系统是如何确定PRIMARY CF和SECOND CF？

看了以前的老笔记 “db2instance -list\"

ID TYPE STATE HOME_HOST CURRENT_HOST

-- ---- ----- --------- ------------      

0 MEMBER STARTED s1 s1 NO 0 0 s1

1 MEMBER STARTED s2 s2 NO 0 0 s2

128 CF PRIMARY s0 s0 NO - 0 s0

129 CF CATCHUP s3 s3 NO - 0 s3