After install fix pack or APAR, if aix need reboot? if not, do we need stop database and all applications before we install fix pack or APAR?
I've worked on several AIX upgrade rollouts in the past 18 months and they always include a reboot at the end as part of our standard procedure. I'm not sure if it is 100% required, you'd have to study the IBM documentation or ask them to be sure. But it is just too risky not to reboot. If you don't do it immediately and there is a problem next time you reboot it will be far harder to troubleshoot. And it may be too late to roll back the upgrade depending on what else has changed since.
For serious maintenance you should bring the system down to single user mode, or at a minimum stop all user running applications before applying a fixpack. If I was patching/upgrading/fixing an operating system I would not have user databases running.
You might want to read this thread for an explanation about how to determine if a reboot is required or not.
Anyways, i agree with porter and rhfrommn: regardless of if a reboot being required or not, regardless of the application being affected or not it is better not to take any possible risk and bring the applications down first and reboot afterwards.
Two reasons for doing so even if it is not absolutely required: you eliminated one possible source of trouble and successful systems administration is often exactly that: stay clear of dark waters even if you know you could swim if you must.
Second: by setting the rules for doing maintenance work thoroughly you keep the users from becoming "version junkies". If it is no effort at all and can be done without even stopping the application chances are you are asked to apply each and every fix they ever have heard of at the moment they leave the development labs (if not even earlier) - why not? It's only your effort, not theirs. Usually such an upgrade policy is affecting the systems stability adversely.
If it is their effort too, because the machine is unavailable for some time and they have to plan for that you usually are asked to keep the upgrade work to the absolute necessary minimum - which is in most cases a good idea.
bakunin