Store merged symbols in a paged symbol link store by jakebailey · Pull Request #64869 · microsoft/TypeScript

Jake Bailey (jakebailey) · 2026-10-19T17:23:36Z

getMergedSymbol runs on nearly every symbol access, and almost every call misses because few symbols are merge sources. Each miss still paid for a pointer-keyed map hash and probe.

Indexing by dense symbol ID makes the common miss a range check and a page load.

--checkers 4, n=8, default GC settings:

                  │  before    │              after               │
                  │   sec/op   │   sec/op    vs base              │
Tsc/bluesky         2.799 ± 2%   2.767 ± 1%       ~ (p=0.266 n=8)
Tsc/sentry          10.86 ± 2%   10.78 ± 2%       ~ (p=0.314 n=8)
Tsc/t3code-server   13.89 ± 6%   13.50 ± 4%  -2.85% (p=0.050 n=8)
geomean             7.502        7.384       -1.58%

                  │   before     │               after                │
                  │    rss-B     │    rss-B      vs base              │
Tsc/bluesky         1.203Gi ± 2%   1.183Gi ± 2%       ~ (p=0.291 n=8)
Tsc/sentry          3.535Gi ± 6%   3.549Gi ± 6%       ~ (p=1.000 n=8)
Tsc/t3code-server   2.877Gi ± 3%   2.880Gi ± 2%       ~ (p=0.721 n=8)
geomean             2.304Gi        2.296Gi       -0.37%

                  │   before     │               after                │
                  │    heap-B    │    heap-B     vs base              │
Tsc/bluesky         934.8Mi ± 0%   934.5Mi ± 0%  -0.04% (p=0.038 n=8)
Tsc/sentry          2.603Gi ± 0%   2.608Gi ± 0%  +0.16% (p=0.000 n=8)
Tsc/t3code-server   2.312Gi ± 0%   2.301Gi ± 0%  -0.45% (p=0.000 n=8)
geomean             1.765Gi        1.763Gi       -0.11%

getMergedSymbol runs on nearly every symbol access, and almost every call misses because few symbols are merge sources. Each miss still paid for a pointer-keyed map hash and probe. Indexing by dense symbol ID makes the common miss a range check and a page load. --checkers 4, n=8, default GC settings: │ before │ after │ │ sec/op │ sec/op vs base │ Tsc/bluesky 2.799 ± 2% 2.767 ± 1% ~ (p=0.266 n=8) Tsc/sentry 10.86 ± 2% 10.78 ± 2% ~ (p=0.314 n=8) Tsc/t3code-server 13.89 ± 6% 13.50 ± 4% -2.85% (p=0.050 n=8) geomean 7.502 7.384 -1.58% │ before │ after │ │ rss-B │ rss-B vs base │ Tsc/bluesky 1.203Gi ± 2% 1.183Gi ± 2% ~ (p=0.291 n=8) Tsc/sentry 3.535Gi ± 6% 3.549Gi ± 6% ~ (p=1.000 n=8) Tsc/t3code-server 2.877Gi ± 3% 2.880Gi ± 2% ~ (p=0.721 n=8) geomean 2.304Gi 2.296Gi -0.37% │ before │ after │ │ heap-B │ heap-B vs base │ Tsc/bluesky 934.8Mi ± 0% 934.5Mi ± 0% -0.04% (p=0.038 n=8) Tsc/sentry 2.603Gi ± 0% 2.608Gi ± 0% +0.16% (p=0.000 n=8) Tsc/t3code-server 2.312Gi ± 0% 2.301Gi ± 0% -0.45% (p=0.000 n=8) geomean 1.765Gi 1.763Gi -0.11%

Copilot

🟢 Approval recommended

The focused storage substitution preserves lookup behavior, with no unresolved findings.

No open issues 🎉

What changed in this PR

Replaces the checker’s merged-symbol map with an existing paged store indexed by symbol ID to reduce lookup overhead.

Changes:

Uses a zero-initialized symbolLinkStore instead of an explicitly initialized map.
Updates reads and writes while preserving fallback to the original symbol.

File	Description
`tsc/internal/checker/checker.go`	Migrates merged-symbol storage and access to the paged store.

_{Review effort: Balanced}

Jake Bailey (jakebailey) · 2026-10-19T17:37:02Z

TypeScript Bot (@typescript-bot) perf test this faster

typescript-automation · 2026-10-19T17:37:09Z

Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
`perf test this faster`	✅ Started	👀 Results

typescript-automation · 2026-10-19T18:11:22Z

Jake Bailey (@jakebailey)
The results of the perf run you requested are in!

