Support persistent connections via WP_REDIS_PERSISTENT (#633)

Author: fx2300

README.md

@@ -53,6 +53,7 @@ The Redis Object Cache plugin comes with vast set of configuration options. If y
 | `WP_REDIS_SSL_CONTEXT`               | `[]`        | TLS connection options for `tls` or `rediss` scheme |
 | `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_PERSISTENT`                | `false`     | Whether to persistent connections. Optionally, accepts non-empty connection identifier string. |
 | `WP_REDIS_GLOBAL_GROUPS`             | `[]`        | Additional groups that are considered global on multisite networks |
 | `WP_REDIS_CHART_COLOR`               |             | Override admin metrics chart color using a hex value (`#RGB` or `#RRGGBB`) |
 | `WP_REDIS_METRICS_MAX_TIME`          | `3600`      | The maximum number of seconds metrics should be stored |

includes/diagnostics.php

@@ -62,6 +62,7 @@
     $info['Timeout'] = $wp_object_cache->diagnostics['timeout'] ?? false;
     $info['Read Timeout'] = $wp_object_cache->diagnostics['read_timeout'] ?? false;
     $info['Retry Interval'] = $wp_object_cache->diagnostics['retry_interval'] ?? false;
+    $info['Persistent'] = $wp_object_cache->diagnostics['persistent'] ?? false;
 }
 
 $constants = [
@@ -76,6 +77,7 @@
     'WP_REDIS_TIMEOUT',
     'WP_REDIS_READ_TIMEOUT',
     'WP_REDIS_RETRY_INTERVAL',
+    'WP_REDIS_PERSISTENT',
     'WP_REDIS_SERVERS',
     'WP_REDIS_CLUSTER',
     'WP_REDIS_SHARDS',

includes/object-cache.php

@@ -640,6 +640,7 @@ protected function build_parameters() {
             'timeout',
             'read_timeout',
             'retry_interval',
+            'persistent',
         ];
 
         foreach ( $settings as $setting ) {
@@ -657,10 +658,35 @@ protected function build_parameters() {
         $this->diagnostics[ 'timeout' ] = $parameters[ 'timeout' ];
         $this->diagnostics[ 'read_timeout' ] = $parameters[ 'read_timeout' ];
         $this->diagnostics[ 'retry_interval' ] = $parameters[ 'retry_interval' ];
+        $this->diagnostics[ 'persistent' ] = $parameters[ 'persistent' ];
 
         return $parameters;
     }
 
+    /**
+     * Build the identifier persistent connections are pooled by.
+     *
+     * `WP_REDIS_PERSISTENT` carries both answers: any truthy value turns persistence on, and a
+     * non-empty string additionally names the pool. Anything else falls back to the default.
+     *
+     * PhpRedis, Relay and Credis keep one persistent connection per host, port and identifier.
+     * Whatever is applied *after* connecting is part of that connection's state and therefore
+     * has to be part of the identifier: `select()` is only called for a non-zero database, so
+     * two sites sharing a pool would otherwise silently inherit whichever database the other
+     * one selected last. That is why the default carries the database, and why an identifier
+     * given by hand is the caller's to keep distinct.
+     *
+     * @param  array $parameters Connection parameters built by the `build_parameters` method.
+     * @return string
+     */
+    protected function build_persistent_id( $parameters ) {
+        if ( is_string( $parameters['persistent'] ) && $parameters['persistent'] !== '' ) {
+            return $parameters['persistent'];
+        }
+
+        return sprintf( 'wp-db%s', $parameters['database'] );
+    }
+
     /**
      * Connect to Redis using the PhpRedis (PECL) extension.
      *
@@ -709,7 +735,7 @@ protected function connect_using_phpredis( $parameters ) {
                 'host' => $parameters['host'],
                 'port' => $parameters['port'],
                 'timeout' => $parameters['timeout'],
-                '',
+                'persistent_id' => $parameters['persistent'] ? $this->build_persistent_id( $parameters ) : '',
                 'retry_interval' => (int) $parameters['retry_interval'],
             ];
 
@@ -734,7 +760,10 @@ protected function connect_using_phpredis( $parameters ) {
                 $args['port'] = -1;
             }
 
-            call_user_func_array( [ $this->redis, 'connect' ], array_values( $args ) );
+            call_user_func_array(
+                [ $this->redis, $parameters['persistent'] ? 'pconnect' : 'connect' ],
+                array_values( $args )
+            );
 
             if ( isset( $parameters['password'] ) ) {
                 $args['password'] = $parameters['password'];
@@ -779,7 +808,7 @@ protected function connect_using_relay( $parameters ) {
                 'host' => $parameters['host'],
                 'port' => $parameters['port'],
                 'timeout' => $parameters['timeout'],
-                '',
+                'persistent_id' => $parameters['persistent'] ? $this->build_persistent_id( $parameters ) : '',
                 'retry_interval' => (int) $parameters['retry_interval'],
             ];
 
@@ -802,7 +831,10 @@ protected function connect_using_relay( $parameters ) {
                 $args['port'] = -1;
             }
 
-            call_user_func_array( [ $this->redis, 'connect' ], array_values( $args ) );
+            call_user_func_array(
+                [ $this->redis, $parameters['persistent'] ? 'pconnect' : 'connect' ],
+                array_values( $args )
+            );
 
             if ( isset( $parameters['password'] ) ) {
                 $args['password'] = $parameters['password'];
@@ -1049,7 +1081,7 @@ protected function connect_using_credis( $parameters ) {
                 'host' => $parameters['scheme'] === 'unix' ? $parameters['path'] : $parameters['host'],
                 'port' => $parameters['port'],
                 'timeout' => $parameters['timeout'],
-                'persistent' => '',
+                'persistent' => $parameters['persistent'] ? $this->build_persistent_id( $parameters ) : '',
                 'database' => $parameters['database'],
                 'password' => isset( $parameters['password'] ) ? $parameters['password'] : null,
             ];