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diff --git a/docs/memcached.txt b/docs/memcached.txt new file mode 100644 index 00000000..6752e9c8 --- /dev/null +++ b/docs/memcached.txt @@ -0,0 +1,132 @@ +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/ + +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 == + +* 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 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. +********************* W A R N I N G ! ! ! ! ! *********************** + +== Setup == + +If you want to start small, just run one memcached on your web +server: + + memcached -d -l 127.0.0.1 -p 11000 -m 64 + +(to run in daemon mode, accessible only via loopback interface, +on port 11000, using up to 64MB of memory) + +In your LocalSettings.php file, set: + + $wgUseMemCached = true; + $wgMemCachedServers = array( "127.0.0.1:11000" ); + +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( + "127.0.0.1:11000", # one gig on this box + array("192.168.0.1:11000", 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 + +If you don't set $wgUseMemCached, we 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. + +== 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() + +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() + cleared by: nothing + +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() + +... more to come ... |