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<title>[5124] sites/trunk/wordpress.org/public_html/wp-content/plugins/plugin-directory/libs/site-search/jetpack-search.php: Plugin directory search: improve caching and error handling when calling the remote Jetpack search API.</title>
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<dt style="float: left; width: 6em; font-weight: bold">Revision</dt> <dd><a style="font-weight: bold" href="http://meta.trac.wordpress.org/changeset/5124">5124</a><script type="application/ld+json">{"@context":"http://schema.org","@type":"EmailMessage","description":"Review this Commit","action":{"@type":"ViewAction","url":"http://meta.trac.wordpress.org/changeset/5124","name":"Review Commit"}}</script></dd>
<dt style="float: left; width: 6em; font-weight: bold">Author</dt> <dd>tellyworth</dd>
<dt style="float: left; width: 6em; font-weight: bold">Date</dt> <dd>2017-03-08 08:37:51 +0000 (Wed, 08 Mar 2017)</dd>
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<pre style='padding-left: 1em; margin: 2em 0; border-left: 2px solid #ccc; line-height: 1.25; font-size: 105%; font-family: sans-serif'>Plugin directory search: improve caching and error handling when calling the remote Jetpack search API.
* Prevent stampedes when a cache key expires, by allowing only one remote call per term.
* Back off when errors occur.
* Use trigger_error() so that errors are logged.
Note that error backoff is per-term; this needs to be complemented with a global backoff also.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#sitestrunkwordpressorgpublic_htmlwpcontentpluginsplugindirectorylibssitesearchjetpacksearchphp">sites/trunk/wordpress.org/public_html/wp-content/plugins/plugin-directory/libs/site-search/jetpack-search.php</a></li>
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<h3>Diff</h3>
<a id="sitestrunkwordpressorgpublic_htmlwpcontentpluginsplugindirectorylibssitesearchjetpacksearchphp"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: sites/trunk/wordpress.org/public_html/wp-content/plugins/plugin-directory/libs/site-search/jetpack-search.php</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- sites/trunk/wordpress.org/public_html/wp-content/plugins/plugin-directory/libs/site-search/jetpack-search.php 2017-03-08 03:20:45 UTC (rev 5123)
+++ sites/trunk/wordpress.org/public_html/wp-content/plugins/plugin-directory/libs/site-search/jetpack-search.php 2017-03-08 08:37:51 UTC (rev 5124)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -177,28 +177,69 @@
</span><span class="cx" style="display: block; padding: 0 10px"> $service_url = 'http://public-api.wordpress.com/rest/v1/sites/' . $this->jetpack_blog_id . '/search';
</span><span class="cx" style="display: block; padding: 0 10px"> $json_es_args = json_encode( $es_args );
</span><span class="cx" style="display: block; padding: 0 10px"> $cache_key = md5( $json_es_args );
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ $lock_key = 'lock-'.$cache_key;
</ins><span class="cx" style="display: block; padding: 0 10px">
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- $cached_response = wp_cache_get( $cache_key, self::CACHE_GROUP );
- if ( $cached_response !== false )
- return $cached_response;
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ $response = wp_cache_get( $cache_key, self::CACHE_GROUP );
</ins><span class="cx" style="display: block; padding: 0 10px">
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- $request = wp_remote_post( $service_url, array(
- 'headers' => array(
- 'Content-Type' => 'application/json',
- ),
- 'timeout' => 10,
- 'user-agent' => 'jetpack_search',
- 'body' => $json_es_args,
- ) );
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ // Use a temporary lock to prevent cache stampedes. This ensures only one process (per search term per memcache instance) will run the remote post.
+ // Other processes will use the stale cached value if it's present, even for a while after the expiration time if a fresh value is still being fetched.
+ if ( wp_cache_add( $lock_key, 1, self::CACHE_GROUP, 15 ) ) {
+ $request = wp_remote_post( $service_url, array(
+ 'headers' => array(
+ 'Content-Type' => 'application/json',
+ ),
+ 'timeout' => 10,
+ 'user-agent' => 'jetpack_search',
+ 'body' => $json_es_args,
+ ) );
</ins><span class="cx" style="display: block; padding: 0 10px">
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- if ( is_wp_error( $request ) )
- return $request;
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ // If there's a network or HTTP error, we'll intentionally leave the temporary lock to expire in a few seconds.
+ // Other requests during that window will use the stale cached value. We'll try another remote request once this lock expires.
+ if ( is_wp_error( $request ) || 200 != wp_remote_retrieve_response_code( $request ) ) {
</ins><span class="cx" style="display: block; padding: 0 10px">
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- $response = json_decode( wp_remote_retrieve_body( $request ), true );
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ // Lock further requests for the same search for 3-7 seconds. We probably don't need anything more complex like exponential backoff here because this is per search.
+ wp_cache_set( $lock_key, 1, self::CACHE_GROUP, mt_rand( 3, 7 ) );
</ins><span class="cx" style="display: block; padding: 0 10px">
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- if ( !isset( $response['error'] ) )
- wp_cache_set( $cache_key, $response, self::CACHE_GROUP, self::CACHE_EXPIRY );
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ if ( is_wp_error( $request ) )
+ trigger_error( 'Plugin directory search: http error '.$request->get_error_message(), E_USER_WARNING );
+ else
+ trigger_error( 'Plugin directory search: http status '.wp_remote_retrieve_response_code( $request ), E_USER_WARNING );
</ins><span class="cx" style="display: block; padding: 0 10px">
</span><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ // If we have a stale cached response, return that. Otherwise, return the error object.
+ if ( $response )
+ return $response; // Stale cached response.
+ return $request; // Fresh error object.
+ }
+
+ $fresh_response = json_decode( wp_remote_retrieve_body( $request ), true );
+
+ if ( !$fresh_response || isset( $fresh_response['error'] ) ) {
+ // As above, lock further requests for the same search for a few seconds
+ wp_cache_set( $lock_key, 1, self::CACHE_GROUP, mt_rand( 3, 7 ) );
+
+ if ( isset( $fresh_response['error'] ) )
+ trigger_error( 'Plugin directory search: remote error '.$fresh_response['error'], E_USER_WARNING );
+ else
+ trigger_error( 'Plugin directory search: invalid json response', E_USER_WARNING );
+
+ // Return a stale response if we have one
+ if ( $response )
+ return $response;
+ return $fresh_response; // Fresh error object as a last resort
+
+ } else {
+ // The cached value has a TTL twice as long as the exipration time.
+ // The lock TTL serves as our expiration timer.
+ wp_cache_set( $cache_key, $fresh_response, self::CACHE_GROUP, self::CACHE_EXPIRY * 2 );
+ wp_cache_set( $lock_key, 1, self::CACHE_GROUP, self::CACHE_EXPIRY );
+ $response = $fresh_response;
+ }
+ } else {
+ // Stampede protection has kicked in, AND we have no stale cached value to display. That's bad - possibly indicates cache exhaustion
+ if ( false === $response )
+ trigger_error( 'Plugin directory search: no cached results available during stampede.', E_USER_WARNING );
+ }
+
</ins><span class="cx" style="display: block; padding: 0 10px"> return $response;
</span><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px">
</span></span></pre>
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