 }
 258                 for ( $i = 0; $i < $this->numProcs; $i++ ) {
 259                         $status = proc_close( $this->slaveProcs[$i] );
 260                         if ( $status ) {
 261                                 $this->critical( "Warning: child #$i exited with status $status" );
 262                         }
 263                 }
 264                 $this->info( "Done." );
 265         }
 266
 267         /**
 268          * Dispatch a command to the next available slave.
 269          * This may block until a slave finishes its work and becomes available.
 270          */
 271         function dispatch( /*...*/ ) {
 272                 $args = func_get_args();
 273                 $pipes = $this->slavePipes;
 274                 $numPipes = stream_select( $x = array(), $pipes, $y = array(), 3600 );
 275                 if ( !$numPipes ) {
 276                         $this->critical( "Error waiting to write to slaves. Aborting" );
 277                         exit( 1 );
 278                 }
 279                 for ( $i = 0; $i < $this->numProcs; $i++ ) {
 280                         $slaveId = ( $i + $this->prevSlaveId + 1 ) % $this->numProcs;
 281                         if ( isset( $pipes[$slaveId] ) ) {
 282                                 $this->prevSlaveId = $slaveId;
 283                                 $this->dispatchToSlave( $slaveId, $args );
 284
 285                                 return;
 286                         }
 287                 }
 288                 $this->critical( "Unreachable" );
 289                 exit( 1 );
 290         }
 291
 292         /**
 293          * Dispatch a command to a specified slave
 294          * @param int $slaveId
 295          * @param array|string $args
 296          */
 297         function dispatchToSlave( $slaveId, $args ) {
 298                 $args = (array)$args;
 299                 $cmd = implode( ' ', $args );
 300                 fwrite( $this->slavePipes[$slaveId], "$cmd\n" );
 301         }
 302
 303         /**
 304          * Move all tracked pages to the new clusters
 305          */
 306         function doAllPages() {
 307                 $dbr = wfGetDB( DB_SLAVE );
 308                 $i = 0;
 309                 $startId = 0;
 310                 if ( $this->noCount ) {
 311                         $numPages = '[unknown]';
 312                 } else {
 313                         $numPages = $dbr->selectField( 'blob_tracking',
 314                                 'COUNT(DISTINCT bt_page)',
 315                                 # A condition is required so that this query uses the index
 316                                 array( 'bt_moved' => 0 ),
 317                                 __METHOD__
 318                         );
 319                 }
 320                 if ( $this->copyOnly ) {
 321                         $this->info( "Copying pages..." );
 322                 } else {
 323                         $this->info( "Moving pages..." );
 324                 }
 325                 while ( true ) {
 326                         $res = $dbr->select( 'blob_tracking',
 327                                 array( 'bt_page' ),
 328                                 array(
 329                                         'bt_moved' => 0,
 330                                         'bt_page > ' . $dbr->addQuotes( $startId )
 331                                 ),
 332                                 __METHOD__,
 333                                 array(
 334                                         'DISTINCT',
 335                                         'ORDER BY' => 'bt_page',
 336                                         'LIMIT' => $this->batchSize,
 337                                 )
 338                         );
 339                         if ( !$res->numRows() ) {
 340                                 break;
 341                         }
 342                         foreach ( $res as $row ) {
 343                                 $this->dispatch( 'doPage', $row->bt_page );
 344                                 $i++;
 345                         }
 346                         $startId = $row->bt_page;
 347                         $this->report( 'pages', $i, $numPages );
 348                 }
 349                 $this->report( 'pages', $i, $numPages );
 350                 if ( $this->copyOnly ) {
 351                         $this->info( "All page copies queued." );
 352                 } else {
 353                         $this->info( "All page moves queued." );
 354                 }
 355         }
 356
 357         /**
 358          * Display a progress report
 359          * @param string $label
 360          * @param int $current
 361          * @param int $end
 362          */
 363         function report( $label, $current, $end ) {
 364                 $this->numBatches++;
 365                 if ( $current == $end || $this->numBatches >= $this->reportingInterval ) {
 366                         $this->numBatches = 0;
 367                         $this->info( "$label: $current / $end" );
 368                         $this->waitForSlaves();
 369                 }
 370         }
 371
 372         /**
 373          * Move all orphan text to the new clusters
