Phase V: Job execution. In this phase, the G-Hadoop system executes the jobs that the user has submitted. The execution of the job is similar to G-Hadoop without the designed security framework. One difference is that the master node must assign a task to a slave node with the user session U_Session as an authentication information, and correspondingly, the slave node checks the user session for expiration time before executing tasks. If the user session is expired, the slave node asks the master node to update the life cycle of the user session. In this case, the master node simply applies a new proxy credential and sends it directly to the slave node. By receiving the new proxy credential, the slave node updates the expiration time of the user session as well as the proxy credential.