Here they are:

tsc

Comparison Report - baseline..pr

_Metric	_baseline	_pr	_Delta	_Best	_Worst	_p-value
_{Compiler-Unions - native}
_Errors	₄₁	₄₁	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_115,276	_115,276	_~	_~	_~	_{p=1.000 n=12}
_Types	_79,613	_79,613	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{113,563k (± 0.06%)}	_{113,253k (± 0.06%)}	_{-310k (- 0.27%)}	_113,064k	_113,457k	_{p=0.000 n=12}
_{Memory Allocs}	_{2,212,530 (± 0.01%)}	_{2,212,347 (± 0.00%)}	_~	_2,212,078	_2,212,592	_{p=0.068 n=12}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.049s (± 3.00%)}	_{0.049s (± 3.75%)}	_~	_0.043s	_0.052s	_{p=0.943 n=12}
_{Bind Time}	_{0.016s (±12.17%)}	_{0.016s (± 9.21%)}	_~	_0.014s	_0.020s	_{p=0.826 n=12}
_{Check Time}	_{0.565s (± 0.80%)}	_{0.557s (± 0.79%)}	_{-0.007s (- 1.28%)}	_0.547s	_0.570s	_{p=0.018 n=12}
_{Emit Time}	_{0.316s (± 2.18%)}	_{0.320s (± 2.42%)}	_~	_0.299s	_0.345s	_{p=0.504 n=12}
_{Total Time}	_{0.954s (± 0.80%)}	_{0.950s (± 0.98%)}	_~	_0.927s	_0.976s	_{p=0.541 n=12}
_{angular-1 - native}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_{846,745 (± 0.06%)}	_{847,065 (± 0.09%)}	_~	_844,684	_848,703	_{p=0.410 n=12}
_Types	_{247,032 (± 0.00%)}	_{247,033 (± 0.00%)}	_~	_247,030	_247,042	_{p=0.530 n=12}
_{Memory Used}	_{596,418k (± 0.03%)}	_{597,202k (± 0.03%)}	_{+784k (+ 0.13%)}	_596,779k	_597,876k	_{p=0.000 n=12}
_{Memory Allocs}	_{13,139,814 (± 0.02%)}	_{13,148,529 (± 0.08%)}	_~	_13,137,054	_13,179,984	_{p=0.143 n=12}
_{Config Time}	_{0.020s (± 1.40%)}	_{0.020s (± 1.21%)}	_~	_0.020s	_0.021s	_{p=1.000 n=12}
_{Parse Time}	_{0.281s (± 2.06%)}	_{0.282s (± 2.86%)}	_~	_0.264s	_0.304s	_{p=1.000 n=12}
_{Bind Time}	_{0.099s (±14.09%)}	_{0.099s (±13.92%)}	_~	_0.073s	_0.135s	_{p=0.854 n=12}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=12}
_{Emit Time}	_{1.866s (± 0.89%)}	_{1.859s (± 1.49%)}	_~	_1.794s	_1.933s	_{p=0.434 n=12}
_{Total Time}	_{2.287s (± 1.00%)}	_{2.282s (± 1.40%)}	_~	_2.195s	_2.367s	_{p=0.701 n=12}
_{mui-docs - native}
_Errors	_11,405	_11,405	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_4,331,983	_4,331,983	_~	_~	_~	_{p=1.000 n=12}
_Types	_1,370,520	_1,370,520	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{2,625,154k (± 0.06%)}	_{2,625,505k (± 0.05%)}	_~	_2,621,533k	_2,629,646k	_{p=0.932 n=12}
_{Memory Allocs}	_{27,707,952 (± 0.08%)}	_{27,705,555 (± 0.06%)}	_~	_27,651,291	_27,748,504	_{p=0.713 n=12}
_{Config Time}	_{0.020s (± 1.52%)}	_{0.020s (± 1.40%)}	_~	_0.020s	_0.021s	_{p=1.000 n=12}
_{Parse Time}	_{0.589s (± 2.89%)}	_{0.569s (± 1.94%)}	_~	_0.541s	_0.601s	_{p=0.066 n=12}
_{Bind Time}	_{0.003s (±12.54%)}	_{0.003s (± 8.64%)}	_~	_0.002s	_0.003s	_{p=0.371 n=12}
_{Check Time}	_{8.634s (± 0.38%)}	_{8.581s (± 0.28%)}	_{-0.053s (- 0.61%)}	_8.543s	_8.685s	_{p=0.004 n=12}
_{Emit Time}	_{0.669s (±12.27%)}	_{0.739s (± 9.36%)}	_~	_0.502s	_0.794s	_{p=0.271 n=12}
_{Total Time}	_{10.820s (± 0.94%)}	_{10.823s (± 0.58%)}	_~	_10.551s	_10.898s	_{p=0.319 n=12}
_{strada-build-src - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,388,680	_1,388,680	_~	_~	_~	_{p=1.000 n=12}
_Types	_441,862	_441,862	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{1,313,037k (± 0.68%)}	_{1,316,360k (± 0.51%)}	_~	_1,303,824k	_1,335,513k	_{p=0.347 n=12}
