perf: use shallow dup instead of deep_dup for Scope and BreadcrumbBuffer#2907
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perf: use shallow dup instead of deep_dup for Scope and BreadcrumbBuffer#2907
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⚠️ Needs closer review — changes copy semantics for scope containers. Replace deep_dup with dup for Scope's contexts, extra, tags, user, and fingerprint hashes, and for BreadcrumbBuffer's buffer array. Rationale: These containers are not mutated in-place after duplication. Scope methods like set_tags, set_extras, set_user all use assignment (replacing the entire hash) or merge! on the copy's own hash. The inner values (strings, numbers, symbols) are immutable or treated as such. BreadcrumbBuffer: Individual Breadcrumb objects in the buffer are not mutated after being recorded — they are only read during serialization. A shallow dup of the buffer array is sufficient to prevent the copy from seeing new breadcrumbs added to the original. span, session, and propagation_context still use deep_dup as they contain mutable nested state that may be modified in-place.
HazAT
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Mar 18, 2026
Reduce total allocated memory from 442k to 206k bytes (-53.5%) and
objects from 3305 to 1538 (-53.5%) per Rails exception capture.
All changes are internal optimizations with zero behavior changes.
Key optimizations:
- Cache longest_load_path and compute_filename results (class-level,
invalidated on $LOAD_PATH changes)
- Cache backtrace line parsing and Line/Frame object creation (bounded
at 2048 entries)
- Optimize LineCache with Hash#fetch, direct context setting, and
per-(filename, lineno) caching
- Avoid unnecessary allocations: indexed regex captures, match? instead
of =~, byteslice, single-pass iteration in StacktraceBuilder
- RequestInterface: avoid env.dup, cache header name transforms, ASCII
fast-path for encoding
- Scope/BreadcrumbBuffer: shallow dup instead of deep_dup where inner
values are not mutated after duplication
- Hub#add_breadcrumb: hint default nil instead of {} to avoid empty
hash allocation
See sub-PRs for detailed review by risk level:
- #2902 (low risk) — hot path allocation avoidance
- #2903 (low risk) — LineCache optimization
- #2904 (medium risk) — load path and filename caching
- #2905 (needs review) — backtrace parse caching
- #2906 (needs review) — Frame object caching
- #2907 (needs review) — Scope/BreadcrumbBuffer shallow dup
- #2908 (medium risk) — RequestInterface optimizations
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don't want to risk this and the % change in allocation is not that high. |
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Part of #2901 (reduce memory allocations by ~53%)
Changes
Replace
deep_dupwithdupfor:contexts,extra,tags,user,fingerprintbufferarrayRationale
Scope: These containers are not mutated in-place after duplication. Scope methods like
set_tags,set_extras,set_userall use assignment (replacing the entire hash) ormerge!on the copy's own hash. The inner values (strings, numbers, symbols) are immutable or treated as such.BreadcrumbBuffer: Individual
Breadcrumbobjects in the buffer are not mutated after being recorded — they are only read during serialization. A shallowdupof the buffer array is sufficient to prevent the copy from seeing new breadcrumbs added to the original.span,session, andpropagation_contextstill usedeep_dupas they contain mutable nested state that may be modified in-place.Review focus
contexts/extra/tags/userare mutated in-place (rather than replaced)?