Some doubts about streaming startpoint in WaitForWALToBecomeAvailable()

[蔡梦娟(玊于)]

Hi, all
I have some doubts about the request xlog streaming startpoint in 
WaitForWALToBecomeAvailable(). In this function, RecPtr is the endpoint lsn we 
are waiting for, tliRecPtr is the position of the WAL record we are interested 
in, I want to know why use RecPtr rather than tliRecPtr as the startpoint when 
call RequestXLogStreaming, although the start position will be set as the 
beginning of the corresponding segment in RequestXLogStreaming.

Thanks & Best Regard