Fatal error: Allowed memory size

Hello guys,

I’m receiving this error when I try to enter in the settings page “Country IP Specific Redirections”:

Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 82 bytes) in /home/username/public_html/wp-includes/wp-db.php on line 1906

Any idea how to fix this?

I tried to add in wp-config.php the line:
define( 'WP_MEMORY_LIMIT', '256M' );

But didn’t worked… only:
define( 'WP_MEMORY_LIMIT', '1024M' );

But with 1024M my website becomes very slowwww…

Thanks!