you are giving the answer ...WP is a heavy user of memory by it's numerous MySql requests.
How many uniques on that site ?

About 15,000/day

you still shouldnt be having issues UNIX can tell you what the problem is. as someone noted you could run top or memstat or netstat or several others that would tell you why its dying

till then you are simply shotgunning the problem.

well, that is much less then my client :


VISITS:
Average Per Day 89,772
Average Visit Length 0:29
Last Hour 4,270
Today 4,438
This Week 628,404

PAGE VIEWS

Average Per Day 118,646
Average Per Visit 1.3
Last Hour 5,626
Today 5,862
This Week 830,521


If your box is a colo, add the memory... If a rented box, well maybe check the top command to see ( that is hat I ran a few post avbove ).

Ok, sounds good. Pageviews is actually pretty much the same as for your client. Will check the top command and then decide. Thanks.

Removed the plugin, running fine since 2 hours now.

Yes, it looks like it was the UserOnline plugin. Site is running since 12 houus without a problem after I removed it.

sandman!, what would be reasonable for an additional Giga? My hosting company gave me this which sounds pretty steep to me:

- 1GB RAM: Eur 19,00/month.
- Install fee: Eur 99,00.

that is a lot... find a new host... paying per month on ram is stupid.

I can't praise the guys from Webair enough, they are just great. Remember, I'm not even a Webair customer (yet!) but they had one of their tech guys take a look at my server and I got some very helpful input from it. And then they put me together with another of their stuff who is a Wordpress expert and who took almost 2 hours of his time to help me.
Without being one of their customers Webair gave me better service than any hosting company that I've ever been a customer of! :thumbsup

Plugins will kill you.

50 dead plugins