perf(sampling): optimize matching and limit cache memory [APMSP-2948]#1977
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About This ReportThis report tracks Clippy allow annotations for specific rules, showing how they've changed in this PR. Decreasing the number of these annotations generally improves code quality. |
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| let mut cache = self.cache.lock_or_panic(); | ||
| if let Some(&result) = cache.get(subject) { | ||
| return result; | ||
| } | ||
| let result = glob_match_bytes::<true>(pattern, subject); |
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For wildcard rules with cache misses, cache is still locked while glob_match_bytes runs. In concurrent sampling, one high-cardinality or adversarial subject can make every other thread using the same cloned GlobMatcher wait behind the full backtracking match, including threads that would only need a cache hit. The previous implementation released the mutex before doing the match and only re-locked to insert, so this can serialize rule matching under load; consider dropping the guard before computing and re-locking for put.
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🎉 All green!❄️ No new flaky tests detected 🎯 Code Coverage (details) 🔗 Commit SHA: 894e089 | Docs | Datadog PR Page | Give us feedback! |
Codecov Report❌ Patch coverage is Additional details and impacted files@@ Coverage Diff @@
## main #1977 +/- ##
==========================================
+ Coverage 72.64% 72.69% +0.05%
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Files 451 452 +1
Lines 74687 74888 +201
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+ Hits 54253 54443 +190
- Misses 20434 20445 +11
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Artifact Size Benchmark Reportaarch64-alpine-linux-musl
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| // A concurrent inserter racing us on the same key is harmless: `put` overwrites with | ||
| // the same boolean result. |
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But N concurrent inserters would call glob_match_bytes if there is a cache miss.
I guess that's the price we have to pay.
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If we really need to worry about that in the future, there are some concurrent implementations of LRU caches (https://crates.io/crates/concurrent_lru for one)
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yannham
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| // A concurrent inserter racing us on the same key is harmless: `put` overwrites with | ||
| // the same boolean result. |
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If we really need to worry about that in the future, there are some concurrent implementations of LRU caches (https://crates.io/crates/concurrent_lru for one)
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What does this PR do?
Optimizes the glob matching and limits the memory taken up by the LRU match cache.
Motivation
A follow up PR for bigger performance questions that came up in #1927 as well as bounding the cache memory for the LRU cache that came up in a security review.
How to test the change?
Unit tests and benchmarks are in the PR.