php - PDO do not able to fetch huge data -

i'm trying fetch data 1 mysql table more 5 m rows , 50 gb total size, use pdo it. looks like

$urlscontent = $db->query('select url_hash,content sy_search_site_stat'); while($result = $urlscontent->fetch()) {     ... write content files;     ... echo content hashes; } 

but when run without limit in console, output "killed" after several minutes of working. when write limit sql query, works fine. there particular restrictions on pdo?

$pdo->setattribute(pdo::mysql_attr_use_buffered_query, false); 

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