Database going down frequently

My database is going down frequently these days…by the time of this posting my database has gone down the 41th time. I cannot find the reasons it goes down daily, but this is what my apache error logs show.

[Sat Jul 04 08:32:45 2009] [error] [client 75.127.106.65] client sent HTTP/1.1 request without hostname (see RFC2616 section 14.23): /w00tw00t.at.ISC.SANS.DFind:)
[Sat Jul 04 19:32:20 2009] [error] [client 216.168.43.234] client sent HTTP/1.1 request without hostname (see RFC2616 section 14.23): /w00tw00t.at.ISC.SANS.DFind:)
[Sun Jul 05 02:27:19 2009] [error] [client 78.40.248.119] Invalid URI in request _csuid=4a4eb49d5ce1e79b
[Sun Jul 05 02:27:22 2009] [error] [client 78.40.248.119] Invalid URI in request -Alive: 300

Is there anybody who knows what these error logs means? I would be very thankful if anyone can reply ASAP.