Intro to advanced caching in WordPress

Presented at WordCamp Jerusalem 2013 (Feb. 20, 2013)

Transcript

1. Advanced Caching An Introduction to methods in WordPress
2. Maor Chasen WP Developer @ illuminea Core contributor for 3.5 Have plugins on WordPress.org Open Source Fanatic Design Enthusiast Flying kites
4. It's not scary. It's fun.
5. 1. It's easy 2. Your site = faster 3. Can save you $$ 4. It will knock your socks off 5. You'll sleep better at night. Why caching is good for you? A question you shouldn't ask your mom
6. What we will talk about • What is fragment / object caching • Why caching is important • How to cache • What to cache • When to cache
7. What we won't talk about • Server setups • Caching plugins
9. Transients API first things first
10. Transients are • temporary bits of data (usually raw data) • like options, but w/ expiration time • always persistent out of the box • stored in wp_options by default • stored in memory if a caching backend (APC, Memcache, XCache, etc.) is available • available since 2.8
11. • fetching data from a remote source • performing an expensive* query or request ◦ meta_query ◦ tax_query • data persistence is absolutely required** Use Transients when * operations that require high CPU usage or high latency (Identify slow queries with Debug Bar) ** ex. - when polling data from external sources
12. Transients functions at your disposal read core? wp-includes/option.php
13. get_transient( $transient ); Get it. unique string (key) representing a piece of data
14. set_transient( $transient, $value, $expiration = 0 ); Set it. the data you wish to store for how long?
15. delete_transient( $transient ); Scrap it. unique string (key) representing a piece of data
16. get_site_transient(); set_site_transient(); delete_site_transient(); Multisite? You're in luck! All Transients functions have their network-wide counterparts.
17. Use case: Using Transients to store fragmented data
18. wp_nav_menu( array( 'theme_location' => 'primary', ) ); <ul id="menu-primary" class="menu"> <li id="menu-item-10" class="menu-item"> <a href="...">...</a> </li> ... </ul>
19. Without using wp_nav_menu() After using wp_nav_menu() That is ~5 extra queries (for each menu)
20. Instead, we can cache the menu in a transient and save on DB queries
21. // Get an existing copy of our transient data $menu_html = get_transient( 'wcj_2013_menu' ); if ( false === $menu_html ) { // data is not available, let's generate it $menu_html = wp_nav_menu( array( 'theme_location' => 'primary', 'echo' => false, ) ); set_transient( 'wcj_2013_menu', $menu_html, DAY_IN_SECONDS ); } // do something with $menu_html echo $menu_html; 60 * 60 * 24 returns the menu instead of printing
22. // Get an existing copy of our transient data $menu_html = get_transient( 'wcj_2013_menu' ); if ( false === $menu_html ) { // data is not available, let's generate it $menu_html = wp_nav_menu( array( 'theme_location' => 'primary', 'echo' => false, ) ); set_transient( 'wcj_2013_menu', $menu_html ); } // do something with $menu_html echo $menu_html; doesn't expire, but it might anyway
23. function wcj_2013_invldt_menu( $menu_id, $menu_data ) { delete_transient( 'wcj_2013_menu' ); } add_action( 'wp_update_nav_menu', 'wcj_2013_invldt_menu', 10, 2 ); Now, let's invalidate this action runs whenever a menu is being saved
24. Use Transients when fetching data from a remote source http://... https://...
25. Twitter API Facebook API Google+ API Pick your poison last.fm API
26. Example (Twitter API): Retrieve follower count and cache the results
27. function wcj_2013_get_twitter_followers_for( $handle ) { $key = "wcj_2013_followers_$handle"; if ( false === ( $followers_count = get_transient( $key ) ) ) { // transient expired, regenerate! $followers_count = wp_remote_retrieve_body( wp_remote_get( "http://api.twitter.com/1/users/show.json? screen_name=$handle" ) ); // request failed? if ( empty( $followers_count ) ) return false; // extract the number of followers $json = (object) json_decode( $followers_count ); $followers_count = absint( $json->followers_count ); // request was complete, store data in a transient for 6 hours set_transient( $key, $followers_count, 6 * HOUR_IN_SECONDS ); } return $followers_count; }
