Performance on query database with Codeigniter -

i'm looking in method best performance on getting data database query, main problem doing next example of query give me error message: preg_match(): compilation failed: regular expression large @ offset 44123 can resolved adding pcre library backtracking limit options php,ini.

it resolve issue on server/hosting not in others if used many users.

my query quite simple:

i have array of 5k of rows:

$data = array(   array('product_id' => 1),   array('product_id' => 2),   ++ 4998 ); 

i need foreach product id , ask database , insert data if exist if not return me product_id doesn't exist, store in array.

//controller method     function test(){         foreach($data $row){             $exist[] = $this->model->askdatabase($row->product_id);         }          if($exist){             $getexistents = $exist;         }          if(!$getexistents == null){              //and here error produced "regular expression large"             $this->db->select('*')->from('products_2')->where_in('product_id', $getexistents)-get();         }     }      //model method     function askdatabase($product_id){         $exist = $this->db->select('id')->from('products')->where('product_id', $row->product_id)-get();          if($exist->num_rows() > 0 ){           return $exist->row()->id;         }else{           return false;         }     } 

is better execute foreach loop again 'where' condition instead where_in ? or there method can better performance on executing query?

any appreciated !