1 INTRODUCTION  
2 BACKGROUND  
3 SURVEY METHODOLOGY  
4 ANSWERING RQ1: WHAT ARE THE QUERY-END OPTIMIZATION METHODS IN CODE SEARCH STUDIES?  
5 ANSWERING RQ2: WHAT ARE THE CODE-END OPTIMIZATION METHODS IN CODE SEARCH STUDIES?  
6 ANSWERING RQ3: WHAT ARE THE MATCH-END OPTIMIZATION METHODS IN CODE SEARCH STUDIES?  
7 CHALLENGES AND OPPORTUNITIES FOR FUTURE WORK  
8 THREATS TO VALIDITY  
9 CONCLUSION