database - DBS-2 phase locking -


does know, why these transactions t1 , t2 don't folow two-locking phase ? (it said because unlock(y) followed write_lock(x) in transaction t1 , same in t2 , why doesn't follow 2 phase locking, don't understand, explain me? )

thank you

t1

read_lock(y ); read_item(y ); unlock(y ); write_lock(x ); read_item(x ); x := x + y; write_item(x ); unlock(x );`

t2

read_lock(x ); read_item(x ); unlock(x ); write_lock(y ); read_item(y ); y := x + y; write_item(y ); unlock(y );


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