 374          */
 375         function doAllOrphans() {
 376                 $dbr = wfGetDB( DB_SLAVE );
 377                 $startId = 0;
 378                 $i = 0;
 379                 if ( $this->noCount ) {
 380                         $numOrphans = '[unknown]';
 381                 } else {
 382                         $numOrphans = $dbr->selectField( 'blob_tracking',
 383                                 'COUNT(DISTINCT bt_text_id)',
 384                                 array( 'bt_moved' => 0, 'bt_page' => 0 ),
 385                                 __METHOD__ );
 386                         if ( !$numOrphans ) {
 387                                 return;
 388                         }
 389                 }
 390                 if ( $this->copyOnly ) {
 391                         $this->info( "Copying orphans..." );
 392                 } else {
 393                         $this->info( "Moving orphans..." );
 394                 }
 395
 396                 while ( true ) {
 397                         $res = $dbr->select( 'blob_tracking',
 398                                 array( 'bt_text_id' ),
 399                                 array(
 400                                         'bt_moved' => 0,
 401                                         'bt_page' => 0,
 402                                         'bt_text_id > ' . $dbr->addQuotes( $startId )
 403                                 ),
 404                                 __METHOD__,
 405                                 array(
 406                                         'DISTINCT',
 407                                         'ORDER BY' => 'bt_text_id',
 408                                         'LIMIT' => $this->batchSize
 409                                 )
 410                         );
 411                         if ( !$res->numRows() ) {
 412                                 break;
 413                         }
 414                         $ids = array();
 415                         foreach ( $res as $row ) {
 416                                 $ids[] = $row->bt_text_id;
 417                                 $i++;
 418                         }
 419                         // Need to send enough orphan IDs to the child at a time to fill a blob,
 420                         // so orphanBatchSize needs to be at least ~100.
 421                         // batchSize can be smaller or larger.
 422                         while ( count( $ids ) > $this->orphanBatchSize ) {
 423                                 $args = array_slice( $ids, 0, $this->orphanBatchSize );
 424                                 $ids = array_slice( $ids, $this->orphanBatchSize );
 425                                 array_unshift( $args, 'doOrphanList' );
 426                                 call_user_func_array( array( $this, 'dispatch' ), $args );
 427                         }
 428                         if ( count( $ids ) ) {
 429                                 $args = $ids;
 430                                 array_unshift( $args, 'doOrphanList' );
 431                                 call_user_func_array( array( $this, 'dispatch' ), $args );
 432                         }
 433
 434                         $startId = $row->bt_text_id;
 435                         $this->report( 'orphans', $i, $numOrphans );
 436                 }
 437                 $this->report( 'orphans', $i, $numOrphans );
 438                 $this->info( "All orphans queued." );
 439         }
 440
 441         /**
 442          * Main entry point for worker processes
 443          */
 444         function executeChild() {
 445                 $this->debug( 'starting' );
 446                 $this->syncDBs();
 447
 448                 while ( !feof( STDIN ) ) {
 449                         $line = rtrim( fgets( STDIN ) );
 450                         if ( $line == '' ) {
 451                                 continue;
 452                         }
 453                         $this->debug( $line );
 454                         $args = explode( ' ', $line );
 455                         $cmd = array_shift( $args );
 456                         switch ( $cmd ) {
 457                                 case 'doPage':
 458                                         $this->doPage( intval( $args[0] ) );
 459                                         break;
 460                                 case 'doOrphanList':
 461                                         $this->doOrphanList( array_map( 'intval', $args ) );
 462                                         break;
 463                                 case 'quit':
 464                                         return;
 465                         }
 466                         $this->waitForSlaves();
 467                 }
 468         }
 469
 470         /**
 471          * Move tracked text in a given page
 472          *
 473          * @param int $pageId
 474          */
 475         function doPage( $pageId ) {
 476                 $title = Title::newFromID( $pageId );
 477                 if ( $title ) {
 478                         $titleText = $title->getPrefixedText();
 479                 } else {
 480                         $titleText = '[deleted]';
