Re: memory usage estimation.

[James Day]

Try to estimate the working set needed to respond to the queries and get at least that amount of RAM, with the option for more. It's hard unless you know the way the application behaves under real load and even then it isn't easy to make the best balance between RAM and disk when momey is limited. Disks are best if you don't think you can get the working set into RAM, RAM is best if you are confident that you can.

If you have many database servers you have the advantage that you can have some with more RAM than others and you can use live tests to prove your theories. This is how I do it.

On *nix systems, iostat is very helpful. On all systems, show table status to get the average record sizes can be combined with what you know about usage patterns to try to estimate working set size. It's still very difficult.