Weird issue - any ideas?
 

Stating about this time yesterday, vBulletin (4.2) started reporting 3,600+ guests online and server loads of 90+. At first I though it was just a traffic spike, but it didn't go down at all, even overnight. It's still saying 3,600+ guests right now. And, of course, lots of slowdown and timeouts.

The really weird part is that Google Analytics is not seeing these guests. According to Google, traffic is completely normal.

I've tried rebooting the server, but anything more is pretty much beyond me.

Does anybody have any idea what might be happening?

Are your cronjobs in the admin control panel correctly configured?
Try clearing the `session` table in the database.

I don't have solution for this, bud I had same issue before 5 months. it made me crazy, I tried many things with out finding something to change fake traffic.

Finally I closed forum for 5 hours, after that and 3 days that I had this traffic it started to keeping get down traffic every hour and at the end of the day traffic went to normal for my forum.

I don't know if the solution whas that I closed for some hours or coincidence.

What is your cookie/cache time set at in the admincp? Is that what you are going by?

It's finally started to calm down - now only showing 500 visitors, not 4000. No change in Google Analytics still.

900 seconds (I think that's the default 15 mins?) I'm not sure how that helps, though - whatever it's set to, it's a 12-fold increase in traffic.

It is just search bots most likely. What are the ip's?

What, a sudden simultaneous influx of 4000 searchbots? Is that likely?

I couldn't check the IPs because the site was pretty much inaccessible at the time, and they were guests, anyway, not accounts. Is there a way to check the IPs of guests?

Yes, it happens.

You can check your server logs to find the ips, etc.

The session table in the database also contains information about all active visitors/members.

That it does, in detail as well I love it. Use this table while those you suspect bots or humans are on, you can view all sorts of handy data which is why Dave mentioned it!

If you do happen to get hammered though... if session table has over 30,000 entries that is when you will start to experience issues and that would mean its not bots but you're site is being targeted. You can truncate the table using sql query and alleviate the stress on the site but all those who were logged on or navigating will no longer be doing what they were prior i.e. after you truncate the session table its basically like kicking everyone out humeans/bots/members/non-members with a huge boot! DO NOT do this if only 4k visitors that does not seem hacker/mal bot related.