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Drupal\Core\Database\DatabaseExceptionWrapper: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away: CREATE TABLE {cache_menu} ( `cid` VARCHAR(255) CHARACTER SET ascii BINARY NOT NULL DEFAULT '' COMMENT 'Primary Key: Unique cache ID.', `data` LONGBLOB NULL DEFAULT NULL COMMENT 'A collection of data to cache.', `expire` INT NOT NULL DEFAULT 0 COMMENT 'A Unix timestamp indicating when the cache entry should expire, or -1 for never.', `created` DECIMAL(14, 3) NOT NULL DEFAULT 0 COMMENT 'A timestamp with millisecond precision indicating when the cache entry was created.', `serialized` SMALLINT NOT NULL DEFAULT 0 COMMENT 'A flag to indicate whether content is serialized (1) or not (0).', `tags` LONGTEXT NULL DEFAULT NULL COMMENT 'Space-separated list of cache tags for this entry.', `checksum` VARCHAR(255) CHARACTER SET ascii COLLATE ascii_general_ci NOT NULL COMMENT 'The tag invalidation checksum when this entry was saved.', PRIMARY KEY (`cid`), INDEX `expire` (`expire`), INDEX `created` (`created`) ) ENGINE = InnoDB DEFAULT CHARACTER SET utf8mb4 COMMENT 'Storage for the cache API.'; Array ( ) in Drupal\Core\Cache\CacheCollector->updateCache() (line 266 of core/lib/Drupal/Core/Cache/CacheCollector.php). 
Drupal\Core\Cache\CacheCollector->updateCache() (Line: 327)
Drupal\Core\Cache\CacheCollector->destruct() (Line: 51)
Drupal\Core\EventSubscriber\KernelDestructionSubscriber->onKernelTerminate(Object, 'kernel.terminate', Object)
call_user_func(Array, Object, 'kernel.terminate', Object) (Line: 111)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch('kernel.terminate', Object) (Line: 88)
Symfony\Component\HttpKernel\HttpKernel->terminate(Object, Object) (Line: 32)
Stack\StackedHttpKernel->terminate(Object, Object) (Line: 671)
Drupal\Core\DrupalKernel->terminate(Object, Object) (Line: 22)

Uncaught exception thrown in shutdown function.

Drupal\Core\Database\DatabaseExceptionWrapper: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away: DELETE FROM {semaphore} WHERE value = :db_condition_placeholder_0; Array ( [:db_condition_placeholder_0] => 1565671252674096364910e9.68449764 ) in _drupal_shutdown_function() (line 1043 of /var/www/html/new_trainee/core/includes/bootstrap.inc). 

_drupal_shutdown_function()