Fix GravityForms GFFormsModel::get_custom_field_names() for large numbers of posts and post meta by limiting to post_type='page'

fix-gravity-forms.php

<?php

/**
 * Class Fix_Gravity_Forms
 */
class Fix_Gravity_Forms {

	const POST_TYPE = 'page';

	const SQL_MARKER = "WHERE meta_key NOT BETWEEN '_' AND '_z'";

	static function on_load() {
		add_filter(
			'gform_field_standard_settings',
			[ __CLASS__, '_gform_field_standard_settings' ]
		);
	}

	/**
	 * Wait to attach the query filter to just before we need it
	 * and remove just after we use it.
	 *
	 * @param int $number
	 */
	static function _gform_field_standard_settings( $number ) {
		switch ( $number ) {
			case 650:
				add_filter( 'query', [ __CLASS__, '_query' ] );
				break;
			case 700:
				remove_filter( 'query', [ __CLASS__, '_query' ] );
				break;
		}
	}

	/**
	 * @param string $query
	 * @return string
	 */
	static function _query( $query ) {
		do {
			if ( 'S' !== $query[ 0 ] ) {
				break;
			}
			if ( false === strpos( $query, self::SQL_MARKER ) ) {
				break;
			}
			global $wpdb;
			$join_sql = " JOIN {$wpdb->posts} ON {$wpdb->posts}.ID={$wpdb->postmeta}.post_id" .
			            " AND {$wpdb->posts}.post_type='%s'";
			$query = str_replace(
				self::SQL_MARKER,
				$wpdb->prepare( $join_sql, self::POST_TYPE ) . self::SQL_MARKER,
				$query
			);

		} while ( false );
		return $query;
	}


}
Fix_Gravity_Forms::on_load();