Introduce flush timeouts

CHANGELOG.md

@@ -9,6 +9,7 @@
 - Renamed `.redis-write-test.tmp` test file to `object-cache.tmp`
 - Call `redis_object_cache_error` action before `wp_die()`
 - Allow `WP_REDIS_PLUGIN_PATH` to be defined elsewhere
+- Added experimental flush timeout (defaults to `5` seconds)
 
 ## 2.4.4
 

FAQ.md

@@ -138,6 +138,14 @@ This can happen when Redis Server runs out of memory and no `maxmemory-policy` w
 Alternatively, you can set the `WP_REDIS_MAXTTL` constant to something relatively low (like `3600` seconds) and flush the cache.
 </details>
 
+<details>
+<summary><code>Flushing the cache causes timeout</code></summary>
+
+This can happen when the dataset in Redis Server is quite large. Consider increasing `WP_REDIS_READ_TIMEOUT` and `WP_REDIS_FLUSH_TIMEOUT` to 5-10 seconds.
+
+Alternatively, starting with Redis 6.2, setting the `lazyfree-lazy-user-flush` in the `redis.conf` configuration directive to `yes` changes the default flush mode to be asynchronous.
+</details>
+
 <details>
 <summary>Unable to flush the cache</summary>
 

README.md

@@ -36,12 +36,12 @@ The Redis Object Cache plugin comes with vast set of configuration options. If y
 | `WP_REDIS_PATH`                      |             | The path to the unix socket of the Redis server |
 | `WP_REDIS_SCHEME`                    | `tcp`       | The scheme used to connect: `tcp` or `unix` |
 | `WP_REDIS_DATABASE`                  | `0`         | The database used by the cache: `0-15` |
-| `WP_REDIS_PREFIX`                    |             | The prefix used for all cache keys to avoid data collisions, replaces `WP_CACHE_KEY_SALT`. Should be human readable, not a "salt". |
-| `WP_REDIS_PASSWORD`                  |             | The password of the Redis server. Supports Redis ACLs arrays: `['user', 'password']` |
+| `WP_REDIS_PREFIX`                    |             | The prefix used for all cache keys to avoid data collisions (replaces `WP_CACHE_KEY_SALT`), should be human readable and not a "salt" |
+| `WP_REDIS_PASSWORD`                  |             | The password of the Redis server, supports Redis ACLs arrays: `['user', 'password']` |
 | `WP_REDIS_MAXTTL`                    | `0`         | The maximum time-to-live of cache keys |
-| `WP_REDIS_CLIENT`                    |             | The client used to communicate with Redis. Defaults to `phpredis` when installed, otherwise `predis`. Supports `phpredis`, `predis`, `relay` |
+| `WP_REDIS_CLIENT`                    |             | The client used to communicate with Redis (defaults to `phpredis` when installed, otherwise `predis`), supports `phpredis`, `predis`, `relay` |
 | `WP_REDIS_TIMEOUT`                   | `1`         | The connection timeout in seconds |
-| `WP_REDIS_READ_TIMEOUT`              | `1`         | The timeout in seconds when reading/writing  |
+| `WP_REDIS_READ_TIMEOUT`              | `1`         | The timeout in seconds when reading/writing |
 | `WP_REDIS_IGNORED_GROUPS`            | `[]`        | Groups that should not be cached between requests in Redis |
 
 <details>
@@ -50,7 +50,8 @@ The Redis Object Cache plugin comes with vast set of configuration options. If y
 | Configuration constant               | Default     | Description                                   |
 | ------------------------------------ | ----------- | --------------------------------------------- |
 | `WP_CACHE_KEY_SALT`                  |             | Deprecated. Replaced by `WP_REDIS_PREFIX` |
-| `WP_REDIS_RETRY_INTERVAL`            |             | The number of milliseconds between retries |
+| `WP_REDIS_FLUSH_TIMEOUT`             | `5`         | Experimental. The timeout in seconds when flushing |
+| `WP_REDIS_RETRY_INTERVAL`            |             | The number of milliseconds between retries (PhpRedis only) |
 | `WP_REDIS_GLOBAL_GROUPS`             | `[]`        | Additional groups that are considered global on multisite networks |
 | `WP_REDIS_METRICS_MAX_TIME`          | `3600`      | The maximum number of seconds metrics should be stored |
 | `WP_REDIS_IGBINARY`                  | `false`     | Whether to use the igbinary PHP extension for serialization |
@@ -69,11 +70,11 @@ The Redis Object Cache plugin comes with vast set of configuration options. If y
 
 Options that exist, but **should not**, **may break without notice** in future releases and **won't receive any support** whatsoever from our team:
 
-| Configuration constant        | Default     | Description                                                         |
-| ----------------------------- | ----------- | ------------------------------------------------------------------- |
+| Configuration constant        | Default     | Description                                                           |
+| ----------------------------- | ----------- | --------------------------------------------------------------------- |
 | `WP_REDIS_GRACEFUL`           | `false`     | Prevents exceptions from being thrown, but will cause data corruption |
-| `WP_REDIS_SELECTIVE_FLUSH`    | `false`     | Uses terribly slow Lua script for flushing                          |
-| `WP_REDIS_UNFLUSHABLE_GROUPS` | `[]`        | Uses terribly slow Lua script to prevent groups from being flushed  |
+| `WP_REDIS_SELECTIVE_FLUSH`    | `false`     | Uses terribly slow Lua script for flushing                            |
+| `WP_REDIS_UNFLUSHABLE_GROUPS` | `[]`        | Uses terribly slow Lua script to prevent groups from being flushed    |
 