 481                 }
 482                 $dbr = wfGetDB( DB_SLAVE );
 483
 484                 // Finish any incomplete transactions
 485                 if ( !$this->copyOnly ) {
 486                         $this->finishIncompleteMoves( array( 'bt_page' => $pageId ) );
 487                         $this->syncDBs();
 488                 }
 489
 490                 $startId = 0;
 491                 $trx = new CgzCopyTransaction( $this, $this->pageBlobClass );
 492
 493                 while ( true ) {
 494                         $res = $dbr->select(
 495                                 array( 'blob_tracking', 'text' ),
 496                                 '*',
 497                                 array(
 498                                         'bt_page' => $pageId,
 499                                         'bt_text_id > ' . $dbr->addQuotes( $startId ),
 500                                         'bt_moved' => 0,
 501                                         'bt_new_url IS NULL',
 502                                         'bt_text_id=old_id',
 503                                 ),
 504                                 __METHOD__,
 505                                 array(
 506                                         'ORDER BY' => 'bt_text_id',
 507                                         'LIMIT' => $this->batchSize
 508                                 )
 509                         );
 510                         if ( !$res->numRows() ) {
 511                                 break;
 512                         }
 513
 514                         $lastTextId = 0;
 515                         foreach ( $res as $row ) {
 516                                 if ( $lastTextId == $row->bt_text_id ) {
 517                                         // Duplicate (null edit)
 518                                         continue;
 519                                 }
 520                                 $lastTextId = $row->bt_text_id;
 521                                 // Load the text
 522                                 $text = Revision::getRevisionText( $row );
 523                                 if ( $text === false ) {
 524                                         $this->critical( "Error loading {$row->bt_rev_id}/{$row->bt_text_id}" );
 525                                         continue;
 526                                 }
 527
 528                                 // Queue it
 529                                 if ( !$trx->addItem( $text, $row->bt_text_id ) ) {
 530                                         $this->debug( "$titleText: committing blob with " . $trx->getSize() . " items" );
 531                                         $trx->commit();
 532                                         $trx = new CgzCopyTransaction( $this, $this->pageBlobClass );
 533                                         $this->waitForSlaves();
 534                                 }
 535                         }
 536                         $startId = $row->bt_text_id;
 537                 }
 538
 539                 $this->debug( "$titleText: committing blob with " . $trx->getSize() . " items" );
 540                 $trx->commit();
 541         }
 542
 543         /**
 544          * Atomic move operation.
 545          *
 546          * Write the new URL to the text table and set the bt_moved flag.
 547          *
 548          * This is done in a single transaction to provide restartable behavior
 549          * without data loss.
 550          *
 551          * The transaction is kept short to reduce locking.
 552          *
 553          * @param int $textId
 554          * @param string $url
 555          */
 556         function moveTextRow( $textId, $url ) {
 557                 if ( $this->copyOnly ) {
 558                         $this->critical( "Internal error: can't call moveTextRow() in --copy-only mode" );
 559                         exit( 1 );
 560                 }
 561                 $dbw = wfGetDB( DB_MASTER );
 562                 $dbw->begin( __METHOD__ );
 563                 $dbw->update( 'text',
 564                         array( // set
 565                                 'old_text' => $url,
 566                                 'old_flags' => 'external,utf-8',
 567                         ),
 568                         array( // where
 569                                 'old_id' => $textId
 570                         ),
 571                         __METHOD__
 572                 );
 573                 $dbw->update( 'blob_tracking',
 574                         array( 'bt_moved' => 1 ),
 575                         array( 'bt_text_id' => $textId ),
 576                         __METHOD__
 577                 );
 578                 $dbw->commit( __METHOD__ );
 579         }
 580
 581         /**
 582          * Moves are done in two phases: bt_new_url and then bt_moved.
 583          *  - bt_new_url indicates that the text has been copied to the new cluster.
 584          *  - bt_moved indicates that the text table has been updated.
 585          *
 586          * This function completes any moves that only have done bt_new_url. This
 587          * can happen when the script is interrupted, or when --copy-only is used.
