From 4127a17a0ae18378ce1c2c3e0511fae24c5b034c Mon Sep 17 00:00:00 2001
From: Peter Wilson <wilson@peterwilson.cc>
Date: Tue, 5 Apr 2022 01:55:03 +0000
Subject: [PATCH] Query: Cache comments feeds in `WP_Query`.

Cache queries to the comments table in `WP_Query` for various comments feeds. Only comment IDs are stored for each feeds cache to avoid doubling up caching with each individual comment's cache.

Props spacedmonkey, boonebgorges, pbearne.
Fixes #36904.


Built from https://develop.svn.wordpress.org/trunk@53065


git-svn-id: http://core.svn.wordpress.org/trunk@52654 1a063a9b-81f0-0310-95a4-ce76da25c4cd
---
 wp-includes/class-wp-query.php | 33 ++++++++++++++++++++++++++++-----
 wp-includes/version.php        |  2 +-
 2 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/wp-includes/class-wp-query.php b/wp-includes/class-wp-query.php
index 35b29a902d..fbba6a5f31 100644
--- a/wp-includes/class-wp-query.php
+++ b/wp-includes/class-wp-query.php
@@ -2720,10 +2720,22 @@ class WP_Query {
 			$corderby = ( ! empty( $corderby ) ) ? 'ORDER BY ' . $corderby : '';
 			$climits  = ( ! empty( $climits ) ) ? $climits : '';
 
-			$comments = (array) $wpdb->get_results( "SELECT $distinct {$wpdb->comments}.* FROM {$wpdb->comments} $cjoin $cwhere $cgroupby $corderby $climits" );
+			$comments_request = "SELECT $distinct {$wpdb->comments}.comment_ID FROM {$wpdb->comments} $cjoin $cwhere $cgroupby $corderby $climits";
+
+			$key          = md5( $comments_request );
+			$last_changed = wp_cache_get_last_changed( 'comment' ) . ':' . wp_cache_get_last_changed( 'posts' );
+
+			$cache_key   = "comment_feed:$key:$last_changed";
+			$comment_ids = wp_cache_get( $cache_key, 'comment' );
+			if ( false === $comment_ids ) {
+				$comment_ids = $wpdb->get_col( $comments_request );
+				wp_cache_add( $cache_key, $comment_ids, 'comment' );
+			}
+			_prime_comment_caches( $comment_ids, false );
+
 			// Convert to WP_Comment.
 			/** @var WP_Comment[] */
-			$this->comments      = array_map( 'get_comment', $comments );
+			$this->comments      = array_map( 'get_comment', $comment_ids );
 			$this->comment_count = count( $this->comments );
 
 			$post_ids = array();
@@ -3164,11 +3176,22 @@ class WP_Query {
 			/** This filter is documented in wp-includes/query.php */
 			$climits = apply_filters_ref_array( 'comment_feed_limits', array( 'LIMIT ' . get_option( 'posts_per_rss' ), &$this ) );
 
-			$comments_request = "SELECT {$wpdb->comments}.* FROM {$wpdb->comments} $cjoin $cwhere $cgroupby $corderby $climits";
-			$comments         = $wpdb->get_results( $comments_request );
+			$comments_request = "SELECT {$wpdb->comments}.comment_ID FROM {$wpdb->comments} $cjoin $cwhere $cgroupby $corderby $climits";
+
+			$key          = md5( $comments_request );
+			$last_changed = wp_cache_get_last_changed( 'comment' );
+
+			$cache_key   = "comment_feed:$key:$last_changed";
+			$comment_ids = wp_cache_get( $cache_key, 'comment' );
+			if ( false === $comment_ids ) {
+				$comment_ids = $wpdb->get_col( $comments_request );
+				wp_cache_add( $cache_key, $comment_ids, 'comment' );
+			}
+			_prime_comment_caches( $comment_ids, false );
+
 			// Convert to WP_Comment.
 			/** @var WP_Comment[] */
-			$this->comments      = array_map( 'get_comment', $comments );
+			$this->comments      = array_map( 'get_comment', $comment_ids );
 			$this->comment_count = count( $this->comments );
 		}
 
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 4857db98d0..21e719ae14 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.0-alpha-53064';
+$wp_version = '6.0-alpha-53065';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.