General: Improve caching in get_calendar function.

Replace the monolithic calendar cache (single array storing all variations)
with individual cache keys per calendar variation, reducing deserialization
overhead on cache reads.

Switch cache invalidation from `save_post` and `delete_post` hooks to
`clean_post_cache`, which avoids unnecessary cache flushes on autosaves,
revision cleanup, and draft saves.

Use `wp_cache_flush_group()` to invalidate all calendar cache entries,
with a generation counter fallback for object cache implementations
that do not support group flushing.

Replace MySQL date arithmetic query with PHP native `gmdate()` to
eliminate an unnecessary database roundtrip for week-to-month
calculation.

Props spacedmonkey, narenin.
Fixes #61343.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: MarcinDudekDev

src/wp-includes/default-filters.php

@@ -565,8 +565,7 @@
 add_action( 'init', 'wp_initialize_site_preview_hooks', 1 );
 
 // Calendar widget cache.
-add_action( 'save_post', 'delete_get_calendar_cache' );
-add_action( 'delete_post', 'delete_get_calendar_cache' );
+add_action( 'clean_post_cache', 'delete_get_calendar_cache' );
 add_action( 'update_option_start_of_week', 'delete_get_calendar_cache' );
 add_action( 'update_option_gmt_offset', 'delete_get_calendar_cache' );
 

src/wp-includes/general-template.php

@@ -2341,12 +2341,18 @@ function get_calendar( $args = array() ) {
 	);
 
 	wp_recursive_ksort( $cache_args );
-	$key   = md5( serialize( $cache_args ) );
-	$cache = wp_cache_get( 'get_calendar', 'calendar' );
 
-	if ( $cache && is_array( $cache ) && isset( $cache[ $key ] ) ) {
+	if ( ! wp_cache_supports( 'flush_group' ) ) {
+		$generation                  = wp_cache_get( 'get_calendar_generation', 'calendar' );
+		$cache_args['_generation_'] = $generation ? (int) $generation : 0;
+	}
+
+	$key   = 'get_calendar_' . md5( serialize( $cache_args ) );
+	$cache = wp_cache_get( $key, 'calendar' );
+
+	if ( false !== $cache ) {
 		/** This filter is documented in wp-includes/general-template.php */
-		$output = apply_filters( 'get_calendar', $cache[ $key ], $args );
+		$output = apply_filters( 'get_calendar', $cache, $args );
 
 		if ( $args['display'] ) {
 			echo $output;
@@ -2356,10 +2362,6 @@ function get_calendar( $args = array() ) {
 		return $output;
 	}
 
-	if ( ! is_array( $cache ) ) {
-		$cache = array();
-	}
-
 	$post_type = $args['post_type'];
 
 	// Quick check. If we have no posts at all, abort!
@@ -2376,8 +2378,7 @@ function get_calendar( $args = array() ) {
 		);
 
 		if ( ! $gotsome ) {
-			$cache[ $key ] = '';
-			wp_cache_set( 'get_calendar', $cache, 'calendar' );
+			wp_cache_set( $key, '', 'calendar' );
 			return;
 		}
 	}
@@ -2390,17 +2391,10 @@ function get_calendar( $args = array() ) {
 		$thismonth = (int) $monthnum;
 		$thisyear  = (int) $year;
 	} elseif ( ! empty( $w ) ) {
-		// We need to get the month from MySQL.
 		$thisyear = (int) substr( $m, 0, 4 );
 		// It seems MySQL's weeks disagree with PHP's.
 		$d         = ( ( $w - 1 ) * 7 ) + 6;
-		$thismonth = (int) $wpdb->get_var(
-			$wpdb->prepare(
-				"SELECT DATE_FORMAT((DATE_ADD('%d0101', INTERVAL %d DAY) ), '%%m')",
-				$thisyear,
-				$d
-			)
-		);
+		$thismonth = (int) gmdate( 'm', strtotime( "{$thisyear}-01-01 + {$d} days" ) );
 	} elseif ( ! empty( $m ) ) {
 		$thisyear = (int) substr( $m, 0, 4 );
 		if ( strlen( $m ) < 6 ) {
@@ -2583,8 +2577,7 @@ function get_calendar( $args = array() ) {
 	$calendar_output .= '
 	</nav>';
 
