Allowed memory size exhausted with 26k GF entries

I have to increase Memory Limit to fetch 26,000 GF entries as a chart.

I already placed following code in the WP Config file but it didn’t change anything:

define( 'WP_MAX_MEMORY_LIMIT' , '512M' );
define( 'WP_MEMORY_LIMIT' , '512M' );

I still get the same error:
Fatal error: Allowed memory size of 536870912 bytes exhausted (tried to allocate 33554440 bytes) in /…/wp-includes/wp-db.php on line 1996

This is on line 1996

if ( $this->use_mysqli && $this->result instanceof mysqli_result ) {
				while ( $row = mysqli_fetch_object( $this->result ) ) {
					$this->last_result[ $num_rows ] = $row;
					$num_rows++;
				}