The ratio is the ratio of serialised bytes for a memtable to actual JVM allocated memory. Using a ratio below 1 would imply the JVM is using less bytes to store the memtable in memory than it takes to store it on disk (without compression). 

The ceiling for the ratio is 64. 

The ratio is calculated periodically so if the workload changes, such as system start up, the number will lag behind. I would guess numbers less than 1 mean the memtable does not have any data. 

Cheers

-----------------
Aaron Morton
Freelance Developer
@aaronmorton

On 1/02/2012, at 8:27 AM, Radim Kolar wrote:


 but a ration of<  1 may occur
for column families with  a very high update to insert ratio.
better to ask why minimum ratio is 1.0. What harm can be done with using < 1.0 ratio?