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<title>[28972] trunk/src: Improve oEmbed caching.</title>
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<dl class="meta">
<dt>Revision</dt> <dd><a href="http://core.trac.wordpress.org/changeset/28972">28972</a></dd>
<dt>Author</dt> <dd>helen</dd>
<dt>Date</dt> <dd>2014-07-03 16:44:15 +0000 (Thu, 03 Jul 2014)</dd>
</dl>
<h3>Log Message</h3>
<pre>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 <a href="http://core.trac.wordpress.org/ticket/14759">#14759</a>. see <a href="http://core.trac.wordpress.org/ticket/17210">#17210</a>.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunksrcwpadminincludesajaxactionsphp">trunk/src/wp-admin/includes/ajax-actions.php</a></li>
<li><a href="#trunksrcwpincludesclasswpembedphp">trunk/src/wp-includes/class-wp-embed.php</a></li>
</ul>
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<h3>Diff</h3>
<a id="trunksrcwpadminincludesajaxactionsphp"></a>
<div class="modfile"><h4>Modified: trunk/src/wp-admin/includes/ajax-actions.php (28971 => 28972)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/src/wp-admin/includes/ajax-actions.php 2014-07-03 16:21:18 UTC (rev 28971)
+++ trunk/src/wp-admin/includes/ajax-actions.php 2014-07-03 16:44:15 UTC (rev 28972)
</span><span class="lines">@@ -225,10 +225,8 @@
</span><span class="cx"> * @since 3.1.0
</span><span class="cx"> */
</span><span class="cx"> function wp_ajax_oembed_cache() {
</span><del>- global $wp_embed;
-
- $return = ( $wp_embed->cache_oembed( $_GET['post'] ) ) ? '1' : '0';
- wp_die( $return );
</del><ins>+ $GLOBALS['wp_embed']->cache_oembed( $_GET['post'] );
+ wp_die( 0 );
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> /**
</span></span></pre></div>
<a id="trunksrcwpincludesclasswpembedphp"></a>
<div class="modfile"><h4>Modified: trunk/src/wp-includes/class-wp-embed.php (28971 => 28972)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/src/wp-includes/class-wp-embed.php 2014-07-03 16:21:18 UTC (rev 28971)
+++ trunk/src/wp-includes/class-wp-embed.php 2014-07-03 16:44:15 UTC (rev 28972)
</span><span class="lines">@@ -31,9 +31,6 @@
</span><span class="cx"> // Attempts to embed all URLs in a post
</span><span class="cx"> add_filter( 'the_content', array( $this, 'autoembed' ), 8 );
</span><span class="cx">
</span><del>- // When a post is saved, invalidate the oEmbed cache
- add_action( 'pre_post_update', array( $this, 'delete_oembed_caches' ) );
-
</del><span class="cx"> // After a post is saved, cache oEmbed items via AJAX
</span><span class="cx"> add_action( 'edit_form_advanced', array( $this, 'maybe_run_ajax_cache' ) );
</span><span class="cx"> }
</span><span class="lines">@@ -78,7 +75,7 @@
</span><span class="cx"> public function maybe_run_ajax_cache() {
</span><span class="cx"> $post = get_post();
</span><span class="cx">
</span><del>- if ( ! $post || empty($_GET['message']) || 1 != $_GET['message'] )
</del><ins>+ if ( ! $post || empty( $_GET['message'] ) )
</ins><span class="cx"> return;
</span><span class="cx">
</span><span class="cx"> ?>
</span><span class="lines">@@ -192,15 +189,36 @@
</span><span class="cx"> if ( $post_ID ) {
</span><span class="cx">
</span><span class="cx"> // Check for a cached result (stored in the post meta)
</span><del>- $cachekey = '_oembed_' . md5( $url . serialize( $attr ) );
- if ( $this->usecache ) {
- $cache = get_post_meta( $post_ID, $cachekey, true );
</del><ins>+ $key_suffix = md5( $url . serialize( $attr ) );
+ $cachekey = '_oembed_' . $key_suffix;
+ $cachekey_time = '_oembed_time_' . $key_suffix;
</ins><span class="cx">
</span><del>- // Failures are cached
</del><ins>+ /**
+ * 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.
</ins><span class="cx"> if ( '{{unknown}}' === $cache )
</span><span class="cx"> return $this->maybe_make_link( $url );
</span><span class="cx">
</span><del>- if ( ! empty( $cache ) )
</del><ins>+ if ( ! empty( $cache ) ) {
</ins><span class="cx"> /**
</span><span class="cx"> * Filter the cached oEmbed HTML.
</span><span class="cx"> *
</span><span class="lines">@@ -214,6 +232,7 @@
</span><span class="cx"> * @param int $post_ID Post ID.
</span><span class="cx"> */
</span><span class="cx"> return apply_filters( 'embed_oembed_html', $cache, $url, $attr, $post_ID );
</span><ins>+ }
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> /**
</span><span class="lines">@@ -230,9 +249,13 @@
</span><span class="cx"> // Use oEmbed to get the HTML
</span><span class="cx"> $html = wp_oembed_get( $url, $attr );
</span><span class="cx">
</span><del>- // Cache the result
- $cache = ( $html ) ? $html : '{{unknown}}';
- update_post_meta( $post_ID, $cachekey, $cache );
</del><ins>+ // 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}}' );
+ }
</ins><span class="cx">
</span><span class="cx"> // If there was a result, return it
</span><span class="cx"> if ( $html ) {
</span><span class="lines">@@ -246,7 +269,7 @@
</span><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> /**
</span><del>- * Delete all oEmbed caches.
</del><ins>+ * Delete all oEmbed caches. Unused by core as of 4.0.0.
</ins><span class="cx"> *
</span><span class="cx"> * @param int $post_ID Post ID to delete the caches for.
</span><span class="cx"> */
</span></span></pre>
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