Data cache and Result set cache & hit rate %

[Cognos8]

Below are the Default values set in env against cube .Total RAM size is 24 GB. To improve the performance of single cube , shall i increase  data and result cache to 3 GB each?

Data cache size (MB) = 1024
Maximum amount of disk space to use for result set cache ( MB) = 1024
Maximum space for in-memory aggregates (MB) = 1024

In metrics all below values are showing 0%. Atleast Data cache and result set cache hit rate should show some %, why it is not listed

Data cache hit rate = 0%
Result set cache hit rate = 0%
In-memory aggregate cache hit rate = 0%