 588          *
 589          * @param array $conds
 590          */
 591         function finishIncompleteMoves( $conds ) {
 592                 $dbr = wfGetDB( DB_SLAVE );
 593
 594                 $startId = 0;
 595                 $conds = array_merge( $conds, array(
 596                         'bt_moved' => 0,
 597                         'bt_new_url IS NOT NULL'
 598                 ) );
 599                 while ( true ) {
 600                         $res = $dbr->select( 'blob_tracking',
 601                                 '*',
 602                                 array_merge( $conds, array( 'bt_text_id > ' . $dbr->addQuotes( $startId ) ) ),
 603                                 __METHOD__,
 604                                 array(
 605                                         'ORDER BY' => 'bt_text_id',
 606                                         'LIMIT' => $this->batchSize,
 607                                 )
 608                         );
 609                         if ( !$res->numRows() ) {
 610                                 break;
 611                         }
 612                         $this->debug( 'Incomplete: ' . $res->numRows() . ' rows' );
 613                         foreach ( $res as $row ) {
 614                                 $this->moveTextRow( $row->bt_text_id, $row->bt_new_url );
 615                                 if ( $row->bt_text_id % 10 == 0 ) {
 616                                         $this->waitForSlaves();
 617                                 }
 618                         }
 619                         $startId = $row->bt_text_id;
 620                 }
 621         }
 622
 623         /**
 624          * Returns the name of the next target cluster
 625          * @return string
 626          */
 627         function getTargetCluster() {
 628                 $cluster = next( $this->destClusters );
 629                 if ( $cluster === false ) {
 630                         $cluster = reset( $this->destClusters );
 631                 }
 632
 633                 return $cluster;
 634         }
 635
 636         /**
 637          * Gets a DB master connection for the given external cluster name
 638          * @param string $cluster
 639          * @return DatabaseBase
 640          */
 641         function getExtDB( $cluster ) {
 642                 $lb = wfGetLBFactory()->getExternalLB( $cluster );
 643
 644                 return $lb->getConnection( DB_MASTER );
 645         }
 646
 647         /**
 648          * Move an orphan text_id to the new cluster
 649          *
 650          * @param array $textIds
 651          */
 652         function doOrphanList( $textIds ) {
 653                 // Finish incomplete moves
 654                 if ( !$this->copyOnly ) {
 655                         $this->finishIncompleteMoves( array( 'bt_text_id' => $textIds ) );
 656                         $this->syncDBs();
 657                 }
 658
 659                 $trx = new CgzCopyTransaction( $this, $this->orphanBlobClass );
 660
 661                 $res = wfGetDB( DB_SLAVE )->select(
 662                         array( 'text', 'blob_tracking' ),
 663                         array( 'old_id', 'old_text', 'old_flags' ),
 664                         array(
 665                                 'old_id' => $textIds,
 666                                 'bt_text_id=old_id',
 667                                 'bt_moved' => 0,
 668                         ),
 669                         __METHOD__,
 670                         array( 'DISTINCT' )
 671                 );
 672
 673                 foreach ( $res as $row ) {
 674                         $text = Revision::getRevisionText( $row );
 675                         if ( $text === false ) {
 676                                 $this->critical( "Error: cannot load revision text for old_id={$row->old_id}" );
 677                                 continue;
 678                         }
 679
 680                         if ( !$trx->addItem( $text, $row->old_id ) ) {
 681                                 $this->debug( "[orphan]: committing blob with " . $trx->getSize() . " rows" );
 682                                 $trx->commit();
 683                                 $trx = new CgzCopyTransaction( $this, $this->orphanBlobClass );
 684                                 $this->waitForSlaves();
 685                         }
 686                 }
 687                 $this->debug( "[orphan]: committing blob with " . $trx->getSize() . " rows" );
 688                 $trx->commit();
 689         }
 690
 691         /**
 692          * Wait for slaves (quietly)
 693          */
 694         function waitForSlaves() {
 695                 $lb = wfGetLB();
 696                 while ( true ) {
 697                         list( $host, $maxLag ) = $lb->getMaxLag();
 698                         if ( $maxLag < 2 ) {
 699                                 break;
 700                         }
 701                         sleep( 5 );
 702                 }
 703         }
 704 }
 705
 706 /**
 707  * Class to represent a recompression operation for a single CGZ blob
 708  */
 709 class CgzCopyTransaction {
 710         public $parent;
 711         public $blobClass;
 712         public $cgz;
 713         public $referrers;
 714
 715         /**
 716          * Create a transaction from a RecompressTracked object
 717          * @param RecompressTracked $parent
 718          * @param string $blobClass
 719          */
 720         function __construct( $parent, $blobClass ) {
 721                 $this->blobClass = $blobClass;
 722                 $this->cgz = false;
 723                 $this->texts = array();
 724                 $this->parent = $parent;
 725         }
 726
 727         /**
 728          * Add text.
 729          * Returns false if it's ready to commit.
