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Caching and tuning fun for high scalability
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Caching and tuning fun for high scalability

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Caching has been a 'hot' topic for a few years. But caching takes more than merely taking data and putting it in a cache : the right caching techniques can improve performance and reduce load ...

Caching has been a 'hot' topic for a few years. But caching takes more than merely taking data and putting it in a cache : the right caching techniques can improve performance and reduce load significantly. But we'll also look at some major pitfalls, showing that caching the wrong way can bring down your site. If you're looking for a clear explanation about various caching techniques and tools like Memcached, Nginx and Varnish, as well as ways to deploy them in an efficient way, this talk is for you.

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Caching and tuning fun for high scalability Caching and tuning fun for high scalability Presentation Transcript

  • Caching and tuning funfor high scalabilityWim GoddenCu.be Solutions
  • Who am I ?Wim Godden (@wimgtr)Founder of Cu.be Solutions (http://cu.be)Open Source developer since 1997Developer of OpenXZend Certified EngineerZend Framework Certified EngineerMySQL Certified Developer
  • Who are you ?Developers ?System/network engineers ?Managers ?Caching experience ?
  • Goals of this tutorialEverything about caching and tuningA few techniquesHow-toHow-NOT-to→ Increase reliability, performance and scalability5 visitors/day → 5 million visitors/day(Dont expect miracle cure !)
  • LAMP
  • Architecture
  • Test page3 DB-queriesselect firstname, lastname, email from user where user_id = 5;select title, createddate, body from article order by createddate desc limit 5;select title, createddate, body from article order by score desc limit 5;Page just outputs result
  • Our base benchmarkApachebench = useful enoughResult ?Single webserver ProxyStatic PHP Static PHPApache + PHP 3900 17.5 6700 17.5Limit :CPU, networkor diskLimit :database
  • CachingCaching
  • What is caching ?CACHECACHE
  • What is caching ?x = 5, y = 2n = 50Same resultCACHECACHEselect*fromarticlejoin useron article.user_id = user.idorder bycreated desclimit10Doesnt changeall the time
  • Theory of cachingDBCache$data = get(key)falseGET /pagePageselect data fromtable$data = returned resultset(key, $data)if ($data == false)
  • Theory of cachingDBCacheHIT
  • Caching techniques#1 : Store entire pages#2 : Store part of a page (block)#3 : Store data retrieval (SQL ?)#4 : Store complex processing result#? : Your call !When you have data, think :Creating time ?Modification frequency ?Retrieval frequency ?
  • How to find cacheable dataNew projects : start from cache everythingExisting projects :Look at MySQL slow query logMake a complete query log (dont forget to turn it off !)→ Use Percona Toolkit (pt-query-digest)Check page loading times
  • Caching storage - DiskData with few updates : goodCaching SQL queries : preferably notDONT use NFS or other network file systemshigh latencypossible problem for sessions : locking issues !
  • Caching storage - Disk / ramdiskLocal5 Webservers → 5 local cachesHow will you keep them synchronized ?→ Dont say NFS or rsync !
  • Caching storage - Memcache(d)Facebook, Twitter, YouTube, … → need we say more ?Distributed memory caching systemMultiple machines ↔ 1 big memory-based hash-tableKey-value storage systemKeys - max. 250bytesValues - max. 1Mbyte
  • Caching storage - Memcache(d)Facebook, Twitter, YouTube, … → need we say more ?Distributed memory caching systemKey-value storage systemKeys - max. 250bytesValues - max. 1MbyteExtremely fast... non-blocking, UDP (!)
  • Memcache - where to install
  • Memcache - where to install
  • Memcache - installation & running itInstallationDistribution packagePECLWindows : binariesRunningNo config-filesmemcached -d -m <mem> -l <ip> -p <port>ex. : memcached -d -m 2048 -l 172.16.1.91 -p 11211
  • Caching storage - Memcache - some notesNot fault-tolerantIts a cache !Lose session dataLose shopping cart data...
  • Caching storage - Memcache - some notesNot fault-tolerantIts a cache !Lose session dataLose shopping cart data…Firewall your Memcache port !
  • Memcache in code<?php$memcache = new Memcache();$memcache->addServer(172.16.0.1, 11211);$memcache->addServer(172.16.0.2, 11211);$myData = $memcache->get(myKey);if ($myData === false) {$myData = GetMyDataFromDB();// Put it in Memcache as myKey, without compression, with no expiration$memcache->set(myKey, $myData, false, 0);}echo $myData;
  • Benchmark with MemcacheSingle webserver ProxyStatic PHP Static PHPApache + PHP 3900 17.5 6700 17.5Apache + PHP + MC 3900 55 6700 108
  • Memcache slabs(or why Memcache says its full when its not)Multiple slabs of different sizes :Slab 1 : 400 bytesSlab 2 : 480 bytes (400 * 1.2)Slab 3 : 576 bytes (480 * 1.2) (and so on...)Multiplier (1.2 here) can be configuredStore a lot of very large objects→ Large slabs : full→ Rest : free→ Eviction of data !
