wp-db.php on line 1704 error

Hi guys, i try run a wodpress site with almost a 34k pages,
i try go to via admin edit.php?post_type=page and just simply browse all pages or add new i get error

Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 64 bytes) in / REMOVED /wp-includes/wp-db.php on line 1704

I use a vps with a 2gb memory 2 cpus, and i setup a php ini for 1024MB and wp-config also for this value,

any idea how to run very big wodpress site, what i need to do ? more ram ? tnx