-memcached support for MediaWiki:
-
-From ca August 2003, 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/
+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.
-== Requirements ==
+== Installation ==
+
+Packages are available for Fedora, Debian, Ubuntu and probably other
+Linux distributions. If you there's no package available for your
+distribution, you can compile it from source.
+
+== Compilation ==
* PHP must be compiled with --enable-sockets
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 give
-themselves developer access and delete all data from the wiki's
-database, as well as getting all users' password hashes and e-mail
-addresses.
+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 want to start small, just run one memcached on your web
-server:
+If you installed memcached using a distro, the daemon should be started
+automatically using /etc/init.d/memcached.
- memcached -d -l 127.0.0.1 -p 11000 -m 64
+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 11000, using up to 64MB of memory)
+on port 11211, using up to 64MB of memory)
In your LocalSettings.php file, set:
- $wgMainCacheType = CACHE_MEMCACHED;;
- $wgMemCachedServers = array( "127.0.0.1:11000" );
+ $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
usage evenly), make its entry a subarray:
$wgMemCachedServers = array(
- "127.0.0.1:11000", # one gig on this box
- array("192.168.0.1:11000", 2 ) # two gigs on the other box
+ "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 ==
-As of this writing, MediaWiki includes version 1.0.10 of the PHP
-memcached client by Ryan Gilfether <hotrodder@rocketmail.com>.
-You'll find some documentation for it in the 'php-memcached'
-subdirectory under the present one.
-
-We intend to track updates, but if you want to check for the lastest
-released version, see http://www.danga.com/memcached/apis.bml
+MediaWiki uses a fork of Ryan T. Dean's pure-PHP memcached client.
+The newer PECL module is not yet supported.
-If you don't set $wgUseMemCached, we still create a MemCacheClient,
+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 mentionned below.
+
== Keys used ==
-User:
- key: $wgDBname:user:id:$sId
- ex: wikidb:user:id:51
- stores: instance of class User
- set in: User::loadFromSession()
- cleared by: User::saveSettings(), UserTalkUpdate::doUpdate()
-
+(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
+ expriy: 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: wfMsg(), Article::editUpdates() both call wfLoadAllMessages()
+ expriy: $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 set to 30 minutes
-
-LinkCache:
- key: $wgDBname:lc:title:$title
- ex: wikidb:lc:title:Wikipedia:Welcome,_Newcomers!
- stores: cur_id of page, or 0 if page does not exist
- set in: LinkCache::addLink()
- cleared by: LinkCache::clearBadLink()
- should be cleared on page deletion and rename
-MediaWiki namespace:
- key: $wgDBname:messages
- ex: wikidb:messages
- stores: an array where the keys are DB keys and the values are messages
- set in: wfMsg(), Article::editUpdates() both call wfLoadAllMessages()
+ expiry: 30 minutes
+
+Parser Cache:
+ stored in: $parserMemc
+ controlled by: $wgEnableParserCache
+ 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: Article::editUpdates() or Article::getOutputFromWikitext()
+ 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
+ expriry: $wgRevisionCacheExpiry
+
+Sessions:
+ controlled by: $wgSessionsInMemcached
+ key: $wgBDname:session:$id
+ ex: wikidb:session:38d7c5b8d3bfc51egf40c69bc40f8be3
+ stores: $SESSION, useful when using a multi-sever wiki
+ expriy: 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
+ expriy: $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.
+
+Statistics:
+ controlled by: $wgStatsMethod
+ key: $wgDBname:stats:$key
+ ex: wikibd:stats:request_with_session
+ stores: counter for statistics (see maintenance/stats.php script)
+ expiry: none (?)
+ cleared by: maintenance/clear_stats.php script
-Watchlist:
- key: $wgDBname:watchlist:id:$userID
- ex: wikidb:watchlist:id:4635
- stores: HTML string
- cleared by: nothing, expiry time $wgWLCacheTimeout (1 hour)
- note: emergency optimisation only
-
-IP blocks:
- key: $wgDBname:ipblocks
- ex: wikidb:ipblocks
- stores: array of arrays, for the BlockCache class
- cleared by: BlockCache:clear()
+User:
+ key: $wgDBname:user:id:$sId
+ ex: wikidb:user:id:51
+ stores: instance of class User
+ set in: User::saveToCache()
+ cleared by: User::saveSettings(), User::clearSharedCache()
-... more to come ...
\ No newline at end of file
+... more to come ...