MDL-83753 redis: Allow for configurable max retries setting

config-dist.php

@@ -371,6 +371,7 @@
 //      $CFG->session_redis_lock_retry = 100;                // Optional wait between lock attempts in ms, default is 100.
 //                                                           // After 5 seconds it will throttle down to once per second.
 //      $CFG->session_redis_connection_timeout = 3;          // Optional, default is 3.
+//      $CFG->session_redis_maxretries = 3;                  // Optional, default is 3.
 //
 //      Use the igbinary serializer instead of the php default one. Note that phpredis must be compiled with
 //      igbinary support to make the setting to work. Also, if you change the serializer you have to flush the database!

lib/classes/session/redis.php

@@ -106,7 +106,7 @@ class redis extends handler implements SessionHandlerInterface {
     protected bool $clustermode = false;
 
     /** @var int Maximum number of retries for cache store operations. */
-    const MAX_RETRIES = 5;
+    protected int $maxretries = 3;
 
     /** @var int $firstaccesstimeout The initial timeout (seconds) for the first browser access without login. */
     protected int $firstaccesstimeout = 180;
@@ -208,6 +208,10 @@ public function __construct() {
             $this->connectiontimeout = (int)$CFG->session_redis_connection_timeout;
         }
 
+        if (isset($CFG->session_redis_max_retries)) {
+            $this->maxretries = (int)$CFG->session_redis_max_retries;
+        }
+
         $this->clock = di::get(clock::class);
     }
 
@@ -282,10 +286,10 @@ public function init(): bool {
             }
         }
 
-        // MDL-59866: Add retries for connections (up to 5 times) to make sure it goes through.
+        // Add retries for connections to make sure it goes through.
         $counter = 1;
         $exceptionclass = $this->clustermode ? 'RedisClusterException' : 'RedisException';
-        while ($counter <= self::MAX_RETRIES) {
+        while ($counter <= $this->maxretries) {
             $this->connection = null;
             // Make a connection to Redis server(s).
             try {
@@ -387,7 +391,7 @@ public function init(): bool {
                 return true;
             } catch (RedisException | RedisClusterException $e) {
                 $redishost = $this->clustermode ? implode(',', $this->host) : $server . ':' . $port;
-                $logstring = "Failed to connect (try {$counter} out of " . self::MAX_RETRIES . ") to Redis ";
+                $logstring = "Failed to connect (try {$counter} out of " . $this->maxretries . ") to Redis ";
                 $logstring .= "at ". $redishost .", the error returned was: {$e->getMessage()}";
                 debugging($logstring);
             }

lib/tests/session/redis_test.php

@@ -360,8 +360,8 @@ public function test_exception_when_connection_attempts_exceeded(): void {
         // Therefore, to get the host, we need to explode it.
         list($host, ) = explode(':', TEST_SESSION_REDIS_HOST);
 
-        $expected = "Failed to connect (try 5 out of 5) to Redis at $host:111111";
-        $this->assertDebuggingCalledCount(5);
+        $expected = "Failed to connect (try 3 out of 3) to Redis at $host:111111";
+        $this->assertDebuggingCalledCount(3);
         $this->assertStringContainsString($expected, $actual);
     }