In my opinion, server downtime is not tolerable. So, rebooting is not an answer especially in Enterprise level infrastructure. So, what i will do in this case is do a root-cause-analysis. Why is it slow ?
Things to look at.
1. Verify server hardware working fine.
2. Run your system "uptime" command to identify your system load against your number CPU.
3. Run the "sar" utility and capture where is it having the bottle neck:
--> CPU
--> Disk I/O
--> Memory
--> Run queue length
4. Lastly, when it is not your server and OS problem. Time to ask the DBA to review your SQL and application coding. Poor coding can result in un-optimized system performance.
5. Lastly running an app server and db server at the same server is not recommened if cost is a concern.