 730          * @param string $text
 731          * @param int $textId
 732          * @return bool
 733          */
 734         function addItem( $text, $textId ) {
 735                 if ( !$this->cgz ) {
 736                         $class = $this->blobClass;
 737                         $this->cgz = new $class;
 738                 }
 739                 $hash = $this->cgz->addItem( $text );
 740                 $this->referrers[$textId] = $hash;
 741                 $this->texts[$textId] = $text;
 742
 743                 return $this->cgz->isHappy();
 744         }
 745
 746         function getSize() {
 747                 return count( $this->texts );
 748         }
 749
 750         /**
 751          * Recompress text after some aberrant modification
 752          */
 753         function recompress() {
 754                 $class = $this->blobClass;
 755                 $this->cgz = new $class;
 756                 $this->referrers = array();
 757                 foreach ( $this->texts as $textId => $text ) {
 758                         $hash = $this->cgz->addItem( $text );
 759                         $this->referrers[$textId] = $hash;
 760                 }
 761         }
 762
 763         /**
 764          * Commit the blob.
 765          * Does nothing if no text items have been added.
 766          * May skip the move if --copy-only is set.
 767          */
 768         function commit() {
 769                 $originalCount = count( $this->texts );
 770                 if ( !$originalCount ) {
 771                         return;
 772                 }
 773
 774                 // Check to see if the target text_ids have been moved already.
 775                 //
 776                 // We originally read from the slave, so this can happen when a single
 777                 // text_id is shared between multiple pages. It's rare, but possible
 778                 // if a delete/move/undelete cycle splits up a null edit.
 779                 //
 780                 // We do a locking read to prevent closer-run race conditions.
 781                 $dbw = wfGetDB( DB_MASTER );
 782                 $dbw->begin( __METHOD__ );
 783                 $res = $dbw->select( 'blob_tracking',
 784                         array( 'bt_text_id', 'bt_moved' ),
 785                         array( 'bt_text_id' => array_keys( $this->referrers ) ),
 786                         __METHOD__, array( 'FOR UPDATE' ) );
 787                 $dirty = false;
 788                 foreach ( $res as $row ) {
 789                         if ( $row->bt_moved ) {
 790                                 # This row has already been moved, remove it
 791                                 $this->parent->debug( "TRX: conflict detected in old_id={$row->bt_text_id}" );
 792                                 unset( $this->texts[$row->bt_text_id] );
 793                                 $dirty = true;
 794                         }
 795                 }
 796
 797                 // Recompress the blob if necessary
 798                 if ( $dirty ) {
 799                         if ( !count( $this->texts ) ) {
 800                                 // All have been moved already
 801                                 if ( $originalCount > 1 ) {
 802                                         // This is suspcious, make noise
 803                                         $this->critical( "Warning: concurrent operation detected, are there two conflicting " .
 804                                                 "processes running, doing the same job?" );
 805                                 }
 806
 807                                 return;
 808                         }
 809                         $this->recompress();
 810                 }
 811
 812                 // Insert the data into the destination cluster
 813                 $targetCluster = $this->parent->getTargetCluster();
 814                 $store = $this->parent->store;
 815                 $targetDB = $store->getMaster( $targetCluster );
 816                 $targetDB->clearFlag( DBO_TRX ); // we manage the transactions
 817                 $targetDB->begin( __METHOD__ );
 818                 $baseUrl = $this->parent->store->store( $targetCluster, serialize( $this->cgz ) );
 819
 820                 // Write the new URLs to the blob_tracking table
 821                 foreach ( $this->referrers as $textId => $hash ) {
 822                         $url = $baseUrl . '/' . $hash;
 823                         $dbw->update( 'blob_tracking',
 824                                 array( 'bt_new_url' => $url ),
 825                                 array(
 826                                         'bt_text_id' => $textId,
 827                                         'bt_moved' => 0, # Check for concurrent conflicting update
 828                                 ),
 829                                 __METHOD__
 830                         );
 831                 }
 832
 833                 $targetDB->commit( __METHOD__ );
 834                 // Critical section here: interruption at this point causes blob duplication
 835                 // Reversing the order of the commits would cause data loss instead
 836                 $dbw->commit( __METHOD__ );
 837
 838                 // Write the new URLs to the text table and set the moved flag
 839                 if ( !$this->parent->copyOnly ) {
 840                         foreach ( $this->referrers as $textId => $hash ) {
 841                                 $url = $baseUrl . '/' . $hash;
 842                                 $this->parent->moveTextRow( $textId, $url );
 843                         }
 844                 }
 845         }
 846 }