The best course of action is to investigate the cause of the memory leak, as this approach addresses the root cause of the issue, preventing future occurrences. After identifying and fixing the issue in the code, restarting the cluster ensures that the fixes are applied and any residual issues are cleared. This method balances the need for a quick resolution with the importance of a thorough investigation to prevent recurrence. Option A is not ideal because it does not address the underlying cause of the memory leak. Option C is not recommended as it allows the performance issues to persist, potentially worsening the situation. Option D is ineffective because it does not resolve the root cause of the memory leak, likely leading to the same issues reoccurring.