  • Memcache - Is it working ?Connect to it using telnet"stats" command →Use Cacti or other monitoring toolsSTAT pid 2941STAT uptime 10878STAT time 1296074240STAT version 1.4.5STAT pointer_size 64STAT rusage_user 20.089945STAT rusage_system 58.499106STAT curr_connections 16STAT total_connections 276950STAT connection_structures 96STAT cmd_get 276931STAT cmd_set 584148STAT cmd_flush 0STAT get_hits 211106STAT get_misses 65825STAT delete_misses 101STAT delete_hits 276829STAT incr_misses 0STAT incr_hits 0STAT decr_misses 0STAT decr_hits 0STAT cas_misses 0STAT cas_hits 0STAT cas_badval 0STAT auth_cmds 0STAT auth_errors 0STAT bytes_read 613193860STAT bytes_written 553991373STAT limit_maxbytes 268435456STAT accepting_conns 1STAT listen_disabled_num 0STAT threads 4STAT conn_yields 0STAT bytes 20418140STAT curr_items 65826STAT total_items 553856STAT evictions 0STAT reclaimed 0
  • Memcache - backing up
  • Memcache - tipPage with multiple blocks ?→ use Memcached::getMulti()But : what if you get some hits and some misses ?getMulti($array)Hashingalgorithm
  • Updating data
  • Updating dataLCD_Popular_Product_List
  • Adding/updating data$memcache->delete(LCD_Popular_Product_List);
  • Adding/updating data
  • Adding/updating data - Why it crashed
  • Adding/updating data - Why it crashed
  • Adding/updating data - Why it crashed
  • Cache stampeding
  • Cache stampeding
  • Memcache code ?DBVisitor interface Admin interfaceMemcache code
  • Cache warmup scriptsUsed to fill your cache when its emptyRun it before starting Webserver !2 ways :Visit all URLsError-proneHard to maintainCall all cache-updating methodsMake sure you have a warmup script !
  • Cache stampeding - what about locking ?Seems like a nice idea, but...While lock in placeWhat if the process that created the lock fails ?
  • LAMP...→ LAMMP→ LNMMP
  • NginxWeb serverReverse proxyLightweight, fast12.81% of all Websites
  • NginxNo threads, event-drivenUses epoll / kqueueLow memory footprint10000 active connections = normal
  • Nginx - Configurationserver {listen 80;server_name www.domain.ext *.domain.ext;index index.html;root /home/domain.ext/www;}server {listen 80;server_name photo.domain.ext;index index.html;root /home/domain.ext/photo;}
  • Nginx with PHP-FPMSince PHP 5.3.3Runs on port 9000Nginx connects using fastcgi methodlocation / {fastcgi_pass 127.0.0.1:9000;fastcgi_index index.php;include fastcgi_params;fastcgi_param SCRIPT_NAME $fastcgi_script_name;fastcgi_param SCRIPT_FILENAME /home/www.4developers.pl/$fastcgi_script_name;fastcgi_param SERVER_NAME $host;fastcgi_intercept_errors on;}
  • Nginx + PHP-FPM featuresGraceful upgradeSpawn new processes under high loadChrootSlow request log !
  • Nginx + PHP-FPM featuresGraceful upgradeSpawn new processes under high loadChrootSlow request log !fastcgi_finish_request() → offline processing
  • Nginx + PHP-FPM - performance ?Single webserver ProxyStatic PHP Static PHPApache + PHP 3900 17.5 6700 17.5Apache + PHP + MC 3900 55 6700 108Nginx + PHP-FPM + MC 11700 57 11200 112Limit :single-threadedApachebench
  • Nginx + PHP-FPM - performance ?Single webserver ProxyStatic PHP Static PHPApache + PHP 3900 17.5 6700 17.5Apache + PHP + MC 3900 55 6700 108Apache (tuned) + PHP/MC 10600 55 11400 108Nginx + PHP-FPM + MC 11700 57 11200 112Limit :single-threadedApachebench
  • Reverse proxy time...
