# ffcnt
Fast file counting for spinning rust, in rust.
ffcnt's sole purpose is to provide a faster alternative to `find /some/path/ -type f | wc -l`.
It achieves that by looking up the extent map *of directories* and reordering recursion into the directory tree by the physical offset of the first extent of each directory.
This greatly reduces disk seeks.
## Requirements
* Linux
* A filesystem that supports the `fiemap` ioctl on directories.<br>
Currently **ext4** is known to provide that. If you know other ones, please report!<br>
Incompatible filesystems will work but gain no speedup over `find`.
You can test filesystem support with the `filefrag` tool.
```
## supported
$ filefrag /tmp/
/tmp/: 3 extents found
## unsupported
$ filefrag /mnt/test/
/mnt/test/: FIBMAP unsupported
```
## Binary
You can find prebuilt x86_64-linux-glibc binaries without debug information under [releases](../../releases).
For troubleshooting and other environments you'll have to build your own.
## Build
* clone repo
* install rust nightly and cargo
* `cargo build --release`
## Unscientific Benchmark
Idle system:
```
# echo 3 > /proc/sys/vm/drop_caches ; time ffcnt .
196608
real 0m23.889s
user 0m1.233s
sys 0m2.127s
# echo 3 > /proc/sys/vm/drop_caches ; time find . -type f | wc -l
196608
real 2m31.562s
user 0m0.557s
sys 0m3.860s
```
Busy system with mixed read/write workload. Differences in file counts arose due to writes happening in the meantime:
```
# echo 3 > /proc/sys/vm/drop_caches ; time ffcnt .
4411262
real 10m36.288s
user 0m3.656s
sys 0m7.588s
# echo 3 > /proc/sys/vm/drop_caches ; time find . -type f | wc -l
4412101
real 45m54.955s
user 0m3.212s
sys 0m12.044s
```
Both tests were performed on HDDs and the files were spread over 65536 directories with a nesting depth of 2, i.e. a branching factor of 256.
## Ideas
* 1 thread per block device in tree
* filter by name
* optimized du