Reduce string allocations and retentions

[casperisfine]

While running memory_profiler agaisnt our app, I noticed quite a lot of duplicated strings coming from whois:

Retained String Report
-----------------------------------

1059  "whois.arin.net"
1059  /tmp/bundle/ruby/2.5.0/bundler/gems/json-b5f423ccf08f/lib/json/common.rb:155


689  "whois.lacnic.net"
689  /tmp/bundle/ruby/2.5.0/bundler/gems/json-b5f423ccf08f/lib/json/common.rb:155


387  "whois.donuts.co"
196  /tmp/bundle/ruby/2.5.0/gems/psych-3.1.0/lib/psych.rb:456
191  /tmp/bundle/ruby/2.5.0/bundler/gems/json-b5f423ccf08f/lib/json/common.rb:155


314  "whois.ripe.net"
314  /tmp/bundle/ruby/2.5.0/bundler/gems/json-b5f423ccf08f/lib/json/common.rb:155

So here's I'm trying to reduce these duplications as to reclaim a bit of memory. The whole thing rely on String#-@ which starting in MRI 2.5 will freeze and possibly intern the string.

On 2.4 and older (or some oldish alternative implementation) it will fallback to simply freezing the string, so no memory will be saved, but for the caller the string will still be frozen so that should prevent any kind of weirdness when upgrade the ruby version.

[weppos]

Thanks @casperisfine , this looks great. Are you able to share some insights about the allocation improvement?

[casperisfine]

@weppos I'd need to re-run the profile with this gem patched. It would take ~20m. However I'm confident all these duplications will disappear as I already did some very similar PR on several gems.

But tell me and I can trigger a profile.

[casperisfine]

Ok, so I just ran the profile anyway.

These strings are effectively gone from the retained string reports as expected.

As for the overall impact, the total retained memory difference is that this branch retain 490kiB more memory while we expected the inverse.

That being said the baseline was using whois-3.6.5, so that's likely why. I'll trigger another profile against 7f67e4e

[casperisfine]

Ok, so compared to 7f67e4e:

Retained memory: -350kB
Retained objects -2378

So I'd say it's a decent saving.

[casperisfine]

Are you able to share some insights about the allocation improvement?

Oh, I just figured you were asking about allocations vs retention. I totally forgot to explain to allocation part:

On master:

Allocated String Report
-----------------------------------
8628  "host"
4159  /tmp/bundle/ruby/2.5.0/bundler/gems/whois-7f67e4e6e8ea/lib/whois/server.rb:78
3845  /tmp/bundle/ruby/2.5.0/bundler/gems/json-b5f423ccf08f/lib/json/common.rb:155

That is why I added the magic comment on the top of the file, this way it saves 4k allocations of "host".

Looking at the overall allocation savings I see a 830MB and 93084 objects saving, but that seam way too good to be true, memory_profiler must be confused by something.

[casperisfine]

but that seam way too good to be true

Ok, yeah the difference come from on having some cache loaded, while the other was fresh, so simply ignore that.

The actual allocation reduction should be is

before: 1.63 MB whois-7f67e4e6e8ea

after: 1.09 MB whois-879f6e7c1ef3

So a bit over 500KB saved.

[weppos]

Sweet, thanks! ❤️

[weppos]

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