Wordpress — why stop wp_insert_post()? -

trying load 4.5 million records in wordpress. import stops @ ~ 90 thousands. why so? if remove function wp_insert_post(), cycle runs (89 times). no errors in logs. please me

<? require_once('../../wp-load.php'); $host='host'; $database='database'; $user='user'; $pswd='pswd'; $dbh = mysqli_connect($host, $user, $pswd) or die("Не могу соединиться с mysql."); mysqli_select_db($dbh, $database) or die("Не могу подключиться к базе."); ($l = 0; $l <= 89; $l++) {     $limit = $l * 50000;     $sql = "select `npi`, `provider_last_name_legal_name`, `provider_first_name`, `provider_middle_name`, `provider_name_prefix_text`, `provider_name_suffix_text`, `provider_first_line_business_mailing_address`, `provider_second_line_business_mailing_address`, `provider_business_practice_location_address_city_name`, `provider_business_practice_location_address_state_name`, `provider_business_practice_location_address_postal_code`, `provider_business_practice_location_address_telephone_number`, `provider_business_practice_location_address_fax_number`, `provider_gender_code`, `provider_first_line_business_practice_location_address` `npi` `used` != 1 , `provider_last_name_legal_name` != ''  limit ".$limit.", 50000";     $res = mysqli_query($dbh, $sql);     $i = 0;     while ($row = mysqli_fetch_array($res, mysqli_assoc)) {         $post_title = $row['provider_first_name'] . ' ' . $row['provider_middle_name'] . ' ' . $row['provider_last_name_legal_name'];         $defaults = array(             'post_status' => 'publish',             'post_type' => 'doctor',             'post_author' => 1,             'post_title' => $post_title         );         /*         $post_id = wp_insert_post($defaults, $wp_error);         update_post_meta($post_id, 'npi_number', $row['npi']);         update_post_meta($post_id, 'provider_name_prefix_text', $row['provider_name_prefix_text']);         update_post_meta($post_id, 'provider_name_prefix_text', $row['provider_name_prefix_text']);         update_post_meta($post_id, 'provider_name_suffix_text', $row['provider_name_suffix_text']);         update_post_meta($post_id, 'provider_first_line_business_mailing_address', $row['provider_first_line_business_mailing_address']);         update_post_meta($post_id, 'provider_second_line_business_mailing_address', $row['provider_second_line_business_mailing_address']);         update_post_meta($post_id, 'provider_business_practice_location_address_city_name', $row['provider_business_practice_location_address_city_name']);         update_post_meta($post_id, 'provider_business_practice_location_address_state_name', $row['provider_business_practice_location_address_state_name']);         update_post_meta($post_id, 'zip', $row['provider_business_practice_location_address_postal_code']);         update_post_meta($post_id, 'provider_business_practice_location_address_telephone_number', $row['provider_business_practice_location_address_telephone_number']);         update_post_meta($post_id, 'provider_business_practice_location_address_fax_number', $row['provider_business_practice_location_address_fax_number']);         update_post_meta($post_id, 'provider_gender_code', $row['provider_gender_code']);         update_post_meta($post_id, 'provider_first_line_business_practice_location_address', $row['provider_first_line_business_practice_location_address']);         update_post_meta($post_id, 'is_npi', '1');         */         $i++;         unset($post_title, $row, $post_id, $defaults);     }     echo 'cycle: '.$l.'<hr>';     unset($post_title, $row, $post_id, $defaults); } ?>