How to improve the performance when using a flat-file dataset and PHP for implementing advanced search function?

Query Monitor is a good way to track what part of WP is chewing up resources. What search functionality are you trying to implement, exactly? It’s very hard to give advice based on a vague question that leaves out relevant details.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)