_{Memory Allocs}	_{78,272,951 (± 0.04%)}	_{78,208,042 (± 0.09%)}	_~	_78,013,324	_78,389,819	_{p=0.089 n=12}
_{Config Time}	_{0.004s (±13.98%)}	_{0.004s (±18.02%)}	_~	_0.002s	_0.006s	_{p=0.577 n=12}
_{Parse Time}	_{0.313s (± 1.93%)}	_{0.309s (± 2.12%)}	_~	_0.289s	_0.326s	_{p=0.297 n=12}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{1.996s (± 0.47%)}	_{1.981s (± 0.44%)}	_{-0.015s (- 0.74%)}	_1.960s	_2.005s	_{p=0.037 n=12}
_{Emit Time}	_{0.359s (± 4.53%)}	_{0.356s (± 3.15%)}	_~	_0.333s	_0.392s	_{p=0.799 n=12}
_{Total Time}	_{23.868s (± 0.74%)}	_{23.684s (± 0.37%)}	_{-0.184s (- 0.77%)}	_23.457s	_23.958s	_{p=0.039 n=12}
_{strada-compiler - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_334,953	_334,953	_~	_~	_~	_{p=1.000 n=12}
_Types	_197,616	_197,616	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{247,451k (± 0.02%)}	_{246,597k (± 0.02%)}	_{-853k (- 0.34%)}	_246,463k	_246,729k	_{p=0.000 n=12}
_{Memory Allocs}	_{4,329,273 (± 0.01%)}	_{4,328,676 (± 0.01%)}	_{-597 (- 0.01%)}	_4,327,716	_4,329,486	_{p=0.017 n=12}
_{Config Time}	_{0.000s (±113.79%)}	_{0.001s (±65.70%)}	_~	_0.000s	_0.001s	_{p=0.400 n=12}
_{Parse Time}	_{0.091s (± 4.22%)}	_{0.088s (± 6.18%)}	_~	_0.078s	_0.099s	_{p=0.213 n=12}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Check Time}	_{0.799s (± 0.60%)}	_{0.785s (± 0.63%)}	_{-0.014s (- 1.79%)}	_0.776s	_0.801s	_{p=0.001 n=12}
_{Emit Time}	_{0.119s (± 8.82%)}	_{0.123s (± 8.71%)}	_~	_0.085s	_0.142s	_{p=0.468 n=12}
_{Total Time}	_{1.056s (± 0.86%)}	_{1.042s (± 1.02%)}	_~	_1.017s	_1.064s	_{p=0.080 n=12}
_{ts-pre-modules - native}
_Errors	₈₇	₈₇	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_303,834	_303,834	_~	_~	_~	_{p=1.000 n=12}
_Types	_181,663	_181,663	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{215,230k (± 0.02%)}	_{214,663k (± 0.02%)}	_{-567k (- 0.26%)}	_214,574k	_214,807k	_{p=0.000 n=12}
_{Memory Allocs}	_{1,401,610 (± 0.02%)}	_{1,401,339 (± 0.01%)}	_~	_1,400,945	_1,401,818	_{p=0.128 n=12}
_{Config Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.097s (± 2.24%)}	_{0.097s (± 4.22%)}	_~	_0.086s	_0.107s	_{p=0.680 n=12}
_{Bind Time}	_{0.039s (± 9.53%)}	_{0.045s (± 9.87%)}	_{🔻+0.005s (+14.04%)}	_0.030s	_0.052s	_{p=0.032 n=12}
_{Check Time}	_{0.746s (± 0.92%)}	_{0.734s (± 0.91%)}	_{-0.012s (- 1.65%)}	_0.721s	_0.761s	_{p=0.014 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{0.897s (± 0.65%)}	_{0.890s (± 0.73%)}	_~	_0.877s	_0.915s	_{p=0.108 n=12}
_{vscode - native}
_Errors	₃₉₆	₃₉₆	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_12,386,876	_12,386,876	_~	_~	_~	_{p=1.000 n=12}
_Types	_4,049,733	_4,049,733	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{5,821,308k (± 0.02%)}	_{5,816,151k (± 0.02%)}	_{-5,157k (- 0.09%)}	_5,814,651k	_5,818,452k	_{p=0.000 n=12}
_{Memory Allocs}	_{59,185,764 (± 0.01%)}	_{59,183,471 (± 0.01%)}	_~	_59,174,370	_59,220,265	_{p=0.347 n=12}
_{Config Time}	_0.076s	_{0.076s (± 0.43%)}	_{+0.001s (+ 0.66%)}	_0.076s	_0.077s	_{p=0.014 n=12}
_{Parse Time}	_{1.812s (± 2.74%)}	_{1.839s (± 1.95%)}	_~	_1.721s	_1.907s	_{p=0.164 n=12}
_{Bind Time}	_{0.726s (±14.37%)}	_{0.648s (±12.00%)}	_~	_0.513s	_0.917s	_{p=0.319 n=12}
_{Check Time}	_{15.584s (± 1.02%)}	_{15.419s (± 1.02%)}	_~	_15.109s	_15.741s	_{p=0.089 n=12}
