Linux and *BSD Support

[burke]

This PR migrates from xattr as a cache backend to a simple directory of files.

The cache file naming scheme is A/B[0..1]/B[2..-1], where:

• A is the cache_dir provided on Bootsnap.setup;
• B is a hex-encoded FNV1a-64 hash of the fully-expanded path of the file being cached.

The cache key is similar to the previous iteration with the following significant changes:

• Added original file size to cache key (size) as added insurance against hash collisions, etc. Probably not necessary, but it's effectively free.
• Padded cache key to 64 bytes in order to be able to change it in the future without modifying its length.

As a bonus, this seems to be (very) marginally faster than master.

---

This unfortunately ends up being a fairly brutal diff to review since it's a near-complete rewrite of bootsnap.c, so if I've tagged you for review, I won't hold it against you if you only take a cursory look. I think the C got a little bit easier to read than it was before but it's still a bit of a project.

/cc @SamSaffron

[burke]

¯\_(ツ)_/¯ I'm just gonna merge and encourage people to try out 0.3.0.pre.

[SamSaffron]

totally fine with me, I am meaning to do some perf measurments on boot impact, will let you know once it is done.

[SamSaffron]

This is looking awesome performance wise @burke

Baseline on Linux:

sam@ubuntu discourse % time bin/rails r 'I18n.t "test"'
bin/rails r 'I18n.t "test"'  3.06s user 0.73s system 98% cpu 3.857 total
sam@ubuntu discourse % time bin/rails r 'I18n.t "test"'
bin/rails r 'I18n.t "test"'  3.07s user 0.72s system 98% cpu 3.862 total

0.2.14 on Linux:

bin/rails r 'I18n.t "test"'  2.81s user 0.29s system 98% cpu 3.140 total
sam@ubuntu discourse % time bin/rails r 'I18n.t "test"'
bin/rails r 'I18n.t "test"'  2.77s user 0.27s system 98% cpu 3.074 total
sam@ubuntu discourse % time bin/rails r 'I18n.t "test"'
bin/rails r 'I18n.t "test"'  2.85s user 0.30s system 98% cpu 3.185 total

0.3.0.pre no ISEQ/YAML cache yet:

sam@ubuntu discourse % time bin/rails r 'I18n.t "test"'
bin/rails r 'I18n.t "test"'  2.52s user 0.35s system 98% cpu 2.900 total
sam@ubuntu discourse % time bin/rails r 'I18n.t "test"'
bin/rails r 'I18n.t "test"'  2.54s user 0.33s system 98% cpu 2.914 total
sam@ubuntu discourse % time bin/rails r 'I18n.t "test"'
bin/rails r 'I18n.t "test"'  2.57s user 0.34s system 98% cpu 2.950 total

0.3.0.pre ISEQ cache

sam@ubuntu discourse % time bin/rails r 'I18n.t "test"'
bin/rails r 'I18n.t "test"'  1.88s user 0.59s system 97% cpu 2.519 total
sam@ubuntu discourse % time bin/rails r 'I18n.t "test"'
bin/rails r 'I18n.t "test"'  1.77s user 0.60s system 97% cpu 2.416 total

0.3.0.pre ISEQ + YAML cache

sam@ubuntu discourse % time bin/rails r 'I18n.t "test"'
bin/rails r 'I18n.t "test"'  1.62s user 0.63s system 97% cpu 2.297 total

Excellent work. This is faster than old version under ALL conditions for us.

[zmoazeni]

Works here too on ubuntu 16.04.

Cuts off about 2.5 seconds from the bootup on our codebase. Thanks for the hard work!!

[SamSaffron]

@zmoazeni what was the absolute time prior to bootsnap?

[zmoazeni]

@SamSaffron re-running the same command you posted above here's before and after:

# without bootsnap
∴ time bin/rails r 'I18n.t "test"'

real	0m4.188s
user	0m3.068s
sys	0m1.036s

# 0.3.0.pre ISEQ + YAML cache
∴ time bin/rails r 'I18n.t "test"'

real	0m1.820s
user	0m1.660s
sys	0m0.140s

[SamSaffron]

wow... that is huge!

[zmoazeni]

Here's another data point. The numbers above were from my beefy development machine.

Here's the numbers on the same codebase on a Dell XPS 13 also running Ubuntu 16.04 (my travel machine):

# without bootsnap
∴ time bin/rails r 'I18n.t "test"'

real	0m7.020s
user	0m4.744s
sys	0m2.196s

# 0.3.0.pre ISEQ + YAML cache
∴ time bin/rails r 'I18n.t "test"'

real	0m2.507s
user	0m2.244s
sys	0m0.232s