nextJobDB.php

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<?php
require_once( dirname( __FILE__ ) . '/Maintenance.php' );

class nextJobDB extends Maintenance {
        public function __construct() {
                parent::__construct();
                $this->mDescription = "Pick a database that has pending jobs";
                $this->addOption( 'type', "The type of job to search for", false, true );
        }

        public function execute() {
                global $wgMemc;
                $type = $this->getOption( 'type', false );

                $memcKey = 'jobqueue:dbs:v2';
                $pendingDBs = $wgMemc->get( $memcKey );

                // If the cache entry wasn't present, or in 1% of cases otherwise,
                // regenerate the cache.
                if ( !$pendingDBs || mt_rand( 0, 100 ) == 0 ) {
                        $pendingDBs = $this->getPendingDbs();
                        $wgMemc->set( $memcKey, $pendingDBs, 300 );
                }

                if ( !$pendingDBs ) {
                        return;
                }

                do {
                        $again = false;

                        if ( $type === false ) {
                                $candidates = call_user_func_array( 'array_merge', $pendingDBs );
                        } elseif ( isset( $pendingDBs[$type] ) ) {
                                $candidates = $pendingDBs[$type];
                        } else {
                                $candidates = array();
                        }
                        if ( !$candidates ) {
                                return;
                        }

                        $candidates = array_values( $candidates );
                        $db = $candidates[ mt_rand( 0, count( $candidates ) - 1 ) ];
                        if ( !$this->checkJob( $type, $db ) ) {
                                // This job is not available in the current database. Remove it from
                                // the cache.
                                if ( $type === false ) {
                                        foreach ( $pendingDBs as $type2 => $dbs ) {
                                                $pendingDBs[$type2] = array_diff( $pendingDBs[$type2], array( $db ) );
                                        }
                                } else {
                                        $pendingDBs[$type] = array_diff( $pendingDBs[$type], array( $db ) );
                                }

                                $wgMemc->set( $memcKey, $pendingDBs, 300 );
                                $again = true;
                        }
                } while ( $again );

                $this->output( $db . "\n" );
        }

        function checkJob( $type, $dbName ) {
                $lb = wfGetLB( $dbName );
                $db = $lb->getConnection( DB_MASTER, array(), $dbName );
                if ( $type === false ) {
                        $conds = array();
                } else {
                        $conds = array( 'job_cmd' => $type );
                }

                $exists = (bool) $db->selectField( 'job', '1', $conds, __METHOD__ );
                $lb->reuseConnection( $db );
                return $exists;
        }

        private function getPendingDbs() {
                global $wgLocalDatabases;
                $pendingDBs = array();
                # Cross-reference DBs by master DB server
                $dbsByMaster = array();
                foreach ( $wgLocalDatabases as $db ) {
                        $lb = wfGetLB( $db );
                        $dbsByMaster[$lb->getServerName( 0 )][] = $db;
                }

                foreach ( $dbsByMaster as $dbs ) {
                        $dbConn = wfGetDB( DB_MASTER, array(), $dbs[0] );

                        # Padding row for MySQL bug
                        $pad = str_repeat( '-', 40 );
                        $sql = "(SELECT '$pad' as db, '$pad' as job_cmd)";
                        foreach ( $dbs as $wikiId ) {
                                if ( $sql != '' ) {
                                        $sql .= ' UNION ';
                                }

                                list( $dbName, $tablePrefix ) = wfSplitWikiID( $wikiId );
                                $dbConn->tablePrefix( $tablePrefix );
                                $jobTable = $dbConn->tableName( 'job' );

                                $sql .= "(SELECT DISTINCT '$wikiId' as db, job_cmd FROM $dbName.$jobTable GROUP BY job_cmd)";
                        }
                        $res = $dbConn->query( $sql, __METHOD__ );
                        $first = true;
                        foreach ( $res as $row ) {
                                if ( $first ) {
                                        // discard padding row
                                        $first = false;
                                        continue;
                                }
                                $pendingDBs[$row->job_cmd][] = $row->db;
                        }
                }
                return $pendingDBs;
        }
}

$maintClass = "nextJobDb";
require_once( RUN_MAINTENANCE_IF_MAIN );