The NodeInstanceLog table will give the entries about a processInstance regarding the nodes that were entered and exited. If, in the process, there is a Human Task node and during the execution of the process the flow reaches at the human task node, an entry is creates in NodeInstanceLog table, task is created etc, then some user acts upon it and completes the task, again another entry is created in the NodeInstanceLog showing the exit information of the node.
Looking from the NodeInstanceLog for human tasks how to find out who has acted upon the task. This information is present in the Task table but there is no relationship between this table and NodeInstanceLog.