mem_fragmentation_ratio
<sxh bash>
# redis-cli -h 172.24.16.7 -p 6379 INFO | grep mem
</sxh>
https://redis.io/topics/memory-optimization

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The fragmentation is calculated as the amount of memory currently in use (as the sum of all the allocations performed by Redis) divided by the physical memory actually used (the RSS value). Because the RSS reflects the peak memory, when the (virtually) used memory is low since a lot of keys / values were freed, but the RSS is high, the ratio mem_used / RSS will be very high