get & p-lock page
lock row
p-lock & latch page
test to see if existed most current copy of page, if yes then refresh page
update page
release latch
commit
write changed page
release row lock
write changed page into GBP可以發生在commit之前(到了一個check point)，但是必須在release latch之後，此時該條record仍然是收保護的，因爲上面有row lock,直到commit(commit會把GBP裏的內容回寫到DASD上）過後纔會釋放。