Mysql Update Speeds

[Paul]

Hello,

I know mysql update queries can only utilize one index, making them
slow in some cases.

My update are taking about 3 hours, joining 2 tables on their primary
keys. (table sizes about 1 mil in 1 table, 2 mill in the other).

My real question though is, mysql is only using about 10% of the cpu
whilst running this update query (on a linux server), what can I do to
let it run flat out at 100%, and presumably finish 10 times quicker?

Or isnt it as simple as that, is hard drive access the bottle-neck?
Select queries always seem to run a lot quicker and use a lot more of
the cpu.

Many thanks,

Paul

[Aggro]

Paul wrote:

Or isnt it as simple as that, is hard drive access the bottle-neck?
Select queries always seem to run a lot quicker and use a lot more of
the cpu.

When you update, you will use the hard drive propably a lot of times(for
writing), but also for reading (to search correct rows).

When you run a select, you propably use some indexes, which means less
reading and more comparing (more cpu usage).

Also writing is usually always slower than reading, so I think it really
is that simple. Your hard drive is the bottle-neck.