Chapter 18, Problem 19E

Explanation of Solution

Forest protocol not ensuring serializability

• Consider a system with two trees.
• The first tree consists of n1 as the parent node and n3, n4 as the child node of n1. n7 is the child node of n3 and n8, n9 are the child nodes of n4.
• The second tree consists of n2 as the parent node and n5, n6 as the child node of n2. n10 is the child node of n5 and n11, n12 as the child node of n6.
• There are two transactions T₁ and T₂.
• The legal schedule include:

T₁                T₂

        lock(n1)

        lock(n3)

        write(n3)

        unlock(n3)

                        lock(n2)

                        lock(n5)

       ...