 </details>
 

includes/class-plugin.php

@@ -946,13 +946,7 @@ public function do_admin_actions() {
                         );
 
                         if ( $result ) {
-                            try {
-                                $predis = new Predis();
-                                $predis->flush();
-                            } catch ( Exception $exception ) {
-                                // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
-                                error_log( $exception );
-                            }
+                            (new Predis)->flush();
                         }
 
                         /**
@@ -982,13 +976,7 @@ public function do_admin_actions() {
                         $result = $wp_filesystem->delete( WP_CONTENT_DIR . '/object-cache.php' );
 
                         if ( $result ) {
-                            try {
-                                $predis = new Predis();
-                                $predis->flush();
-                            } catch ( Exception $exception ) {
-                                // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
-                                error_log( $exception );
-                            }
+                            (new Predis)->flush();
                         }
 
                         /**
@@ -1534,7 +1522,7 @@ public function on_deactivation( $plugin ) {
                 wp_unschedule_event( $timestamp, 'rediscache_discard_metrics' );
             }
 
-            wp_cache_flush();
+            (new Predis)->flush();
 
             if ( $this->validate_object_cache_dropin() && $this->initialize_filesystem( '', true ) ) {
                 $wp_filesystem->delete( WP_CONTENT_DIR . '/object-cache.php' );

includes/class-predis.php

@@ -22,9 +22,10 @@ class Predis {
     /**
      * Connect to Redis.
      *
+     * @param int|null $read_timeout The read timeout in seconds.
      * @return void
      */
-    public function connect() {
+    public function connect( $read_timeout = null ) {
         // Load bundled Predis library.
         if ( ! class_exists( '\Predis\Client' ) ) {
             require_once WP_REDIS_PLUGIN_PATH . '/dependencies/predis/predis/autoload.php';
@@ -39,7 +40,7 @@ public function connect() {
             'port' => 6379,
             'database' => 0,
             'timeout' => 1,
-            'read_timeout' => 1,
+            'read_timeout' => $read_timeout ?? 1,
         ];
 
         $settings = [
@@ -128,13 +129,26 @@ public function connect() {
     }
 
     /**
-     * Invalidate all items in the cache.
+     * Flushes the entire Redis database using the `WP_REDIS_FLUSH_TIMEOUT`.
      *
-     * @return bool True on success, false on failure.
+     * @param bool $throw_exception Whether to throw exception on error.
+     * @return bool
      */
-    public function flush() {
+    public function flush( $throw_exception = false ) {
+        $flush_timeout = defined( 'WP_REDIS_FLUSH_TIMEOUT' )
+            ? intval(WP_REDIS_FLUSH_TIMEOUT)
+            : 5;
+
         if ( is_null( $this->redis ) ) {
-            $this->connect();
+            try {
+                $this->connect( $flush_timeout );
+            } catch ( Exception $exception ) {
+                if ( $throw_exception ) {
+                    throw $exception;
+                }
+
+                return false;
+            }
         }
 
         if ( defined( 'WP_REDIS_CLUSTER' ) ) {
@@ -143,23 +157,43 @@ public function flush() {
                     $this->redis->flushdb( $master );
                 }
             } catch ( Exception $exception ) {
+                if ( $throw_exception ) {
+                    throw $exception;
+                }
+
                 return false;
             }
-        } else {
-            try {
-                $this->redis->flushdb();
-            } catch ( Exception $exception ) {
-                return false;
+
+            return true;
+        }
+
+        try {
+            $this->redis->flushdb();
+        } catch ( Exception $exception ) {
+            if ( $throw_exception ) {
+                throw $exception;
             }
+
+            return false;
         }
 
         return true;
     }
 
+    /**
+     * Flushes the entire Redis database using the `WP_REDIS_FLUSH_TIMEOUT`
+     * and will throw an exception if anything goes wrong.
+     *
+     * @return bool
+     */
+    public function flushOrFail() {
+        return $this->flush( true );
+    }
+
     /**
      * Builds a clean connection array out of redis clusters array.
      *
-     * @return  array
+     * @return array
      */
     protected function build_cluster_connection_array() {
         $cluster = array_values( WP_REDIS_CLUSTER );

includes/cli/class-commands.php

@@ -173,20 +173,11 @@ public function update_dropin() {
      */
     protected function flush_redis() {
         try {
-            $predis = new Predis();
-            $predis->connect();
+            return (new Predis)->flushOrFail();
         } catch ( Exception $exception ) {
-            return $exception->getMessage();
-        }
+            error_log( $exception ); // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
 
-        try {
-            $predis->flush();
-        } catch ( Exception $exception ) {
-            // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
-            error_log( $exception );
+            return $exception->getMessage();
         }
-
-        return true;
     }
-
 }