A collection of tips and tricks, which (might) improve the stability of your peer.
Reduce the Workload
In the performance settings (http://localhost:8090/Performance_p.html) under "Use Default Profile" choose a value lower than 100%. This will proportionally adjust the settings under "Scheduled tasks overview and waiting time settings" (http://localhost:8090/PerformanceQueues_p.html). DON'T change these settings manually, unless you know what you are doing!
Extra RAM for the OS (Linux)
Making sure that the operating system has more than enough RAM to operate can greatly improve the stability of your peer. Under Linux, 1-2GB of unallocated RAM for the OS can have a very pleasant effect to yacy. That has been reported from at least one yacy user. (Linux automatically uses free RAM as cache for frequently used files. That might be the reason for the stability improvement.)