Storing PHP Sessions/File Caches in Memory using TMPFS
Yesterday I was looking through some application logs and noticed a significant bottleneck with I/O reads in the implemented file cache. This cache is used to temporarily store processed views and records for a set duration. I looked into a couple of solutions to alleviate the intense spinning disk usage, ranging from Memcache to Redis. These products are great for large-scale applications spread over multiple systems. However, in my case, a single local configuration was sufficient.
This was when I found ’tmpfs’, saving me from all sorts of issues relating to adding yet another application to the production stack. ’tmpfs’ appears as a mounted partition on your system. Under the hood, it allocates and uses a section of physical memory (non-persistent through reboots). This means that you are able to configure directories, such as the cache, to be mounted on a ’tmpfs’ partition. This results in the desired speed boosts without tampering with the application logic itself. Even better, if the mount is unsuccessful for some reason, it will safely fall back to using the persistent hard-disk solution.
PHP Sessions
Though I have been discussing this solution in the case of caches, file-based PHP sessions can be set up in a similar manner. You must first work out where session files for your PHP installation are stored. Note that if you’re using PHP-FPM, you may need to modify the second configuration line.
# /etc/php.ini
session.save_path = /var/lib/php/session
# /etc/php-fpm.conf
php_value[session.save_path] = /var/lib/php/session
We can then make sure that the directory has been created along with the fallback permissions. To temporarily observe performance improvements, we are able to mount the ’tmpfs’ partition to the session directory, setting ownership to the desired user.
mkdir -p /var/lib/php/session
# fallback
chown nginx:nginx /var/lib/php/session
chmod 755 /var/lib/php/session
# temporary mount
mount -t tmpfs -o size=32m,mode=0755,uid=$(id -u nginx),gid=$(id -g nginx) tmpfs /var/lib/php/session
umount /var/lib/php/session
If you are satisfied with the configuration, you can persist the partition mount across reboots by adding the following line to your ‘fstab’ file.
echo "tmpfs /var/lib/php/session tmpfs size=32m,uid=$(id -u nginx),gid=$(id -g nginx),mode=0755 0 0" >> /etc/fstab