WordCamp San Francisco 2011: Transients, Caching, and the Complexities of Multisite

The Otto & Nacin ShowWordCamp San Francisco 2011August 12, 2011

Nacin OttoContributing Developers to WordPress Tech Ninjas at Audrey Capitalnacin@wordpress.org otto@wordpress.org@nacin @otto42

Transients, Caching, andthe Complexities ofMultisite(A brief overview.)

Basic Caching withTransients

Transients are ideal for:Temporary data that canexpire at will.

$value = get_transient( big_data );if ( false === $value ) { // do something that takes a fair amount of time $response = wp_remote_get( $url ); $value = wp_remote_retrieve_body( $response ); set_transient( big_data, $value, 60 * 60 * 24 );}echo $value;

$value = get_transient( big_data );if ( false === $value ) { // do something that takes a fair amount of time $response = wp_remote_get( $url ); $value = wp_remote_retrieve_body( $response ); set_transient( big_data, $value ); // this one doesnt expire, but it might anyway}echo $value;

Always persistent:When theres no externalobject cache, WordPressuses the options table.

Object Caching

Object caching is ideal for:Caching an object (often aquery result) to reduceoverhead.

$activity_object = wp_cache_get( $id, activity );if ( false === $activity_object ) { // begrudgingly fetch our object $activity_object = $wpdb->get_row( $wpdb->prepare( "SELECT * FROM $wpdb->activity WHERE ID = %d", $id ) ); wp_cache_set( $id, $activity_object , activity );}// do something with $activity_object

Ideally persistent:Use an object cachingbackend like APC,Memcached, or WinCache.

Object caching is not ideal ifyou need both datapersistence and codeportability.No knowledge of the serversetup? Use transients.

// Cache functions can take an expiration toowp_cache_set( $id, $activity_object , activity, $expires = 0 );

Enter Multisite(Run.)

Site Transients!Well, network-wide transients.Pardon the terminology.

$value = get_site_transient( big_data );if ( false === $value ) { // do something that takes a fair amount of time $response = wp_remote_get( $url ); $value = wp_remote_retrieve_body( $response ); set_site_transient( big_data, $value, 86400 );}echo $value;

Always persistent:When theres no externalobject cache, WordPressuses the sitemeta table.

It works in single-site!When not running multisite,it wraps *_transient().

Global Cache GroupsCache groups (activity) are site-speciﬁc. Tell WordPress what isnt.

// WordPress core (simpliﬁed)wp_cache_add_global_groups( array( users, user_meta, site-transient, site-options, site-lookup, blog-lookup, blog-details, ));// You (not simpliﬁed)wp_cache_add_global_groups( activity );

As you might expect, it worksjust ﬁne in single-site.

And then theresswitch_to_blog()With great power comesgreat responsibility.

Rule 1Dont use it.If you do, cache around it.

// Example is a widget with posts from another site:$posts = wp_cache_get( recent_posts, $blog_id );if ( false === $posts ) { switch_to_blog( $blog_id ); $posts = new WP_Query( . . . )->posts; wp_cache_set( $blog_id, $posts, recent_posts ); restore_current_blog(); // OMG BBQ}// do something with $posts

// And for some extra credit:add_action( init, function() { wp_cache_add_global_groups( recent_posts );} );add_action( save_post, function() { global $blog_id; if ( ! in_array( $blog_id, array( 1, 2 3, 4 ) ) return; wp_cache_delete( $blog_id, recent_posts ); // And for even more extra credit: $posts = new WP_Query( . . . )->posts; wp_cache_add( $blog_id, $posts, recent_posts );} );

Thanks! Questions?@otto42 @nacin

http://www.arastoo.com	155
http://wpspeciali.st	93
http://lanyrd.com	13
http://paper.li	11
https://twitter.com	8
http://localhost	5
http://twitter.com	3
http://0.highlight_server.history.ya.borg.google.com:25414	2
http://a0.twimg.com	1
http://duckduckgo.com	1
http://us-w1.rockmelt.com	1

WordCamp San Francisco 2011: Transients, Caching, and the Complexities of Multisite

by andrewnacin

Accessibility

Upload Details

Usage Rights

11 Embeds 293

Statistics

WordCamp San Francisco 2011: Transients, Caching, and the Complexities of Multisite Presentation Transcript