diff --git a/core/lib/Drupal/Core/Extension/SchemaInstaller.php b/core/lib/Drupal/Core/Extension/SchemaInstaller.php
index a18198e8d8..1aff3add12 100644
--- a/core/lib/Drupal/Core/Extension/SchemaInstaller.php
+++ b/core/lib/Drupal/Core/Extension/SchemaInstaller.php
@@ -12,27 +12,6 @@
  */
 class SchemaInstaller implements SchemaInstallerInterface {
 
-  /**
-   * Statically cached schema data.
-   *
-   * @var array
-   */
-  protected $schema;
-
-  /**
-   * Statically cached complete schema data.
-   *
-   * @var array
-   */
-  protected $completeSchema;
-
-  /**
-   * A static cache of schema currentVersions per module.
-   *
-   * @var array
-   */
-  protected $allVersions = [];
-
   /**
    * A static cache of current module schema currentVersions.
    *
@@ -101,7 +80,7 @@ public function __construct(ModuleHandlerInterface $module_handler, CacheBackend
    * {@inheritdoc}
    */
   public function getInstalledVersion($module) {
-    $this->initCurrentVersions();
+    $this->ensureInitialized();
     return $this->currentVersions[$module] ?? static::UNINSTALLED;
   }
 
@@ -109,7 +88,7 @@ public function getInstalledVersion($module) {
    * {@inheritdoc}
    */
   public function getInstalledVersions() {
-    $this->initCurrentVersions();
+    $this->ensureInitialized();
     return $this->currentVersions;
   }
 
@@ -117,10 +96,9 @@ public function getInstalledVersions() {
    * {@inheritdoc}
    */
   public function resetCache() {
-    $this->currentVersions = [];
-    if (!$this->currentVersions = $this->keyValue->get('system.schema')->getAll()) {
-      $this->currentVersions = [];
-    }
+    // Setting to NULL to re-read data on first use in initCurrentVersions().
+    $this->currentVersions = NULL;
+    return $this;
   }
 
   /**
@@ -128,9 +106,7 @@ public function resetCache() {
    */
   public function setInstalledVersion($module, $version) {
     $this->keyValue->get('system.schema')->set($module, $version);
-    // Reset the static cache of module schema currentVersions.
-    $this->resetCache();
-    $this->getInstalledVersions();
+    $this->resetCache()->ensureInitialized();
   }
 
   /**
@@ -194,7 +170,7 @@ public function getSchema($module, $table = NULL) {
    *   tables and fields to improve performance of serialize() and
    *   unserialize(). Defaults to TRUE.
    */
-  private function initialize(array &$schema, $module, $remove_descriptions = TRUE) {
+  protected function initialize(array &$schema, $module, $remove_descriptions = TRUE) {
     // Set the name and module key for all tables.
     foreach ($schema as $name => &$table) {
       if (empty($table['module'])) {
@@ -213,9 +189,11 @@ private function initialize(array &$schema, $module, $remove_descriptions = TRUE
   }
 
   /**
-   * Initialize the schema versions.
+   * Check if the static cache populated and initialize it if not.
+   *
+   * @see resetCache()
    */
-  protected function initCurrentVersions() {
+  protected function ensureInitialized() {
     if (is_null($this->currentVersions)) {
       if (!$this->currentVersions = $this->keyValue->get('system.schema')->getAll()) {
         $this->currentVersions = [];
diff --git a/core/lib/Drupal/Core/Extension/SchemaInstallerInterface.php b/core/lib/Drupal/Core/Extension/SchemaInstallerInterface.php
index 02ac1d1820..9c7f99f3e8 100644
--- a/core/lib/Drupal/Core/Extension/SchemaInstallerInterface.php
+++ b/core/lib/Drupal/Core/Extension/SchemaInstallerInterface.php
@@ -18,9 +18,9 @@ interface SchemaInstallerInterface {
    * @param string $module
    *   A module name.
    *
-   * @return string|int|array
-   *   The currently installed schema version, static::UNINSTALLED if the
-   *   module is not installed, or an array for all modules.
+   * @return string|int
+   *   The currently installed schema version or static::UNINSTALLED if the
+   *   module is not installed.
    */
   public function getInstalledVersion($module);
 
@@ -34,6 +34,8 @@ public function getInstalledVersions();
 
