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