TP5.1 uses session to report errors

Session::set ("username",$username) set in this way in the controller;
also introduces use think\ facade\ Session and use think\ facade\ Cookie ;
but why is this wrong?

configsession.php

Mar.16,2021

you need to create your own tmp directory pit manually when you know why

MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b9e605-2eb79.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b9e605-2eb79.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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