latch/lock , buffer - questions.

Hi All, 1) When a thread needs a buffer to read in data , does it acquire any latches/locks.How is the allocation done ? 2) What is the difference between locks and latches. 3) If i want to track , the number of times a PARTICULAR user's operations caused his threads to wait for buffers , where to look? onstat -p 's "ovbuff" is across all users , isn't it ? 4) Related to Ques.1 , for every increment in "ovbuff" of onstat -p is there a corresponding increment in "wait" of onstat -u ? TIA Sathish Sadagopan