Step one is building an index of the file system. This is simply done by walking the filesystem. The resulting index is stored in RAM and a file. On the next app start the index ia loaded from that file, which is much quicker than walking the file system.

Step two is using this in RAM index for searching. This scales really well with the number or CPU cores and on modern systems a normal case insensitive substring search should finish almost instantly with few million files.

The next release will support file system monitoring with inotify and fanotify to keep the index updated. Although this has some drawbacks.