The InnoDB buffer pool should ideally be divided such that each instance is roughly 1 GiB in size. Given that the buffer pool size is 12 GiB, increasing the number of buffer pool instances to 16 ensures that each instance would be 0.75 GiB, which is closer to the recommended 1 GiB per pool than the currently configured 8 (each being 1.5 GiB). Increasing the number of instances to 32 would make each instance too small (0.375 GiB), and decreasing them would make each instance too large.