Changeset 37625

Timestamp:

06/02/2016 06:27:43 PM (8 years ago)

Author:

boonebgorges

Message:

Comments: Improve caching for hierarchical queries.

Hierarchical comment queries work by first fetching the IDs of top-level
comments, and then filling the descendant tree one level at a time based on the
top-level results. When top-level comment IDs are found in the cache,
WP_Comment_Query does not generate the SQL used to fetch these comments. In
this case, the fill_descendants() query does not have enough information
to fill children. As a result, descendant comments were failing to be filled
in cases where the top-level comments were found in the cache.

This was a minor bug previously, because comment caches were not maintained
between pageloads. Since comment caches are now persistent [37613], the problem
becomes evident anywhere that a persistent object cache is in use.

The solution is to cache parent-child relationships, so that when top-level
comments are found in the cache, descendant comments should be found there as
well.

Fixes #36487.

Location:

trunk

Files:

• src/wp-includes/class-wp-comment-query.php (modified) (2 diffs)
• tests/phpunit/tests/comment/query.php (modified) (1 diff)

trunk/src/wp-includes/class-wp-comment-query.php

@@ -743 +743 @@
         }
 
-        if ( $this->query_vars['hierarchical'] && ! $this->query_vars['parent'] ) {
-            $this->query_vars['parent'] = 0;
-        }
-
-        if ( '' !== $this->query_vars['parent'] ) {
-            $this->sql_clauses['where']['parent'] = $wpdb->prepare( 'comment_parent = %d', $this->query_vars['parent'] );
+        $parent = $this->query_vars['parent'];
+        if ( $this->query_vars['hierarchical'] && ! $parent ) {
+            $parent = 0;
+        }
+
+        if ( '' !== $parent ) {
+            $this->sql_clauses['where']['parent'] = $wpdb->prepare( 'comment_parent = %d', $parent );
         }
 
@@ -942 +943 @@
         }
 
+        $key = md5( serialize( wp_array_slice_assoc( $this->query_vars, array_keys( $this->query_var_defaults ) ) ) );
+        $last_changed = wp_cache_get( 'last_changed', 'comment' );
+        if ( ! $last_changed ) {
+            $last_changed = microtime();
+            wp_cache_set( 'last_changed', $last_changed, 'comment' );
+        }
+
         // Fetch an entire level of the descendant tree at a time.
         $level = 0;
         do {
-            $parent_ids = $levels[ $level ];
-            if ( ! $parent_ids ) {
-                break;
-            }
-
-            $where = 'WHERE ' . $_where . ' AND comment_parent IN (' . implode( ',', array_map( 'intval', $parent_ids ) ) . ')';
-            $comment_ids = $wpdb->get_col( "{$this->sql_clauses['select']} {$this->sql_clauses['from']} {$where} {$this->sql_clauses['groupby']} ORDER BY comment_date_gmt ASC, comment_ID ASC" );
+            // Parent-child relationships may be cached. Only query for those that are not.
+            $child_ids = $uncached_parent_ids = array();
+            $_parent_ids = $levels[ $level ];
+            foreach ( $_parent_ids as $parent_id ) {
+                $cache_key = "get_comment_child_ids:$parent_id:$key:$last_changed";
+                $parent_child_ids = wp_cache_get( $cache_key, 'comment' );
+                if ( false !== $parent_child_ids ) {
+                    $child_ids = array_merge( $child_ids, $parent_child_ids );
+                } else {
+                    $uncached_parent_ids[] = $parent_id;
+                }
+            }
+
+            if ( $uncached_parent_ids ) {
+                $where = 'WHERE ' . $_where . ' AND comment_parent IN (' . implode( ',', array_map( 'intval', $uncached_parent_ids ) ) . ')';
+                $level_comments = $wpdb->get_results( "SELECT $wpdb->comments.comment_ID, $wpdb->comments.comment_parent {$this->sql_clauses['from']} {$where} {$this->sql_clauses['groupby']} ORDER BY comment_date_gmt ASC, comment_ID ASC" );
+
+                // Cache parent-child relationships.
+                $parent_map = array_fill_keys( $uncached_parent_ids, array() );
+                foreach ( $level_comments as $level_comment ) {
+                    $parent_map[ $level_comment->comment_parent ][] = $level_comment->comment_ID;
+                    $child_ids[] = $level_comment->comment_ID;
+                }
+
+                foreach ( $parent_map as $parent_id => $children ) {
+                    $cache_key = "get_comment_child_ids:$parent_id:$key:$last_changed";
+                    wp_cache_set( $cache_key, $children, 'comment' );
+                }
+            }
 
             $level++;
-            $levels[ $level ] = $comment_ids;
-        } while ( $comment_ids );
+            $levels[ $level ] = $child_ids;
+        } while ( $child_ids );
 
         // Prime comment caches for non-top-level comments.

trunk/tests/phpunit/tests/comment/query.php

@@ -2431 +2431 @@
         return $clauses;
     }
+
+    /**
+     * @ticket 36487
+     */
+    public function test_cache_should_be_hit_when_querying_descendants() {
+        global $wpdb;
+
+        $p = self::factory()->post->create();
+        $comment_1 = self::factory()->comment->create( array(
+            'comment_post_ID' => $p,
+            'comment_approved' => '1',
+        ) );
+        $comment_2 = self::factory()->comment->create( array(
+            'comment_post_ID' => $p,
+            'comment_approved' => '1',
+            'comment_parent' => $comment_1,
+        ) );
+        $comment_3 = self::factory()->comment->create( array(
+            'comment_post_ID' => $p,
+            'comment_approved' => '1',
+            'comment_parent' => $comment_1,
+        ) );
+        $comment_4 = self::factory()->comment->create( array(
+            'comment_post_ID' => $p,
+            'comment_approved' => '1',
+            'comment_parent' => $comment_2,
+        ) );
+
+        $q1 = new WP_Comment_Query( array(
+            'post_id' => $p,
+            'hierarchical' => true,
+        ) );
+        $q1_ids = wp_list_pluck( $q1->comments, 'comment_ID' );
+
+        $num_queries = $wpdb->num_queries;
+        $q2 = new WP_Comment_Query( array(
+            'post_id' => $p,
+            'hierarchical' => true,
+        ) );
+        $q2_ids = wp_list_pluck( $q2->comments, 'comment_ID' );
+
+        $this->assertEqualSets( $q1_ids, $q2_ids );
+        $this->assertSame( $num_queries, $wpdb->num_queries );
+    }
+
     /**
      * @ticket 27571