objectcache: add WANObjectCacheReaper for assuring purges

[mediawiki.git] / includes / cache / LinkCache.php

<?php
/**
 * Page existence cache.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 * @ingroup Cache
 */
use MediaWiki\Linker\LinkTarget;
use MediaWiki\MediaWikiServices;

/**
 * Cache for article titles (prefixed DB keys) and ids linked from one source
 *
 * @ingroup Cache
 */
class LinkCache {
        /** @var HashBagOStuff */
        private $mGoodLinks;
        /** @var HashBagOStuff */
        private $mBadLinks;
        /** @var WANObjectCache */
        private $wanCache;

        /** @var bool */
        private $mForUpdate = false;

        /** @var TitleFormatter */
        private $titleFormatter;

        /**
         * How many Titles to store. There are two caches, so the amount actually
         * stored in memory can be up to twice this.
         */
        const MAX_SIZE = 10000;

        public function __construct( TitleFormatter $titleFormatter, WANObjectCache $cache ) {
                $this->mGoodLinks = new HashBagOStuff( [ 'maxKeys' => self::MAX_SIZE ] );
                $this->mBadLinks = new HashBagOStuff( [ 'maxKeys' => self::MAX_SIZE ] );
                $this->wanCache = $cache;
                $this->titleFormatter = $titleFormatter;
        }

        /**
         * Get an instance of this class.
         *
         * @return LinkCache
         * @deprecated since 1.28, use MediaWikiServices instead
         */
        public static function singleton() {
                return MediaWikiServices::getInstance()->getLinkCache();
        }

        /**
         * General accessor to get/set whether the master DB should be used
         *
         * This used to also set the FOR UPDATE option (locking the rows read
         * in order to avoid link table inconsistency), which was later removed
         * for performance on wikis with a high edit rate.
         *
         * @param bool $update
         * @return bool
         */
        public function forUpdate( $update = null ) {
                return wfSetVar( $this->mForUpdate, $update );
        }

        /**
         * @param string $title Prefixed DB key
         * @return int Page ID or zero
         */
        public function getGoodLinkID( $title ) {
                $info = $this->mGoodLinks->get( $title );
                if ( !$info ) {
                        return 0;
                }
                return $info['id'];
        }

        /**
         * Get a field of a title object from cache.
         * If this link is not a cached good title, it will return NULL.
         * @param LinkTarget $target
         * @param string $field ('length','redirect','revision','model')
         * @return string|int|null
         */
        public function getGoodLinkFieldObj( LinkTarget $target, $field ) {
                $dbkey = $this->titleFormatter->getPrefixedDBkey( $target );
                $info = $this->mGoodLinks->get( $dbkey );
                if ( !$info ) {
                        return null;
                }
                return $info[$field];
        }

        /**
         * @param string $title Prefixed DB key
         * @return bool
         */
        public function isBadLink( $title ) {
                // Use get() to ensure it records as used for LRU.
                return $this->mBadLinks->get( $title ) !== false;
        }

        /**
         * Add a link for the title to the link cache
         *
         * @param int $id Page's ID
         * @param LinkTarget $target
         * @param int $len Text's length
         * @param int $redir Whether the page is a redirect
         * @param int $revision Latest revision's ID
         * @param string|null $model Latest revision's content model ID
         * @param string|null $lang Language code of the page, if not the content language
         */
        public function addGoodLinkObj( $id, LinkTarget $target, $len = -1, $redir = null,
                $revision = 0, $model = null, $lang = null
        ) {
                $dbkey = $this->titleFormatter->getPrefixedDBkey( $target );
                $this->mGoodLinks->set( $dbkey, [
                        'id' => (int)$id,
                        'length' => (int)$len,
                        'redirect' => (int)$redir,
                        'revision' => (int)$revision,
                        'model' => $model ? (string)$model : null,
                        'lang' => $lang ? (string)$lang : null,
                ] );
        }

        /**
         * Same as above with better interface.
         * @since 1.19
         * @param LinkTarget $target
         * @param stdClass $row Object which has the fields page_id, page_is_redirect,
         *  page_latest and page_content_model
         */
        public function addGoodLinkObjFromRow( LinkTarget $target, $row ) {
                $dbkey = $this->titleFormatter->getPrefixedDBkey( $target );
                $this->mGoodLinks->set( $dbkey, [
                        'id' => intval( $row->page_id ),
                        'length' => intval( $row->page_len ),
                        'redirect' => intval( $row->page_is_redirect ),
                        'revision' => intval( $row->page_latest ),
                        'model' => !empty( $row->page_content_model ) ? strval( $row->page_content_model ) : null,
                        'lang' => !empty( $row->page_lang ) ? strval( $row->page_lang ) : null,
                ] );
        }

        /**
         * @param LinkTarget $target
         */
        public function addBadLinkObj( LinkTarget $target ) {
                $dbkey = $this->titleFormatter->getPrefixedDBkey( $target );
                if ( !$this->isBadLink( $dbkey ) ) {
                        $this->mBadLinks->set( $dbkey, 1 );
                }
        }