28. function wcj_2013_get_twitter_followers_for( $handle ) { $key = "wcj_2013_followers_$handle"; if ( false === ( $followers_count = get_transient( $key ) ) ) { // transient expired, regenerate! $followers_count = wp_remote_retrieve_body( wp_remote_get( "http://api.twitter.com/1/users/show.json? screen_name=$handle" ) ); // request failed? if ( empty( $followers_count ) ) return false; // extract the number of followers $json = (object) json_decode( $followers_count ); $followers_count = absint( $json->followers_count ); // request was complete, store data in a transient for 6 hours set_transient( $key, $followers_count, 6 * HOUR_IN_SECONDS ); } return $followers_count; }
29. function wcj_2013_get_twitter_followers_for( $handle ) { $key = "wcj_2013_followers_$handle"; if ( false === ( $followers_count = get_transient( $key ) ) ) { // transient expired, regenerate! $followers_count = wp_remote_retrieve_body( wp_remote_get( "http://api.twitter.com/1/users/show.json? screen_name=$handle" ) ); // request failed? if ( empty( $followers_count ) ) return false; // extract the number of followers $json = (object) json_decode( $followers_count ); $followers_count = absint( $json->followers_count ); // request was complete, store data in a transient for 6 hours set_transient( $key, $followers_count, 6 * HOUR_IN_SECONDS ); } return $followers_count; }
30. function wcj_2013_get_twitter_followers_for( $handle ) { $key = "wcj_2013_followers_$handle"; if ( false === ( $followers_count = get_transient( $key ) ) ) { // transient expired, regenerate! $followers_count = wp_remote_retrieve_body( wp_remote_get( "http://api.twitter.com/1/users/show.json? screen_name=$handle" ) ); // request failed? if ( empty( $followers_count ) ) return false; // extract the number of followers $json = (object) json_decode( $followers_count ); $followers_count = absint( $json->followers_count ); // request was complete, store data in a transient for 6 hours set_transient( $key, $followers_count, 6 * HOUR_IN_SECONDS ); } return $followers_count; } printf( 'I have %d followers!', wcj_2013_get_twitter_followers_for( 'maorh' ) );
31. Let's spice it up Got some metrics!
32. Without Transients 0.36014295 seconds WITH Transients 0.00010109 seconds
33. That is 3,562 X FASTER
35. Object Cache API last but not least
36. Object Cache is • non-persistent out of the box • stored in PHP memory by default • ideally* persistent when a caching backend is available • similar to Transients • available since 2.0 * Success depends on server environment
37. Is post_id = 13 cached? Do something with that post Store results in Object Cache DB SELECT * FROM wp_posts WHERE ID = 13 Yes No Common use of the Object Cache API
38. Object Cache functions at your disposal read core? wp-includes/cache.php
39. • wp_cache_add( $k, $d, $g, $ex ) • wp_cache_get( $k ) • wp_cache_set( $k, $d, $g, $ex ) • wp_cache_delete( $k, $g ) • wp_cache_incr( $k, $offset, $g ) Object Cache functions at your disposal $key, $data, $group, $expiration
40. $song_obj = wp_cache_get( $id, 'songs' ); if ( false === $song_obj ) { $song_obj = $wpdb->get_row( $wpdb->prepare( "SELECT * FROM $wpdb->songs WHERE ID = %d", $id ) ); wp_cache_set( $id, $song_obj, 'songs' ); } // do something with $song_obj Example
41. Best Practices for the best of us • prefer refreshing the cache ONLY when data is added/changed • Avoid, if possible, caching on front end page requests (instead, generate the data on an admin event*) • Design to fail gracefully (never assume that data is in the cache) * useful events: publish_post, transition_post_status, created_ {$taxonomy}, edited_{$taxonomy}
42. Out of the box Memory Cache Backend Transients API persistent - database Persistent Object Cache API non-persistent - memory Ideally Persistent http://wordpress.stackexchange.com/a/45137 Side-by-side comparison
43. Questions? Thanks! @maorh keep in touch