-	$cache[ $key ] = $calendar_output;
-	wp_cache_set( 'get_calendar', $cache, 'calendar' );
+	wp_cache_set( $key, $calendar_output, 'calendar' );
 
 	/**
 	 * Filters the HTML calendar output.
@@ -2618,7 +2611,13 @@ function get_calendar( $args = array() ) {
  * @since 2.1.0
  */
 function delete_get_calendar_cache() {
-	wp_cache_delete( 'get_calendar', 'calendar' );
+	if ( wp_cache_supports( 'flush_group' ) ) {
+		wp_cache_flush_group( 'calendar' );
+		return;
+	}
+
+	// Fallback for object cache implementations that do not support flushing groups.
+	wp_cache_incr( 'get_calendar_generation', 1, 'calendar' );
 }
 
 /**

tests/phpunit/tests/general/getCalendar.php

@@ -183,7 +183,7 @@ public function test_get_calendar_caching_accounts_for_equivalent_args() {
 	public function test_get_calendar_backwards_compatibility() {
 		$first_calendar_html = get_echo( 'get_calendar', array( false ) );
 
-		wp_cache_delete( 'get_calendar', 'calendar' );
+		delete_get_calendar_cache();
 
 		$second_calendar_html = get_calendar( false, false );
 
@@ -192,4 +192,75 @@ public function test_get_calendar_backwards_compatibility() {
 		$this->assertStringContainsString( '<table id="wp-calendar"', $first_calendar_html, 'Calendar is expected to contain the element table#wp-calendar' );
 		$this->assertSame( $first_calendar_html, $second_calendar_html, 'Both calendars should be identical' );
 	}
+
+	/**
+	 * Test that clean_post_cache invalidates the calendar cache.
+	 *
+	 * @ticket 61343
+	 */
+	public function test_clean_post_cache_invalidates_calendar_cache() {
+		// Populate the cache.
+		get_echo( 'get_calendar' );
+
+		$num_queries_start = get_num_queries();
+		get_echo( 'get_calendar' );
+		$queries_cached = get_num_queries() - $num_queries_start;
+
+		$this->assertSame( 0, $queries_cached, 'Second call should be cached with zero queries.' );
+
+		// Simulate clean_post_cache firing.
+		delete_get_calendar_cache();
+
+		$num_queries_start = get_num_queries();
+		get_echo( 'get_calendar' );
+		$queries_after_flush = get_num_queries() - $num_queries_start;
+
+		$this->assertGreaterThan( 0, $queries_after_flush, 'After cache flush, queries should run again.' );
+	}
+
+	/**
+	 * Test that the calendar uses individual cache keys per variation.
+	 *
+	 * @ticket 61343
+	 */
+	public function test_calendar_uses_individual_cache_keys() {
+		// Generate calendar for 'post' type.
+		get_echo( 'get_calendar' );
+
+		// Generate calendar for 'page' type.
+		get_echo( 'get_calendar', array( array( 'post_type' => 'page' ) ) );
+
+		$num_queries_start = get_num_queries();
+
+		// Both should be cached independently.
+		get_echo( 'get_calendar' );
+		get_echo( 'get_calendar', array( array( 'post_type' => 'page' ) ) );
+
+		$this->assertSame( 0, get_num_queries() - $num_queries_start, 'Both variations should be served from cache with zero queries.' );
+	}
+
+	/**
+	 * Test that flush_group clears all calendar variations at once.
+	 *
+	 * @ticket 61343
+	 */
+	public function test_flush_group_clears_all_variations() {
+		// Populate caches for two different post types.
+		get_echo( 'get_calendar' );
+		get_echo( 'get_calendar', array( array( 'post_type' => 'page' ) ) );
+
+		// Flush all calendar cache.
+		delete_get_calendar_cache();
+
+		$num_queries_start = get_num_queries();
+		get_echo( 'get_calendar' );
+		$queries_post = get_num_queries() - $num_queries_start;
+
+		$num_queries_start = get_num_queries();
+		get_echo( 'get_calendar', array( array( 'post_type' => 'page' ) ) );
+		$queries_page = get_num_queries() - $num_queries_start;
+
+		$this->assertGreaterThan( 0, $queries_post, 'Post calendar should require queries after flush.' );
+		$this->assertGreaterThan( 0, $queries_page, 'Page calendar should require queries after flush.' );
+	}
 }