Is there any way that I can reload /etc/my.cnf without restart mysqld:
# mysqladmin -u root -p shutdown
# mysqld_safe &

I mean can I reload my.cnf in mysql client
mysql>
?

Or is there any other tools. I haven't found such command of mysqldadmin to do this.

Because the database is busy and there is always some programs insert datas to it.

Thanks.

It's probably a bad idea to reconfigure the sql daemon while the database is busy. All the same you could try this at the bash command line, not in the sql command prompt.

kill -HUP <pid>

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You can, as far as reloading from the "mysql>" prompt, use the "system" command, as in:

system su -c '/etc/rc5.d/S20mysql restart'

A better solution, especially for a heavily used system, is to reexamine your configuration, and make improvements. One thing I'd suggest is making sure you have a second server, and set them up for replication. This will allow you to take one machine "offline" for a while, make your changes, then sync with the second server when you're finished. Using virtual machines (such as Xen), you don't even need to add hardware, if that's an issue.

This has numerous benefits. For one thing, you'll have a backup system, if needed. Second, you'll be able to perform backups more efficiently, without losing data or missing transactions, while retaining good end user speeds. Third, especially in your current situation, if there is a problem when you go to restart, you don't end up completely out of luck, having to scramble to undo your changes. Finally, it offers you a second system to test new ideas and software, without major downtime and related headaches.

If your information is that heavily used and important, it's something I'd seriously look into. More info on mysql replication is here:

http://www.onlamp.com/pub/a/onlamp/2.../MySQLian.html

and Xen info is here:

http://www.cl.cam.ac.uk/Research/SRG/netos/xen/

Hope it helps!

Actually he should be fine as the kill -HUP is designed to allow existing threads to complete before the process is killed.

I'm glad to hear that my suggestion was better than I had thought. I knew it was good for various daemon processes but the database server process was a concern to me.