Between allocator_frag_ratio and mem_fragmentation_ratio, which one should I monitor in Redis?

Question

Between allocator_frag_ratio and mem_fragmentation_ratio, which one should I monitor in Redis?

1. What is differences between them?

2. For monitoring redis cluster state, What properties should I monitor additonally?

3. In zabbix redis template, errors occur when mem_fragmentation_ratio > 1.5. when redis is installed and keys don't exist, in my case, mem_fragmentation_ratio > 1.5. is it meaningful alarm? If not, Can I mute these event alarm?