        /**
         * @param string $title Prefixed DB key
         */
        public function clearBadLink( $title ) {
                $this->mBadLinks->delete( $title );
        }

        /**
         * @param LinkTarget $target
         */
        public function clearLink( LinkTarget $target ) {
                $dbkey = $this->titleFormatter->getPrefixedDBkey( $target );
                $this->mBadLinks->delete( $dbkey );
                $this->mGoodLinks->delete( $dbkey );
        }

        /**
         * Add a title to the link cache, return the page_id or zero if non-existent
         *
         * @deprecated since 1.27, unused
         * @param string $title Prefixed DB key
         * @return int Page ID or zero
         */
        public function addLink( $title ) {
                $nt = Title::newFromDBkey( $title );
                if ( !$nt ) {
                        return 0;
                }
                return $this->addLinkObj( $nt );
        }

        /**
         * Fields that LinkCache needs to select
         *
         * @since 1.28
         * @return array
         */
        public static function getSelectFields() {
                global $wgContentHandlerUseDB, $wgPageLanguageUseDB;

                $fields = [ 'page_id', 'page_len', 'page_is_redirect', 'page_latest' ];
                if ( $wgContentHandlerUseDB ) {
                        $fields[] = 'page_content_model';
                }
                if ( $wgPageLanguageUseDB ) {
                        $fields[] = 'page_lang';
                }

                return $fields;
        }

        /**
         * Add a title to the link cache, return the page_id or zero if non-existent
         *
         * @param LinkTarget $nt LinkTarget object to add
         * @return int Page ID or zero
         */
        public function addLinkObj( LinkTarget $nt ) {
                $key = $this->titleFormatter->getPrefixedDBkey( $nt );
                if ( $this->isBadLink( $key ) || $nt->isExternal()
                        || $nt->inNamespace( NS_SPECIAL )
                ) {
                        return 0;
                }
                $id = $this->getGoodLinkID( $key );
                if ( $id != 0 ) {
                        return $id;
                }

                if ( $key === '' ) {
                        return 0;
                }

                // Cache template/file pages as they are less often viewed but heavily used
                if ( $this->mForUpdate ) {
                        $row = $this->fetchPageRow( wfGetDB( DB_MASTER ), $nt );
                } elseif ( $this->isCacheable( $nt ) ) {
                        // These pages are often transcluded heavily, so cache them
                        $cache = $this->wanCache;
                        $row = $cache->getWithSetCallback(
                                $cache->makeKey( 'page', $nt->getNamespace(), sha1( $nt->getDBkey() ) ),
                                $cache::TTL_DAY,
                                function ( $curValue, &$ttl, array &$setOpts ) use ( $cache, $nt ) {
                                        $dbr = wfGetDB( DB_REPLICA );
                                        $setOpts += Database::getCacheSetOptions( $dbr );

                                        $row = $this->fetchPageRow( $dbr, $nt );
                                        $mtime = $row ? wfTimestamp( TS_UNIX, $row->page_touched ) : false;
                                        $ttl = $cache->adaptiveTTL( $mtime, $ttl );

                                        return $row;
                                }
                        );
                } else {
                        $row = $this->fetchPageRow( wfGetDB( DB_REPLICA ), $nt );
                }

                if ( $row ) {
                        $this->addGoodLinkObjFromRow( $nt, $row );
                        $id = intval( $row->page_id );
                } else {
                        $this->addBadLinkObj( $nt );
                        $id = 0;
                }

                return $id;
        }

        /**
         * @param WANObjectCache $cache
         * @param TitleValue $t
         * @return string[]
         * @since 1.28
         */
        public function getMutableCacheKeys( WANObjectCache $cache, TitleValue $t ) {
                if ( $this->isCacheable( $t ) ) {
                        return [ $cache->makeKey( 'page', $t->getNamespace(), sha1( $t->getDBkey() ) ) ];
                }

                return [];
        }

        private function isCacheable( LinkTarget $title ) {
                return ( $title->inNamespace( NS_TEMPLATE ) || $title->inNamespace( NS_FILE ) );
        }

        private function fetchPageRow( IDatabase $db, LinkTarget $nt ) {
                $fields = self::getSelectFields();
                if ( $this->isCacheable( $nt ) ) {
                        $fields[] = 'page_touched';
                }

                return $db->selectRow(
                        'page',
                        $fields,
                        [ 'page_namespace' => $nt->getNamespace(), 'page_title' => $nt->getDBkey() ],
                        __METHOD__
                );
        }

        /**
         * Purge the link cache for a title
         *
         * @param LinkTarget $title
         * @since 1.28
         */
        public function invalidateTitle( LinkTarget $title ) {
                if ( $this->isCacheable( $title ) ) {
                        $cache = ObjectCache::getMainWANInstance();
                        $cache->delete(
                                $cache->makeKey( 'page', $title->getNamespace(), sha1( $title->getDBkey() ) )
                        );
                }
        }

        /**
         * Clears cache
         */
        public function clear() {
                $this->mGoodLinks->clear();
                $this->mBadLinks->clear();
        }
}