As described in Wikipedia: tmpfs is intended to appear as a mounted file system, but stored in volatile memory instead of a persistent storage device. Simply put, when you copy a file to such FS, this means that you copy a file to the RAM. When you create a file in this FS, this means you create a file in RAM. When you delete a file in this FS, this means you delete a file in a RAM. And so on.
The negative side of tmpfs is that it's not backed by any storage: on restart or system crash you'll lost your files and data stored in tmpfs. But on system start you can either copy files from the disk to the memory again and continue to work.
In case of IDEA cache, I will need to write a simple script that periodically copies the cache from tmpfs to the disk. So, on restart, I can simply restore cache, and don't need to wait while re-caching is done.
So, how to create a tmpfs storage? It's pretty easy to do with next commands. Here I create an empty directory
tmp and mount it as tmpfs filesystem.# mkdir ~/tmp # mount -t tmpfs -o size=500m tmpfs ~/tmpOption
size=500m limits memory usage to 500m. tmpfs also supports flushing content to the swap when need. This is one of the main differences between tmpfs and ramfs. ramfs is not limited and can grow dynamically, and the used memory can't be freed or flush to swap. The negative side of such dynamic nature of ramfs is that system can hung when no free memory left. To read from and write content to RAM is much much faster than to do the same operations with a file on disk. It's pretty good optimization if you need to support read-only content or content that can easily be restored when need.
Such type of content is a hosted website. You can decrease page or resource loading time by moving them from hard disk to the memory filesystem.
# mkdir /var/www/www.example.com # mount -t tmpfs -o size=50M tmpfs /var/www/www.example.com # cp -R /home/www/www.example.com/* /var/www/www.example/com
To mount tmpfs automatically on system load, you will need to add another record to yours
/etc/fstab configuration file. The only you need to do now is execute next command on system start:# cp -R /home/www/www.example.com/* /var/www/www.example/com
As a summary, tmpfs is a good way to work with large amount of files or data that need to be accessed or processed quickly. Such data also is either read-only or can be easily recreated. Samples of such data are static websites, website resources, temporary cache etc. When need to process large amount of data, you can also split it into small pieces and process each one by one. tmpfs is also takes a limited amount of RAM, and can increase over that amount.
