Getting "Unable to contact search service" periodically

Dear All,

We are running Openfire 3.7.1 on CentOS 6.2 x86_64 using Java 1.7 and MySQL 5.1.61. We have around 3,000 users across different regions with around 200 - 300 active sessions at any given point in time. The server has 4GB of RAM with 512MB of Heap Memory configured. We do not get Out-Of-Memory errors and reboot the server automatically every Sunday early morning to avoid memory leak issues.

We’ve configured Active Directory (i.e. all these 3,000 users come from AD) and we are experiencing “Unable to contact search service” error messages while trying to use Spark’s search functionality at times. When this happens a server reboot fixes the problem. This is how it looks:

http://screencast.com/t/FrWiRaO3

I’ve spent some time looking through server logs but I’ve been unable to find anything suspicious/meaningful to date.

Could someone point out a specific log file or way of understanding what is causing this issue?

Thank you so much