   /**
    * Reset the version cache.
+   *
+   * @return $this
    */
   public function resetCache();
 
diff --git a/core/modules/system/tests/src/Functional/UpdateSystem/UpdateScriptTest.php b/core/modules/system/tests/src/Functional/UpdateSystem/UpdateScriptTest.php
index d57446e05e..748277b72f 100644
--- a/core/modules/system/tests/src/Functional/UpdateSystem/UpdateScriptTest.php
+++ b/core/modules/system/tests/src/Functional/UpdateSystem/UpdateScriptTest.php
@@ -143,7 +143,8 @@ public function testRequirements() {
     // successfully.
     $this->drupalLogin($this->updateUser);
     $update_script_test_config->set('requirement_type', REQUIREMENT_WARNING)->save();
-    \Drupal::service('schema_installer')->setInstalledVersion('update_script_test', \Drupal::service('schema_installer')->getInstalledVersion('update_script_test') - 1);
+    $schema_installer = \Drupal::service('schema_installer');
+    $schema_installer->setInstalledVersion('update_script_test', $schema_installer->getInstalledVersion('update_script_test') - 1);
     $this->drupalGet($this->updateUrl, ['external' => TRUE]);
     $this->assertText('This is a requirements warning provided by the update_script_test module.');
     $this->clickLink('try again');
@@ -486,15 +487,13 @@ public function testSuccessfulUpdateFunctionality() {
     $final_maintenance_mode = $this->container->get('state')->get('system.maintenance_mode');
     $this->assertEqual($final_maintenance_mode, $initial_maintenance_mode, 'Maintenance mode should not have changed after database updates.');
 
-    // Reset the static cache to ensure we have the most current setting.
+    // Reset the static cache to get the current schema after running updates.
     $schema_installer = \Drupal::service('schema_installer');
     $this->assertTrue($schema_installer instanceof SchemaInstallerInterface);
-    $schema_installer->resetCache();
-    $schema_version = $schema_installer->getInstalledVersion('update_script_test');
+    $schema_version = $schema_installer->resetCache()->getInstalledVersion('update_script_test');
     $this->assertEqual($schema_version, 8001, 'update_script_test schema version is 8001 after updating.');
 
     // Set the installed schema version to one less than the current update.
-    $schema_installer->resetCache();
     $schema_installer->setInstalledVersion('update_script_test', $schema_version - 1);
     $schema_version = $schema_installer->getInstalledVersion('update_script_test');
     $this->assertEqual($schema_version, 8000, 'update_script_test schema version overridden to 8000.');
@@ -550,16 +549,13 @@ public function testSuccessfulMultilingualUpdateFunctionality() {
     $config->set('url.prefixes.en', 'en');
     $config->save();
 
-    // Reset the static cache to ensure we have the most current setting.
     /** @var \Drupal\Core\Extension\SchemaInstallerInterface $schema_installer */
     $schema_installer = \Drupal::service('schema_installer');
-    $schema_installer->resetCache();
     $schema_version = $schema_installer->getInstalledVersion('update_script_test');
     $this->assertEqual($schema_version, 8001, 'update_script_test schema version is 8001 after updating.');
 
     // Set the installed schema version to one less than the current update.
     $schema_installer->setInstalledVersion('update_script_test', $schema_version - 1);
-    $schema_installer->resetCache();
     $schema_version = $schema_installer->getInstalledVersion('update_script_test');
     $this->assertEqual($schema_version, 8000, 'update_script_test schema version overridden to 8000.');
 
@@ -599,7 +595,6 @@ protected function runUpdates($maintenance_mode) {
 
     // Set the installed schema version to one less than the current update.
     $schema_installer->setInstalledVersion('update_script_test', $schema_version - 1);
-    $schema_installer->resetCache();
     $schema_version = $schema_installer->getInstalledVersion('update_script_test');
     $this->assertEqual($schema_version, 8000, 'update_script_test schema version overridden to 8000.');
 
diff --git a/core/tests/Drupal/FunctionalTests/Update/UpdatePathTestBaseTest.php b/core/tests/Drupal/FunctionalTests/Update/UpdatePathTestBaseTest.php
index ac19cc44aa..4c1986124d 100644
--- a/core/tests/Drupal/FunctionalTests/Update/UpdatePathTestBaseTest.php
+++ b/core/tests/Drupal/FunctionalTests/Update/UpdatePathTestBaseTest.php
@@ -38,7 +38,6 @@ public function testDatabaseLoaded() {
     $schema_installer = \Drupal::service('schema_installer');
     foreach (['user' => 8100, 'node' => 8700, 'system' => 8805, 'update_test_schema' => 8000] as $module => $schema) {
       $this->assertEqual($schema_installer->getInstalledVersion($module), $schema, new FormattableMarkup('Module @module schema is @schema', ['@module' => $module, '@schema' => $schema]));
-
     }
 
     // Ensure that all {router} entries can be unserialized. If they cannot be
diff --git a/core/tests/Drupal/KernelTests/KernelTestBase.php b/core/tests/Drupal/KernelTests/KernelTestBase.php
index 4b5752c15f..be0175862f 100644
--- a/core/tests/Drupal/KernelTests/KernelTestBase.php
+++ b/core/tests/Drupal/KernelTests/KernelTestBase.php
@@ -699,7 +699,7 @@ protected function installConfig($modules) {
    *   If $module is not enabled or the table schema cannot be found.
    */
   protected function installSchema($module, $tables) {
-    // drupal_get_module_schema() is technically able to install a schema
+    // Schema installer is technically able to install a schema
     // of a non-enabled module, but its ability to load the module's .install
     // file depends on many other factors. To prevent differences in test
     // behavior and non-reproducible test failures, we only allow the schema of