MySQL Crashing Under Heavy Load

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Continuing to work on how I performance tune web servers.  One thing I found is that under a heavy load of 50 or more simultaneos requests, an ubuntu process called OOM-Killer would kill some of my processes.  Not that big of a deal right?…ubuntu just trying to keep my system up and running?  Wrong…It was killing mysqld.  This being a web server, thats not an ideal situation to have.

I learned that by default on aws ec2, there is no swap file included on t1.micro instances.  A swap file is essentially Virtual Memory.  When the server runs out of real memory, it can write to swap and use this as well.  This was what I needed.  To create a swap file if not exists, simply do the following:

**Note: replace 1024 with the size of swap file you want.  Typically, about twice your allocated real memory.  The first line may take a while since it actually writes an empty 2gb data file to /var/swapfile.  Please also note that ideally, a separate disk or partition would be used for swap, and not just a file on your root, but this works in a pinch.

sudo dd if=/dev/zero of=/var/swapfile bs=1M count=1024
sudo chmod 600 /var/swapfile
sudo mkswap /var/swapfile
echo /var/swapfile none swap defaults 0 0 | sudo tee -a /etc/fstab
sudo swapon -a


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