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Diffstat (limited to 'www/wiki/docs/memcached.txt')
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diff --git a/www/wiki/docs/memcached.txt b/www/wiki/docs/memcached.txt new file mode 100644 index 00000000..8c59e72d --- /dev/null +++ b/www/wiki/docs/memcached.txt @@ -0,0 +1,235 @@ +MediaWiki has optional support for memcached, a "high-performance, +distributed memory object caching system". For general information +on it, see: http://www.danga.com/memcached/ + +Memcached is likely more trouble than a small site will need, but +for a larger site with heavy load, like Wikipedia, it should help +lighten the load on the database servers by caching data and objects +in memory. + +== Installation == + +Packages are available for Fedora, Debian, Ubuntu and probably other +Linux distributions. If there's no package available for your +distribution, you can compile it from source. + +== Compilation == + +* PHP must be compiled with --enable-sockets + +* libevent: http://www.monkey.org/~provos/libevent/ + (as of 2003-08-11, 0.7a is current) + +* optionally, epoll-rt patch for Linux kernel: + http://www.xmailserver.org/linux-patches/nio-improve.html + +* memcached: http://www.danga.com/memcached/download.bml + (as of this writing, 1.1.9 is current) + +Memcached and libevent are under BSD-style licenses. + +The server should run on Linux and other Unix-like systems... you +can run multiple servers on one machine or on multiple machines on +a network; storage can be distributed across multiple servers, and +multiple web servers can use the same cache cluster. + +********************* W A R N I N G ! ! ! ! ! *********************** +Memcached has no security or authentication. Please ensure that your +server is appropriately firewalled, and that the port(s) used for +memcached servers are not publicly accessible. Otherwise, anyone on +the internet can put data into and read data from your cache. + +An attacker familiar with MediaWiki internals could use this to steal +passwords and email addresses, or to make themselves a sysop and +install malicious javascript on the site. There may be other types +of vulnerability, no audit has been done -- so be safe and keep it +behind a firewall. +********************* W A R N I N G ! ! ! ! ! *********************** + +== Setup == + +If you installed memcached using a distro, the daemon should be started +automatically using /etc/init.d/memcached. + +To start the daemon manually, use something like: + + memcached -d -l 127.0.0.1 -p 11211 -m 64 + +(to run in daemon mode, accessible only via loopback interface, +on port 11211, using up to 64MB of memory) + +In your LocalSettings.php file, set: + + $wgMainCacheType = CACHE_MEMCACHED; + $wgMemCachedServers = array( "127.0.0.1:11211" ); + +The wiki should then use memcached to cache various data. To use +multiple servers (physically separate boxes or multiple caches +on one machine on a large-memory x86 box), just add more items +to the array. To increase the weight of a server (say, because +it has twice the memory of the others and you want to spread +usage evenly), make its entry a subarray: + + $wgMemCachedServers = array( + "127.0.0.1:11211", # one gig on this box + array("192.168.0.1:11211", 2 ) # two gigs on the other box + ); + +== PHP client for memcached == + +MediaWiki uses a fork of Ryan T. Dean's pure-PHP memcached client. +It also supports the PECL PHP extension for memcached. + +MediaWiki uses three object for object caching: +* $wgMemc, controlled by $wgMainCacheType +* $parserMemc, controlled by $wgParserCacheType +* $messageMemc, controlled by $wgMessageCacheType +If you set CACHE_NONE to one of the three control variable, (default +value for $wgMainCacheType), MediaWiki still create a MemCacheClient, +but requests to it are no-ops and we always fall through to the +database. If the cache daemon can't be contacted, it should also +disable itself fairly smoothly. + +By default, $wgMemc is used but when it is $parserMemc or $messageMemc +this is mentioned below. + +== Keys used == + +(incomplete, out of date) + +Date Formatter: + key: $wgDBname:dateformatter + ex: wikidb:dateformatter + stores: a single instance