Divide a cache into pools based on the proportion of the I/O performed by your queries that use the corresponding I/O sizes. If most of your queries can benefit from 16K I/O, and you configure a very small 16K cache, you may see worse performance.
Most of the space in the 2K pool remains unused, and the 16K pool experiences high turnover. The cache hit ratio is significantly reduced.
The problem is most severe with nested-loop join queries that have to repeatedly reread the inner table from disk.
Making a good choice about pool sizes requires:
Knowledge of the application mix and the I/O size your queries can use
Careful study and tuning, using monitoring tools to check cache utilization, cache hit rates, and disk I/O