_{Emit Time}	_{5.465s (± 7.30%)}	_{5.599s (± 7.40%)}	_~	_4.530s	_6.423s	_{p=0.579 n=12}
_{Total Time}	_{23.752s (± 1.41%)}	_{23.672s (± 1.44%)}	_~	_22.699s	_24.356s	_{p=0.799 n=12}
_{webpack - native}
_Errors	₅₉₈	₅₉₈	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,398,302	_1,398,302	_~	_~	_~	_{p=1.000 n=12}
_Types	_670,900	_670,900	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{885,667k (± 0.01%)}	_{886,476k (± 0.02%)}	_{+809k (+ 0.09%)}	_885,960k	_886,859k	_{p=0.000 n=12}
_{Memory Allocs}	_{6,925,456 (± 0.01%)}	_{6,928,389 (± 0.04%)}	_{+2,932 (+ 0.04%)}	_6,925,119	_6,941,872	_{p=0.001 n=12}
_{Config Time}	_0.009s	_0.009s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.316s (± 1.35%)}	_{0.308s (± 3.79%)}	_~	_0.276s	_0.344s	_{p=0.173 n=12}
_{Bind Time}	_{0.080s (± 8.82%)}	_{0.083s (±14.02%)}	_~	_0.072s	_0.138s	_{p=0.680 n=12}
_{Check Time}	_{2.971s (± 0.56%)}	_{2.887s (± 0.47%)}	_{-0.084s (- 2.83%)}	_2.841s	_2.916s	_{p=0.000 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{3.414s (± 0.40%)}	_{3.325s (± 0.49%)}	_{-0.089s (- 2.61%)}	_3.285s	_3.358s	_{p=0.000 n=12}
_{xstate-main - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=12}
_Symbols	_1,060,810	_1,060,810	_~	_~	_~	_{p=1.000 n=12}
_Types	_389,671	_389,671	_~	_~	_~	_{p=1.000 n=12}
_{Memory Used}	_{471,970k (± 0.03%)}	_{472,299k (± 0.03%)}	_{+329k (+ 0.07%)}	_472,016k	_472,657k	_{p=0.000 n=12}
_{Memory Allocs}	_{4,224,017 (± 0.08%)}	_{4,219,966 (± 0.07%)}	_~	_4,211,791	_4,228,347	_{p=0.089 n=12}
_{Config Time}	_0.002s	_0.002s	_~	_~	_~	_{p=1.000 n=12}
_{Parse Time}	_{0.109s (± 2.69%)}	_{0.105s (± 3.76%)}	_~	_0.095s	_0.115s	_{p=0.090 n=12}
_{Bind Time}	_{0.031s (±16.52%)}	_{0.039s (±17.28%)}	_~	_0.027s	_0.050s	_{p=0.057 n=12}
_{Check Time}	_{0.914s (± 0.86%)}	_{0.897s (± 0.72%)}	_{-0.016s (- 1.81%)}	_0.887s	_0.918s	_{p=0.002 n=12}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=12}
_{Total Time}	_{1.061s (± 0.88%)}	_{1.049s (± 0.63%)}	_{-0.012s (- 1.15%)}	_1.031s	_1.062s	_{p=0.027 n=12}

System info unknown

Hosts

native

Scenarios

Compiler-Unions - native
angular-1 - native
mui-docs - native
strada-build-src - native
strada-compiler - native
ts-pre-modules - native
vscode - native
webpack - native
xstate-main - native

_Benchmark	_Name	_Iterations
_Current	_pr	₁₂
_Baseline	_baseline	₁₂

Developer Information:

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Copilot AI balanced review requested due to automatic review settings October 19, 2026 17:23

github-project-automation Bot added this to PR Backlog Oct 19, 2026

typescript-automation Bot assigned Jake Bailey (jakebailey) Oct 19, 2026

typescript-automation Bot added Author: Team For Uncommitted Bug PR for untriaged, rejected, closed or missing bug labels Oct 19, 2026

github-project-automation Bot moved this to Not started in PR Backlog Oct 19, 2026

Copilot started reviewing on behalf of Jake Bailey (jakebailey) October 19, 2026 17:24

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Store merged symbols in a paged symbol link store - #64869

Store merged symbols in a paged symbol link store#64869
Jake Bailey (jakebailey) wants to merge 1 commit into
microsoft:mainfrom
jakebailey:perf/paged-merged-symbols

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