Comment 3 for bug 1425528

I'm not sure why dataset-size option is even there - one should configure innodb_buffer_pool_size based on the amout of RAM the machine has - the datasize is pretty irrelevant. If the dataset is smaller than the configured innodb_buffer_pool, then mysql will not use 'extra' configured memory. If it is larger (which is not uncommon on large datasets) only portion of the dataset will fit inside buffer pool.

Ideally you'd want to set innodb_buffer_pool_size cca 10-15% larger than your dataset. But, as explained above, there is no harm making it larger than the dataset.

The limiting factor is the amount of RAM, not the dataset size. That is why I'm suggesting to completely remove that option from the charm, as it is misleading.

What a operator should take into consideration is are there going to be other services deployed on the unit where mysql is runnig? If yes, then mysql should be given less memory.

I'd say sane default should be 50% of available RAM - although a operator should be aware of the option and tune it.