In general only 1 gig of RAM is pretty light for as large an installation as you have. If you're only using but half of that gig you're not doing your server or it's discs a favor.

All of that extra unused RAM could and should be used for database caching. More memory cache less disc access.

As for why your machine becomes unresponsive we likely cannot tell you unless we're there to see it, but experience can be helpful. Here's the most common scenario that I've seen -

Machine is either low on resources or isn't using them well but hums along just fine until something is done that brings it close to the edge of it's limits. Maybe it's a bunch of searches all at the same time, maybe it's a huge cache rebuild that occurs while a search is being run. Whatever the exact cause, it was a combination of things that brought a machine close to it's max out put.

Now the machine is slowed and requests start to back up. Perhaps it's disc IO that is the culprit. Memory use while the machine is backing up still looks fine. Load, while rising isn't huge. That's because the discs are so backed up nothing is being processed. Load is climbing though because of the number of processes that are waiting for disc.

Doesn't take but a few seconds in that state to get a locked up server. Nothing is going to fix it now except a reboot.

Do I know if that is what happened to your machine? No. But I wouldn't be surprised at all. I see it every day. You've got a gig of RAM, which is light for your volume, and only half of that is in use. Just think how much better the thing would run if it was making efficient use of the entire gig of RAM?

Go here and read the tuning tutorials. A gig likely isn't enough for your traffic by why have a gig of RAM if you're only using half? Get that machine making more efficient use of your RAM and it will help.

Of course, I'm taking your word that it is only using half the gig. That in itself sounds kinda fishy to me. Do yourself a favor and verify that again before you make any changes to your MySQL.

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