  • VarnishNot just a load balancerReverse proxy cache / http accelerator / …Caches (parts of) pages in memoryCareful :uses threads (like Apache)Nginx usually scales better (but doesnt have VCL)
  • Varnish - backends + load balancingbackend server1 {.host = "192.168.0.10";}backend server2 {.host = "192.168.0.11";}director example_director round-robin {{.backend = server1;}{.backend = server2;}}
  • Varnish - VCLVarnish Configuration LanguageDSL (Domain Specific Language)→ compiled to CHooks into each requestDefines :Backends (web servers)ACLsLoad balancing strategyCan be reloaded while running
  • Varnish - whatever you wantReal-time statistics (varnishtop, varnishhist, ...)ESI
  • Article content pageArticle content (TTL : 15 min)/article/732Varnish - ESIPerfect for caching pagesHeader (TTL : 60 min)/topLatest news (TTL : 2 min) /newsNavigation(TTL :60 min)/navIn your article page output :<esi:include src="/top"/><esi:include src="/nav"/><esi:include src="/news"/><esi:include src="/article/732"/>In your Varnish config :sub vcl_fetch {if (req.url == "/news") {esi; /* Do ESI processing */set obj.ttl = 2m;} elseif (req.url == "/nav") {esi;set obj.ttl = 1m;} elseif ….….}
  • Varnish with ESI - hold on tight !Single webserver ProxyStatic PHP Static PHPApache + PHP 3900 17.5 6700 17.5Apache + PHP + MC 3900 55 6700 108Nginx + PHP-FPM + MC 11700 57 11200 112Varnish - - 11200 4200
  • Varnish - what can/cant be cached ?Can :Static pagesImages, js, cssPages or parts of pages that dont change often (ESI)Cant :POST requestsVery large files (its not a file server !)Requests with Set-CookieUser-specific content
  • ESI → no caching on user-specific content ?Logged in as : Wim Godden5 messagesTTL = 5minTTL=1hTTL = 0s ?
  • Coming soon...Based on NginxReduces load by 50 – 95%Requires code changes !Well-built project → few changesEffect on webservers and database servers
  • Whats the result ?
  • Whats the result ?
  • FiguresSecond customer (already using Nginx + Memcache) :No. of web servers : 72 → 8No. of db servers : 15 → 4Total : 87 → 12 (86% reduction !)Latest customer :Total no. of servers : 1350 → 38072% reduction → €1.5 million / year
  • AvailabilityOld system : stable at 4 customersTotal rebuild : still under heavy developmentBeta : Sep 2013Final : End 2013
  • PHP speed - some tipsUpgrade PHP - every minor release has 5-15% speed gain !Use an opcode cache (APC, eAccelerator, XCache)
  • DB speed - some tipsUse same types for joinsi.e. dont join decimal with intRAND() is evil !count(*) is evil in InnoDB without a where clause !Persistent connect is sort-of evil
  • Caching & Tuning @ frontendhttp://www.websiteoptimization.com/speed/tweak/average-web-page/
  • Frontend tuning1. You optimize backend2. Frontend engineers messes up → havoc on backend3. Dont forget : frontend sends requests to backend !SO...Care about frontendTest frontendCheck what requests frontend sends to backend
  • Tuning frontendMinimize requestsCombine CSS/JavaScript files
  • Tuning frontendMinimize requestsCombine CSS/JavaScript filesUse CSS Sprites
  • CSS Sprites
  • Tuning content - CSS sprites
  • Tuning content - CSS sprites11 images11 HTTP requests24KByte1 image1 HTTP requests14KByte
  • Tuning frontendMinimize requestsCombine CSS/JavaScript filesUse CSS Sprites (horizontally if possible)Put CSS at topPut JavaScript at bottomMax. no connectionsEspecially if JavaScript does Ajax (advertising-scripts, …) !Avoid iFramesAgain : max no. of connectionsDont scale images in HTMLHave a favicon.ico (dont 404 it !)→ see my blog
  • What else can kill your site ?Redirect loopsMultiple requestsMore load on WebserverMore PHP to processAdditional latency for visitorTry to avoid redirects anyway→ In ZF : use $this->_forward instead of $this->_redirectWatch your logs, but equally important...Watch the logging process →Logging = disk I/O → can kill your server !
  • Above all else... be prepared !Have a monitoring systemUse a cache abstraction layer (disk → Memcache)Dont install for the worst → prepare for the worstHave a test-setupHave fallbacks→ Turn off non-critical functionality
  • So...CacheBut : never delete, always push !Have a warmup scriptMonitor your cacheHave an abstraction layerApache = fine, Nginx = betterStatic pages ? Use VarnishTune your frontend → impact on backend !
  • Questions ?
  • Questions ?
  • ContactTwitter @wimgtrWeb http://techblog.wimgodden.beSlides http://www.slideshare.net/wimgE-mail wim.godden@cu.bePlease...Rate my talk : http://joind.in/8228
  • Thanks !Please...Rate my talk : http://joind.in/8228