core/lib/Drupal/Core/Cache/DatabaseBackend.php | 44 ++++++++++++++++++++++++++
 core/modules/system/system.install             | 11 +++++++
 2 files changed, 55 insertions(+)

diff --git a/core/lib/Drupal/Core/Cache/DatabaseBackend.php b/core/lib/Drupal/Core/Cache/DatabaseBackend.php
index d53c51c..da1ee6d 100644
--- a/core/lib/Drupal/Core/Cache/DatabaseBackend.php
+++ b/core/lib/Drupal/Core/Cache/DatabaseBackend.php
@@ -17,6 +17,16 @@
 class DatabaseBackend implements CacheBackendInterface {
 
   /**
+   * The megabytes of disk space this cache bin is allowed to use.
+   *
+   * @todo Bikeshed the size limit.
+   * @todo Make configurable per-bin.
+   *
+   * @var int
+   */
+  protected static $boundedSizeMegabytes = 10;
+
+  /**
    * @var string
    */
   protected $bin;
@@ -326,6 +336,34 @@ public function invalidateAll() {
    */
   public function garbageCollection() {
     try {
+
+      $connection_info = $this->connection->getConnectionOptions();
+      if ($connection_info['driver'] === 'mysql') {
+        $query = "SELECT round(((`data_length` + `index_length`) / 1024 / 1024), 2) AS `size` FROM `information_schema`.`TABLES`
+    WHERE (`TABLE_SCHEMA` = '" . $connection_info['database'] . "')
+    AND (`TABLE_NAME` = '{" . $this->bin. "}')";
+        $results = $this->connection->query($query);
+        $size = (float) $results->fetchField();
+
+        if ($size > static::$boundedSizeMegabytes) {
+          $query = $this->connection->select($this->bin);
+          $query->addExpression('COUNT(bounded_id)', 'bounded_id');
+          $row_count = (int) $query->execute()->fetchField();
+
+          $average_row_size = $size / $row_count;
+
+          $desired_reduction = $size - static::$boundedSizeMegabytes;
+          $estimated_number_of_rows_to_delete = round($desired_reduction / $average_row_size);
+
+          // Note that we cannot use $this->connection->delete() because that does not support order by …
+          $this->connection->query('DELETE FROM {' . $this->bin . '} ORDER BY bounded_id ASC LIMIT ' . $estimated_number_of_rows_to_delete)
+            ->execute();
+        }
+      }
+      else {
+        // @todo what about non-mysql???
+      }
+
       $this->connection->delete($this->bin)
         ->condition('expire', Cache::PERMANENT, '<>')
         ->condition('expire', REQUEST_TIME, '<')
@@ -469,11 +507,17 @@ public function schemaDefinition() {
           'length' => 255,
           'not null' => TRUE,
         ],
+        'bounded_id' => [
+          'type' => 'serial',
+        ],
       ],
       'indexes' => [
         'expire' => ['expire'],
       ],
       'primary key' => ['cid'],
+      'unique keys' => [
+        'bounded_id' => ['bounded_id'],
+      ]
     ];
     return $schema;
   }
diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index 90e6291..e0c9633 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -1965,3 +1965,14 @@ function system_update_8400(&$sandbox) {
 
   $sandbox['#finished'] = $sandbox['current'] == $sandbox['max'];
 }
+
+/**
+ * Delete all cache_* tables. They are recreated on demand with the new schema.
+ */
+function system_update_8401() {
+  foreach (\Drupal\Core\Cache\Cache::getBins() as $bin => $cache_backend) {
+    if ($cache_backend instanceof \Drupal\Core\Cache\DatabaseBackend) {
+      db_drop_table("cache_$bin");
+    }
+  }
+}