Issue #1969846 by rootatwc: Convert session_write_interval() to settings.

core/includes/session.inc

@@ -169,7 +169,7 @@ function _drupal_session_write($sid, $value) {
 
     // For performance reasons, do not update the sessions table, unless
     // $_SESSION has changed or more than 180 has passed since the last update.
-    if ($is_changed || !isset($user->timestamp) || REQUEST_TIME - $user->timestamp > variable_get('session_write_interval', 180)) {
+    if ($is_changed || !isset($user->timestamp) || REQUEST_TIME - $user->timestamp > settings()->get('session_write_interval', 180)) {
       // Either ssid or sid or both will be added from $key below.
       $fields = array(
         'uid' => $user->uid,
@@ -206,7 +206,7 @@ function _drupal_session_write($sid, $value) {
     }
 
     // Likewise, do not update access time more than once per 180 seconds.
-    if ($user->uid && REQUEST_TIME - $user->access > variable_get('session_write_interval', 180)) {
+    if ($user->uid && REQUEST_TIME - $user->access > settings()->get('session_write_interval', 180)) {
       db_update('users')
         ->fields(array(
           'access' => REQUEST_TIME

core/modules/system/lib/Drupal/system/Tests/Session/SessionTest.php

@@ -228,7 +228,13 @@ function testSessionWrite() {
     $this->assertEqual($times4->timestamp, $times3->timestamp, 'Sessions table was not updated.');
 
     // Force updating of users and sessions table once per second.
-    variable_set('session_write_interval', 0);
+    $this->settingsSet('session_write_interval', 0);
+    // Write that value also into the test settings.php file.
+    $settings['settings']['session_write_interval'] = (object) array(
+      'value' => 0,
+      'required' => TRUE,
+    );
+    $this->writeSettings($settings);
     $this->drupalGet('');
     $times5 = db_query($sql, array(':uid' => $user->uid))->fetchObject();
     $this->assertNotEqual($times5->access, $times4->access, 'Users table was updated.');

sites/default/default.settings.php

@@ -451,6 +451,14 @@
  */
 # $settings['mixed_mode_sessions'] = TRUE;
 
+/**
+ * Session write interval:
+ *
+ * Set the minimum interval between each session write to database.
+ * For performance reasons it defaults to 180.
+ */
+# $settings['session_write_interval'] = 180;
+
 /**
  * Base URL (optional).
  *