Changeset 28972

Timestamp:

07/03/2014 04:44:15 PM (10 years ago)

Author:

helen

Message:

Improve oEmbed caching. Introduces the concept of a TTL for oEmbed caches and a filter for oembed_ttl.

We will no longer replace previously valid oEmbed responses with an {{unknown}} cache value. When this happens due to reaching a rate limit or a service going down, it is data loss, and is not acceptable. This means that oEmbed caches for a post are no longer deleted indiscriminately every time that post is saved.

oEmbed continues to be cached in post meta, with the addition of a separate meta key containing the timestamp of the last retrieval, which is used to avoid re-requesting a recently cached oEmbed response. By default, we consider a valued cached in the past day to be fresh. This can greatly reduce the number of outbound requests, especially in cases where a post containing multiple embeds is saved frequently.

The TTL used to determine whether or not to request a response can be filtered using oembed_ttl, thus allowing for the possibility of respecting the optional oEmbed response parameter cache_age or altering the period of time a cached value is considered to be fresh.

Now that oEmbeds are previewed in the visual editor as well as the media modal, oEmbed caches are often populated before a post is saved or published. By pre-populating and avoiding having to re-request that response, we also greatly reduce the chances of a stampede happening when a published post is visible before oEmbed caching is complete.

As it previously stood, a stampede was extremely likely to happen, as the AJAX caching was only triggered when $_GET['message'] was 1. The published message is 6. We now trigger the caching every time $_GET['message'] is present on the edit screen, as we are able to avoid triggering so many HTTP requests overall.

props markjaquith. fixes #14759. see #17210.

Location:

trunk/src

Files:

• wp-admin/includes/ajax-actions.php (modified) (1 diff)
• wp-includes/class-wp-embed.php (modified) (6 diffs)

trunk/src/wp-admin/includes/ajax-actions.php

@@ -226 +226 @@
  */
 function wp_ajax_oembed_cache() {
-    global $wp_embed;
-
-    $return = ( $wp_embed->cache_oembed( $_GET['post'] ) ) ? '1' : '0';
-    wp_die( $return );
+    $GLOBALS['wp_embed']->cache_oembed( $_GET['post'] );
+    wp_die( 0 );
 }
 

trunk/src/wp-includes/class-wp-embed.php

@@ -32 +32 @@
         add_filter( 'the_content', array( $this, 'autoembed' ), 8 );
 
-        // When a post is saved, invalidate the oEmbed cache
-        add_action( 'pre_post_update', array( $this, 'delete_oembed_caches' ) );
-
         // After a post is saved, cache oEmbed items via AJAX
         add_action( 'edit_form_advanced', array( $this, 'maybe_run_ajax_cache' ) );
@@ -79 +76 @@
         $post = get_post();
 
-        if ( ! $post || empty($_GET['message']) || 1 != $_GET['message'] )
+        if ( ! $post || empty( $_GET['message'] ) )
             return;
 
@@ -193 +190 @@
 
             // Check for a cached result (stored in the post meta)
-            $cachekey = '_oembed_' . md5( $url . serialize( $attr ) );
-            if ( $this->usecache ) {
-                $cache = get_post_meta( $post_ID, $cachekey, true );
-
-                // Failures are cached
+            $key_suffix = md5( $url . serialize( $attr ) );
+            $cachekey = '_oembed_' . $key_suffix;
+            $cachekey_time = '_oembed_time_' . $key_suffix;
+
+            /**
+             * Filter the oEmbed TTL (time to live).
+             *
+             * @since 4.0.0
+             *
+             * @param string $url     The attempted embed URL.
+             * @param array  $attr    An array of shortcode attributes.
+             * @param int    $post_ID Post ID.
+             */
+            $ttl = apply_filters( 'oembed_ttl', DAY_IN_SECONDS, $url, $attr, $post_ID );
+
+            $cache = get_post_meta( $post_ID, $cachekey, true );
+            $cache_time = get_post_meta( $post_ID, $cachekey_time, true );
+
+            if ( ! $cache_time ) {
+                $cache_time = 0;
+            }
+
+            $cached_recently = ( time() - $cache_time ) < $ttl;
+
+            if ( $this->usecache || $cached_recently ) {
+                // Failures are cached. Serve one if we're using the cache.
                 if ( '{{unknown}}' === $cache )
                     return $this->maybe_make_link( $url );
 
-                if ( ! empty( $cache ) )
+                if ( ! empty( $cache ) ) {
                     /**
                      * Filter the cached oEmbed HTML.
@@ -215 +233 @@
                      */
                     return apply_filters( 'embed_oembed_html', $cache, $url, $attr, $post_ID );
+                }
             }
 
@@ -231 +250 @@
             $html = wp_oembed_get( $url, $attr );
 
-            // Cache the result
-            $cache = ( $html ) ? $html : '{{unknown}}';
-            update_post_meta( $post_ID, $cachekey, $cache );
+            // Maybe cache the result
+            if ( $html ) {
+                update_post_meta( $post_ID, $cachekey, $html );
+                update_post_meta( $post_ID, $cachekey_time, time() );
+            } elseif ( ! $cache ) {
+                update_post_meta( $post_ID, $cachekey, '{{unknown}}' );
+            }
 
             // If there was a result, return it
@@ -247 +270 @@
 
     /**
-     * Delete all oEmbed caches.
+     * Delete all oEmbed caches. Unused by core as of 4.0.0.
      *
      * @param int $post_ID Post ID to delete the caches for.