Runtime Metrics: Global VM cache statistics #1680
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| sig { params(ground: Symbol, num: Integer).returns(Indexed) } | ||
| sig { params(ground: Symbol, num: Integer).void } |
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This is my first time making changes because of sorbet. Is this the right thing to do here? @ivoanjo?
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I'm... not entirely sure. Did you do this change manually, or was it a result of a sorbet autofix? Since this is provided by sorbet, I don't think we're supposed to maintain it manually... 🤔
I took a slightly different approach an in #1679 I just re-ran bundle exec srb init and sorbet marked this file as typed: ignore. (It seems like it's since been fixed upstream sorbet/sorbet-typed#372).
In that PR, I also pinned the Sorbet version so we don't run into these random "oh sorbet updated and now it doesn't like its own rbi" issues again, since this was the second time we got bitten.
So my suggestion would be to just rebase on top of that PR (or master, once merged) instead :)
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Also for reference, https://twitter.com/tenderlove/status/1433479390583611392?s=20 is a great thread about this as well :) |
| module Environment | ||
| # Reports Ruby VM cache performance statistics. | ||
| # This currently encompasses cache invalidation counters and is CRuby-specific. | ||
| # | ||
| # JRuby emulates some CRuby global cache statistics, but they are synthetic and don't | ||
| # provide actionable performance information in the same way CRuby does. | ||
| # @see https://github.com/jruby/jruby/issues/4384#issuecomment-267069314 | ||
| # | ||
| # TruffleRuby does not have a global runtime cache invalidation cache. | ||
| # @see http://archive.today/2021.09.10-205702/https://medium.com/graalvm/precise-method-and-constant-invalidation-in-truffleruby-4dd56c6bac1a | ||
| module VMCache | ||
| module_function | ||
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| # Global constant cache "generation" counter. | ||
| # | ||
| # Whenever a constant creation busts the global constant cache | ||
| # this value is incremented. This has a measurable performance impact | ||
| # and thus show be avoided after application warm up. | ||
| def global_constant_state | ||
| ::RubyVM.stat[:global_constant_state] | ||
| end | ||
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| # Global method cache "generation" counter. | ||
| # | ||
| # Whenever a method creation busts the global method cache | ||
| # this value is incremented. This has a measurable performance impact | ||
| # and thus show be avoided after application warm up. | ||
| # | ||
| # Since Ruby 3.0, the method class is kept on a per-class basis, | ||
| # largely mitigating global method cache busting. `global_method_state` | ||
| # is thus not available since Ruby 3.0. | ||
| # @see https://bugs.ruby-lang.org/issues/16614 | ||
| def global_method_state | ||
| ::RubyVM.stat[:global_method_state] | ||
| end |
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Great docs/research! I'm curious on the omission of class_serial, did you look into it and find it less useful?
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class_serial doesn't have a directly measurable negative performance impact on the application: it's a value that normally keeps going up on new class creation. But small class creation is a normal part of any sufficiently complex framework.
Because the fact of creating a class is in itself not harmful, I wasn't able to find a strong argument to report it, as I believe it won't be actionable. The other two method caches statistics in the PR captures any case where dynamic class/method modifications actually cause concerning issues.
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But small class creation is a normal part of any sufficiently complex framework.
During request handling? I would've thought that it would "flatten out" at some point.
Happy to go with your decision; we can always revisit it if there's customer interest for that value.
Codecov Report
@@ Coverage Diff @@
## master #1680 +/- ##
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Coverage 98.31% 98.31%
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Files 925 927 +2
Lines 44564 44617 +53
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+ Hits 43812 43865 +53
Misses 752 752
Continue to review full report at Codecov.
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Add
global_constant_stateandglobal_method_statetoddtraceruntime metrics.These values track how many times the global Ruby VM cache had to be rebuilt, due to changes in constant declaration or method declarations. Both values are monotonically incrementing integers.
Such changes have a large performance impact, so it's important to ensure that these values rarely change after a product application has finished warming up.
More information about method caching here: https://tenderlovemaking.com/2015/12/23/inline-caching-in-mri.html
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