cache rules everything around me
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CACHE RULESEVERYTHINGAROUND ME
presented atWordCamp Baltimore
September 21 2013
HI, I'M RUSSELL HEIMLICH(Heimlich, like the maneuver)
Head Cache Invalidator at the Pew Research Center
BUT FIRST ASTORY…
MONTHS OF WORK GO IN TO THERELEASE OF NEW RANKINGS.
ON LAUNCH DAY WEALWAYS SEE A HUGE
TRAFFIC SPIKEBut one year we got lucky…
The marketing/biz dev team managed to get us featured onthe homepage of a major web portal!
(And by featured I mean the featured story on their homepage)
WE WERE GOING TO BEFEATURED ON…
(Before their CEO discovered Adobe Illustrator)
WE WERE EXCITED!
Ok maybe we looked more like this…
The story went live on Yahoo.com and we watched…
The servers started getting slower…
Editors were calling us saying they couldn't get in to theadmin area…
Our servers were completely down…
We had to call Yahoo! and have them remove the storybecause we couldn't handle the traffic…
WE LASTED 15 MINUTES.
PERFORMANCE AND UPTIMEARE IMPORTANT!
And caching can help.
WHAT ISCACHING?
CACHE“a component that transparently stores dataso that future requests for that data can be
served faster.”
— via Wikipedia, Cache (Computing)
A cache may contain values computed earlier or duplicatevalues stored elsewhere.
A cache hit can complete the request by reading the valuefrom the cache.
A cache miss has to be recomputed or fetched fromanother location which is much slower.
The more requests that can be served from a cache, thefaster the system performs.
The faster the system, the more requests it can handle.
A REAL-WORLD EXAMPLEYou're taking 5 classes and need to write 5 essays…
You could write 5 separate essays
ORYou could write one essay and use it for all of your classes
THAT'S CACHING!
There are many (potential) layers of caching involved in asingle web request.
HOW DOES AREQUESTWORK?
A BASIC REQUEST
A BASIC REQUEST
PHP PAGESTAKE LONGERTO SERVE
A PHP PAGE REQUEST
A PHP PAGE REQUEST
A PHP PAGEWITH MYSQLDATA TAKESEVEN MOREWORK
A PHP/MYSQL PAGEREQUEST
A PHP/MYSQL PAGEREQUEST
WE WANT TO MINIMIZE THEAMOUNT OF WORK DONEBY OUR SERVER, PHP AND
MYSQL
HTTP HEADERS
“The easiest request to serve is the one neversent at all.”
I just made this quote up.
Your logo image isn't going to change when going from yourhomepage to a single blog post…
So why make the browser even request it?
FAR FUTURE EXPIRESHEADER
Tell the browser how long the copy of the file is validCached files that are valid are not re-downloaded fromthe server
WHAT DOES THAT LOOKLIKE?
Add this to your file:.htaccess
<ifmodule mod_expires.c="">
ExpiresActive on ExpiresDefault "access plus 1 month"
ExpiresByType image/gif "access plus 1 month" ExpiresByType image/jpeg "access plus 1 month" ExpiresByType image/png "access plus 1 month"
</ifmodule>
The HTML5 Boiler Plate project's .htaccess file
Read the docsView the source
BUT WHAT IF THEIMAGE/JS/CSS FILE
CHANGES?The browser will keep loading the resource from it's local
cache
>
And then you have to clear the browser cache or hardrefresh the page (Shift + Refresh).
WE NEED CACHE-BUSTINGFILENAMES!
WordPress' and supports this
wp_enqeue_script() wp_enqueue_style()
wp_enqueue_script( $handle, $src, $deps, $ver, $in_footer );wp_enqueue_style( $handle, $src, $deps, $ver, $media );
which outputs a script like this
my-super-neato-script.js?ver=3.6.1my-trendy-styles.css?ver=3.6.1
But then every time you update your JavaScript or CSS youneed to change the $ver variable to bust the cache…
SO I WROTE A PLUGINCDN Friendly CSS and JS URLs in WordPress
/theme/css/2013-09-12_5:21/my-style.css
maps to
/theme/css/my-style.css
CDNS
CONTENT DELIVERYNETWORKS (CDNS)
Set of servers in multiple data centers around the world toserve content with high availability and performance.
CDNs serve their copy of a file, if available, sparing yourserver from the traffic.
If the CDN doesn't have a copy of the file, it passes therequest back to the origin.
TWO TYPES OF CDNS1. Push - assets get uploaded to the CDN manually, you link
directly to it2. Pull - The CDN is a proxy saving requests that are passed
through itSee Push vs. Pull CDNs
DNS CHANGES NEEDED FORPULL CDNS
cdn.example.com masks ugly CDN URL (CNAME)
DNS CHANGES NEEDED FORPULL CDNS
example.com points to origin IP Address (A Record)
The CDN uses the Expires header to determine if cachedasset is stale or not.
Stale requests get passed to the origin server
Some CDNs and proxies . So avoid it if you can.
don't cache URLs with a querystring
BADhttp://www.example.com/js/file.js?2013-09-12
GOODhttp://www.example.com/js/2013-09-12/file.jshttp://www.example.com/js/file.2013-09-12.js
If you cache your HTML via a CDN then if your origin servergoes down your site will still be served. Visitors won't even
know.
