[Bitrix\Main\DB\ConnectionException] 
Mysql connect error [localhost]: (2006) MySQL server has gone away (400)
/home/bitrix/www/bitrix/modules/main/lib/db/mysqliconnection.php:65
#0: Bitrix\Main\DB\MysqliConnection->connectInternal()
	/home/bitrix/www/bitrix/modules/main/lib/db/mysqliconnection.php:122
#1: Bitrix\Main\DB\MysqliConnection->queryInternal(string, array, NULL)
	/home/bitrix/www/bitrix/modules/main/lib/db/connection.php:330
#2: Bitrix\Main\DB\Connection->query(string, NULL)
	/home/bitrix/www/bitrix/modules/main/lib/db/connection.php:379
#3: Bitrix\Main\DB\Connection->queryExecute(string)
	/home/bitrix/www/bitrix/php_interface/after_connect_d7.php:3
#4: include(string)
	/home/bitrix/www/bitrix/modules/main/lib/db/connection.php:921
#5: Bitrix\Main\DB\Connection->afterConnected()
	/home/bitrix/www/bitrix/modules/main/lib/db/mysqliconnection.php:81
#6: Bitrix\Main\DB\MysqliConnection->connectInternal()
	/home/bitrix/www/bitrix/modules/main/lib/db/mysqliconnection.php:122
#7: Bitrix\Main\DB\MysqliConnection->queryInternal(string, NULL, NULL)
	/home/bitrix/www/bitrix/modules/main/lib/db/connection.php:330
#8: Bitrix\Main\DB\Connection->query(string, NULL, integer, integer)
	/home/bitrix/www/bitrix/modules/main/lib/db/connection.php:358
#9: Bitrix\Main\DB\Connection->queryScalar(string)
	/home/bitrix/www/bitrix/modules/security/lib/session.php:114
#10: Bitrix\Security\SessionTable::lock(string, integer)
	/home/bitrix/www/bitrix/modules/security/classes/general/session_db.php:52
#11: CSecuritySessionDB::read(string)
	
#12: session_start()
	/home/bitrix/www/bitrix/modules/main/include.php:281
#13: require_once(string)
	/home/bitrix/www/bitrix/modules/main/include/prolog_before.php:14
#14: require_once(string)
	/home/bitrix/www/bitrix/modules/main/include/prolog.php:10
#15: require_once(string)
	/home/bitrix/www/bitrix/header.php:1
#16: require(string)
	/home/bitrix/www/category/index.php:2
#17: include_once(string)
	/home/bitrix/www/bitrix/modules/main/include/urlrewrite.php:159
#18: include_once(string)
	/home/bitrix/www/bitrix/urlrewrite.php:2

Fatal error: Uncaught Bitrix\Main\DB\SqlQueryException: Mysql query error: (2006) MySQL server has gone away in /home/bitrix/www/bitrix/modules/main/lib/db/mysqliconnection.php:137 Stack trace: #0 /home/bitrix/www/bitrix/modules/main/lib/db/mysqlcommonconnection.php(136): Bitrix\Main\DB\MysqliConnection->queryInternal('SELECT * FROM `...') #1 /home/bitrix/www/bitrix/modules/main/lib/db/connection.php(716): Bitrix\Main\DB\MysqlCommonConnection->getTableFields('b_sec_session') #2 /home/bitrix/www/bitrix/modules/main/lib/db/sqlhelper.php(395): Bitrix\Main\DB\Connection->getTableField('b_sec_session', 'SESSION_ID') #3 /home/bitrix/www/bitrix/modules/main/lib/orm/data/datamanager.php(1198): Bitrix\Main\DB\SqlHelper->prepareAssignment('b_sec_session', 'SESSION_ID', 'VbW9OherxZBJbSR...') #4 /home/bitrix/www/bitrix/modules/security/classes/general/session_db.php(92): Bitrix\Main\ORM\Data\DataManager::delete(Array) #5 [internal function]: CSecuritySessionDB::write('VbW9OherxZBJbSR...', '') #6 [internal function]: session_write_clo in /home/bitrix/www/bitrix/modules/main/lib/db/mysqliconnection.php on line 137