of the DateFormatter class + cleared by: nothing + expiry: one hour + +Difference Engine: + key: $wgDBname:diff:version:{MW_DIFF_VERSION}:oldid:$old:newid:$new + ex: wikidb:diff:version:1.11a:oldid:1:newid:2 + stores: body of a difference + cleared by: nothing + expiry: one week + +Interwiki: + key: $wgDBname:interwiki:$prefix + ex: wikidb:interwiki:w + stores: object from the interwiki table of the database + expiry: $wgInterwikiExpiry + cleared by: nothing + +Lag time of the databases: + key: $wgDBname:lag_times + ex: wikidb:lag_times + stores: array mapping the database id to its lag time + expiry: 5 secondes + cleared by: nothing + +Localisation: + key: $wgDBname:localisation:$lang + ex: wikidb:localisation:de + stores: array of localisation settings + set in: Language::loadLocalisation() + expiry: none + cleared by: Language::loadLocalisation() + +Message Cache: + stored in: $messageMemc + key: $wgDBname:messages, $wgDBname:messages-hash, $wgDBname:messages-status + ex: wikidb:messages, wikidb:messages-hash, wikidb:messages-status + stores: an array where the keys are DB keys and the values are messages + set in: wfMessage(), Article::editUpdates() and Title::moveTo() + expiry: $wgMsgCacheExpiry + cleared by: nothing + +Newtalk: + key: $wgDBname:newtalk:ip:$ip + ex: wikidb:newtalk:ip:123.45.67.89 + stores: integer, 0 or 1 + set in: User::loadFromDatabase() + cleared by: User::saveSettings() # ? + expiry: 30 minutes + +Parser Cache: + stored in: $parserMemc + key: $wgDBname:pcache:idhash:$pageid-$renderkey!$hash + $pageid: id of the page + $renderkey: 1 if action=render, 0 otherwise + $hash: hash of user options applied to the page, see ParserOptions::optionsHash() + ex: wikidb:pcache:idhash:1-0!1!0!!en!2 + stores: ParserOutput object + modified by: WikiPage::doEditUpdates() or PoolWorkArticleView::doWork() + expiry: $wgParserCacheExpireTime or less if it contains short lived functions + + key: $wgDBname:pcache:idoptions:$pageid + stores: CacheTime object with an additional list of used options for the hash, + serves as ParserCache pointer. + modified by: ParserCache::save() + expiry: The same as the ParserCache entry it points to. + +Ping limiter: + controlled by: $wgRateLimits + key: $wgDBname:limiter:action:$action:ip:$ip, + $wgDBname:limiter:action:$action:user:$id, + mediawiki:limiter:action:$action:ip:$ip and + mediawiki:limiter:action:$action:subnet:$sub + ex: wikidb:limiter:action:edit:ip:123.45.67.89, + wikidb:limiter:action:edit:user:1012 + mediawiki:limiter:action:edit:ip:123.45.67.89 and + mediawiki:limiter:action:$action:subnet:123.45.67 + stores: number of action made by user/ip/subnet + cleared by: nothing + expiry: expiry set for the action and group in $wgRateLimits + + +Proxy Check: (deprecated) + key: $wgDBname:proxy:ip:$ip + ex: wikidb:proxy:ip:123.45.67.89 + stores: 1 if the ip is a proxy + cleared by: nothing + expiry: $wgProxyMemcExpiry + +Revision text: + key: $wgDBname:revisiontext:textid:$id + ex: wikidb:revisiontext:textid:1012 + stores: text of a revision + cleared by: nothing + expiry: $wgRevisionCacheExpiry + +Sessions: + controlled by: $wgSessionsInObjectCache + key: $wgBDname:session:$id + ex: wikidb:session:38d7c5b8d3bfc51egf40c69bc40f8be3 + stores: $SESSION, useful when using a multi-sever wiki + expiry: one hour + cleared by: session_destroy() + +Sidebar: + stored in: $parserMemc + controlled by: $wgEnableSidebarCache + key: $wgDBname:sidebar + ex: wikidb:sidebar + stores: the html output of the sidebar + expiry: $wgSidebarCacheExpiry + cleared by: MessageCache::replace() + +Special:Allpages: + key: $wgDBname:allpages:ns:$ns + ex: wikidb:allpages:ns:0 + stores: array of pages in a namespace + expiry: one hour + cleared by: nothing + +Special:Recentchanges (feed): + stored in: $messageMemc + key: $wgDBname:rcfeed:$format:$limit:$hideminor:$target and + rcfeed:$format:timestamp + ex: wikidb:rcfeed:rss:50:: and rcfeed:rss:timestamp + stores: xml output of feed + expiry: one day + clear by: maintenance/rebuildrecentchanges.php script, or + calling Special:Recentchanges?action=purge&feed=rss, + Special:Recentchanges?action=purge&feed=atom, + but note need $wgGroupPermissions[...]['purge'] permission. + +... more to come ... |