Distributing content across the world, visitors will downloadfrom a server closer to them.
CDN PROVIDERSAkamaiEdgeCastAmazon CloudfrontMaxCDNCloudFlare
FULL PAGECACHING
Full page caching takes the result of a page request fromWordPress and saves it as a static HTML file that will be
served up the next time.
This reduces the load on PHP and MySQL
CACHING PLUGINS (Advandced, lots of options) (Easier set-up)
(Multi-server environment) (For low-resource hosts)
W3 Total CacheWP Super CacheBatcacheHyper Cache
CACHING PLUGIN TIPSDon't cache pages for logged in usersDon't cache POST requestsDo serve cached files from mod_rewrite (not PHP)Don't serve a separate mobile version (use responsivedesign)Make sure it is working!
PHP CACHING
WORDPRESS' CACHING APISTransients APIWP Object Cache
TRANSIENTS APIUsed to store data that can expire at any timeHas an expiration to invalidate the dataUses the wp_options table or an object cache
See http://codex.wordpress.org/Transients_API
TRANSIENTS APIFUNCTIONS
set_transient()get_transient()delete_transient()
MULTISITE TRANSIENTS APIFUNCTIONS
set_site_transient()get_site_transient()delete_site_transient()
TRANSIENTS EXAMPLE$my_transient = get_transient( 'my_transient' );if( $my_transient == false ) { //Do some complicated task worth caching $my_transient = 'Something complicated'; set_transient( 'my_transient', $my_transient, 12 * HOUR_IN_SECONDS );}
TIME CONSTANTSAs of WordPress 3.5 several constants were introduced to
easily express time
MINUTE_IN_SECONDS = 60 (seconds)HOUR_IN_SECONDS = 60 * MINUTE_IN_SECONDSDAY_IN_SECONDS = 24 * HOUR_IN_SECONDSWEEK_IN_SECONDS = 7 * DAY_IN_SECONDSYEAR_IN_SECONDS = 365 * DAY_IN_SECONDS
TRANSIENTS API IS IDEALFOR…
Fetching RSS feedsStoring an external API callCaching a complex queryANYTHING that needs to expire at some time
WP OBJECT CACHEWordPress' internal class for caching data.
See http://codex.wordpress.org/Class_Reference/WP_Object_Cache
CACHING PERSISTANCEWP_Object_Cache data isn't saved between page requests
by default.If an object cache is available, WP_Object_Cache will use that
instead
WP_CACHE FUNCTIONSDon't call WP_Object_Cache Class directly!
wp_cache_add( $key, $data, $group, $expire );wp_cache_set( $key, $data, $group, $expire );wp_cache_get( $key, $group = '', $force = false, $found = null );wp_cache_delete( $key, $group );wp_cache_replace( $key, $data, $group, $expire )
WHEN SHOULD WE USETHIS?
OBJECTCACHING
WHAT IS OBJECT CACHING?Distributed, in-memory key-value store for
small chunks of data.
(not distributed)
MemcachedRedisAPC
UH… IN ENGLISH?Store Transients API and WP Object Cache items inmemory between requestsMake it available to multiple serversRAM is way faster than disk!
HOW DO I ENABLE OBJETCACHING?
1. Download and install or or onyour server
2. Add the appropriate object-cache.php file to your wp-content folder
Memcached Redis APC
See: or
orMemcached Object Cache PluginWordPress Redis BackendAPC Object Cache Backend
OPCODECACHING
WHAT DOES OPCODECACHING DO?
PHP is written in a human-readable syntaxWhen run, PHP is compiled to opcode that a computerunderstandsAn opcode cache speeds up the execution of PHP
OPCODE CACHESAlternative PHP Cache (APC)eAcceleratorXCacheZend Optimizer+
WHICH OPCODE CACHE TOUSE?
Zend Optimizer+ will be bundled with PHP 5.5
See http://halfelf.org/2013/trading-apc-for-zend/
BENCHMARKSPHP (No Opcode Cache) ~40APC ~260Zend Optimizer + ~307
Number of Requests per second
See http://www.ricardclau.com/2013/03/apc-vs-zend-optimizer-benchmarks-with-symfony2/
MYSQLCACHING
MYSQL'S QUERY CACHECache's result for frequently used SELECT statementsAny INSERT, UPDATE, or DELETE statement flushes thequery cache
See MySQL Query Cache Documentation
TO SUMMARIZE
Leverage browser caching via HTTP headersUse a CDN if you can or a full-page caching pluginWordPress' caching APIs are helpfulSet-up object caching on your serverUtilize an opcode cache to speed up PHPMake sure MySQL's query_cache is turned on
MORE READING1. by Zack Tollman2. by Joseph Scott3. by Ryan
Burnette4. by WordPress.com VIP5.
by Erick Hitter6. by Scott Taylor
Core Caching Concepts in WordPressScaling WordPressWordPress Fragment Caching Revisited
CachingCaching, Scaling, and What I've Learned Programmingfor WordPress.com VIPWordPress + Memcached
INCONCLUSION
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