Query: Improve cache key generation.

Query caching in `WP_Query` was added in [53941]. When this functionality was added to the `WP_Query` class, a number of edge cases were missed that would result in redundant duplicate queries. It was possible to pass parameters to `WP_Query` that would be different but would result in the same database query being generated. As the cache key is generated from a mixture of query arguments and the SQL query, this resulted in different cache keys for the same database query, resulting in unnecessary duplicate queries. In this change, the logic in the `generate_cache_key` method has been improved to ensure reuse of existing caches. The following edge cases have been considered:

- Passing `post_type` as an empty string.
- Passing `post_type` as the string `any`.
- Passing `post_type` as array vs. string.
- Passing `post_type` as an array in a different order.
- Not passing `orderby`.
- Passing `post_status` as an array vs. string.
- Passing `post_status` as an array in a different order.

This change also fixes an issue where the old SQL query would not match, as the queries had different whitespaces. 

Props spacedmonkey, joemcgill, pbearne, peterwilsoncc, rajinsharwar, mukesh27, thekt12, huzaifaalmesbah, rodionov201.
Fixes #59442.
Built from https://develop.svn.wordpress.org/trunk@58122


git-svn-id: http://core.svn.wordpress.org/trunk@57587 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-wp-query.php

@@ -2264,6 +2264,9 @@ class WP_Query {
 					$post_type = 'any';
 				} elseif ( count( $post_type ) === 1 ) {
 					$post_type = $post_type[0];
+				} else {
+					// Sort post types to ensure same cache key generation.
+					sort( $post_type );
 				}
 
 				$post_status_join = true;
@@ -2542,6 +2545,8 @@ class WP_Query {
 				$post_type_where = " AND {$wpdb->posts}.post_type IN ('" . implode( "', '", array_map( 'esc_sql', $in_search_post_types ) ) . "')";
 			}
 		} elseif ( ! empty( $post_type ) && is_array( $post_type ) ) {
+			// Sort post types to ensure same cache key generation.
+			sort( $post_type );
 			$post_type_where = " AND {$wpdb->posts}.post_type IN ('" . implode( "', '", esc_sql( $post_type ) ) . "')";
 		} elseif ( ! empty( $post_type ) ) {
 			$post_type_where  = $wpdb->prepare( " AND {$wpdb->posts}.post_type = %s", $post_type );
@@ -2647,7 +2652,7 @@ class WP_Query {
 			}
 
 			if ( ! empty( $queried_post_types ) ) {
-
+				sort( $queried_post_types );
 				$status_type_clauses = array();
 
 				foreach ( $queried_post_types as $queried_post_type ) {
@@ -3104,14 +3109,24 @@ class WP_Query {
 			$found_rows = 'SQL_CALC_FOUND_ROWS';
 		}
 
-		// Beginning of the string is on a new line to prevent leading whitespace. See https://core.trac.wordpress.org/ticket/56841.
+		/*
+		 * Beginning of the string is on a new line to prevent leading whitespace.
+		 *
+		 * The additional indentation of subsequent lines is to ensure the SQL
+		 * queries are identical to those generated when splitting queries. This
+		 * improves caching of the query by ensuring the same cache key is
+		 * generated for the same database queries functionally.
+		 *
+		 * See https://core.trac.wordpress.org/ticket/56841.
+		 * See https://github.com/WordPress/wordpress-develop/pull/6393#issuecomment-2088217429
+		 */
 		$old_request =
 			"SELECT $found_rows $distinct $fields
-			 FROM {$wpdb->posts} $join
-			 WHERE 1=1 $where
-			 $groupby
-			 $orderby
-			 $limits";
+					 FROM {$wpdb->posts} $join
+					 WHERE 1=1 $where
+					 $groupby
+					 $orderby
+					 $limits";
 
 		$this->request = $old_request;
 
@@ -4856,6 +4871,32 @@ class WP_Query {
 			$args['suppress_filters']
 		);
 
+		if ( empty( $args['post_type'] ) ) {
+			if ( $this->is_attachment ) {
+				$args['post_type'] = 'attachment';
+			} elseif ( $this->is_page ) {
+				$args['post_type'] = 'page';
+			} else {
+				$args['post_type'] = 'post';
+			}
+		} elseif ( 'any' === $args['post_type'] ) {
+			$args['post_type'] = array_values( get_post_types( array( 'exclude_from_search' => false ) ) );
+		}
+		$args['post_type'] = (array) $args['post_type'];
+		// Sort post types to ensure same cache key generation.
+		sort( $args['post_type'] );
+
+		if ( isset( $args['post_status'] ) ) {
+			$args['post_status'] = (array) $args['post_status'];
+			// Sort post status to ensure same cache key generation.
+			sort( $args['post_status'] );
+		}
+
+		// Add a default orderby value of date to ensure same cache key generation.
+		if ( ! isset( $q['orderby'] ) ) {
+			$args['orderby'] = 'date';
+		}
+
 		$placeholder = $wpdb->placeholder_escape();
 		array_walk_recursive(
 			$args,
@@ -4874,6 +4915,8 @@ class WP_Query {
 			}
 		);
 
+		ksort( $args );
+
 		// Replace wpdb placeholder in the SQL statement used by the cache key.
 		$sql = $wpdb->remove_placeholder_escape( $sql );
 		$key = md5( serialize( $args ) . $sql );

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.6-alpha-58121';
+$wp_version = '6.6-alpha-58122';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.