Default to GOGC=50 by jakebailey · Pull Request #4401 · microsoft/typescript-go

jakebailey · 2026-06-22T22:18:56Z

I had copilot do an analysis of a spread of GOGC values, building an LSP harness and testing it on the old compiler source, and then a tsc run on the old compiler and VS Code. https://gist.github.com/jakebailey/1fb4a89bead2dcef0f51e7a4cbdcdec7

The gist is that GOGC=50 seems to provide a reasonable peak memory savings without too much extra CPU time. Wall time is in general unaffected, just since Go's GC is concurrent, so can do work while idle.

This needs more testing, but it seems like 50 is probably a good default.

jakebailey · 2026-06-22T22:19:07Z

@typescript-bot perf test this

typescript-automation · 2026-06-22T22:19:12Z

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

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

Copilot

Pull request overview

This PR sets a lower default Go GC target for the tsgo executable to reduce peak memory usage by default, while still allowing users to override GC behavior via the existing GOGC environment variable.

Changes:

Add core.ApplyDefaultGOGC() to set runtime/debug.SetGCPercent(50) when GOGC is not set.
Invoke core.ApplyDefaultGOGC() early in cmd/tsgo startup so it applies to all tsgo modes (tsc, --lsp, --api).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
internal/core/core.go	Adds helper to apply a default `GOGC` value when not configured by the environment.
cmd/tsgo/main.go	Calls the new helper during `tsgo` startup to apply the default GC percent.

typescript-automation · 2026-06-22T22:45:48Z

@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	₄	₄	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_{81,764 (± 0.02%)}	_{81,789 (± 0.01%)}	_{+25 (+ 0.03%)}	_81,777	_81,806	_{p=0.045 n=6}
_Types	_98,821	_98,821	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{180,334k (± 0.34%)}	_{180,820k (± 0.49%)}	_~	_180,055k	_182,474k	_{p=0.810 n=6}
_{Memory Allocs}	_{2,546,337 (± 0.01%)}	_{2,547,347 (± 0.01%)}	_{+1,010 (+ 0.04%)}	_2,546,856	_2,547,835	_{p=0.005 n=6}
_{Config Time}	_{0.001s (±109.43%)}	_{0.001s (±109.43%)}	_~	_0.000s	_0.001s	_{p=1.000 n=6}
_{Parse Time}	_{0.059s (± 4.84%)}	_{0.068s (± 1.71%)}	_{🔻+0.009s (+14.57%)}	_0.067s	_0.070s	_{p=0.005 n=6}
_{Bind Time}	_{0.020s (±17.56%)}	_{0.020s (±10.49%)}	_~	_0.018s	_0.023s	_{p=0.808 n=6}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Emit Time}	_{1.023s (± 1.26%)}	_{1.075s (± 1.44%)}	_{🔻+0.052s (+ 5.08%)}	_1.046s	_1.086s	_{p=0.005 n=6}
_{Total Time}	_{1.104s (± 1.25%)}	_{1.165s (± 1.33%)}	_{🔻+0.061s (+ 5.54%)}	_1.136s	_1.177s	_{p=0.005 n=6}
_{angular-1 - native}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_{876,981 (± 0.03%)}	_{876,357 (± 0.10%)}	_~	_874,742	_877,207	_{p=0.173 n=6}
_Types	_{263,749 (± 0.00%)}	_{263,750 (± 0.00%)}	_~	_263,748	_263,753	_{p=0.662 n=6}
_{Memory Used}	_{830,795k (± 0.06%)}	_{830,945k (± 0.09%)}	_~	_830,038k	_832,188k	_{p=0.936 n=6}
_{Memory Allocs}	_{12,596,265 (± 0.06%)}	_{12,606,030 (± 0.13%)}	_~	_12,589,804	_12,631,856	_{p=0.378 n=6}
_{Config Time}	_{0.025s (±13.62%)}	_{0.030s (±12.81%)}	_{🔻+0.005s (+19.87%)}	_0.024s	_0.036s	_{p=0.044 n=6}
_{Parse Time}	_{0.265s (± 4.79%)}	_{0.316s (± 4.01%)}	_{🔻+0.051s (+19.27%)}	_0.298s	_0.335s	_{p=0.005 n=6}
_{Bind Time}	_{0.042s (±12.90%)}	_{0.062s (±21.97%)}	_{🔻+0.020s (+46.85%)}	_0.047s	_0.078s	_{p=0.013 n=6}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Emit Time}	_{2.103s (± 0.47%)}	_{2.227s (± 1.59%)}	_{🔻+0.125s (+ 5.92%)}	_2.181s	_2.286s	_{p=0.005 n=6}
_{Total Time}	_{2.450s (± 0.79%)}	_{2.656s (± 1.53%)}	_{🔻+0.206s (+ 8.39%)}	_2.602s	_2.711s	_{p=0.005 n=6}
_{mui-docs - native}
_Errors	_{11,279 (± 0.07%)}	_{11,277 (± 0.07%)}	_~	_11,265	_11,283	_{p=0.864 n=6}
_Symbols	_4,214,838	_4,214,838	_~	_~	_~	_{p=1.000 n=6}
_Types	_1,534,279	_1,534,279	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{4,963,494k (± 0.02%)}	_{4,964,916k (± 0.04%)}	_~	_4,963,292k	_4,967,913k	_{p=0.230 n=6}
_{Memory Allocs}	_{87,688,341 (±23.24%)}	_{97,999,248 (±20.59%)}	_~	_74,854,109	_124,583,865	_{p=0.298 n=6}
_{Config Time}	_{0.026s (±10.37%)}	_{0.033s (± 5.07%)}	_{🔻+0.007s (+25.32%)}	_0.031s	_0.035s	_{p=0.005 n=6}
_{Parse Time}	_{1.165s (±28.62%)}	_{1.573s (±25.85%)}	_~	_1.158s	_2.150s	_{p=0.128 n=6}
_{Bind Time}	_{0.002s (±18.82%)}	_0.002s	_~	_~	_~	_{p=0.405 n=6}
_{Check Time}	_{19.639s (± 0.78%)}	_{20.658s (± 0.57%)}	_{🔻+1.019s (+ 5.19%)}	_20.488s	_20.774s	_{p=0.005 n=6}
_{Emit Time}	_{0.548s (± 4.86%)}	_{0.533s (± 4.18%)}	_~	_0.524s	_0.579s	_{p=0.806 n=6}
_{Total Time}	_{22.227s (± 1.37%)}	_{23.698s (± 1.82%)}	_{🔻+1.471s (+ 6.62%)}	_23.243s	_24.343s	_{p=0.005 n=6}
_{self-build-src - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,394,138	_1,394,138	_~	_~	_~	_{p=1.000 n=6}
_Types	_442,153	_442,153	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{1,654,938k (± 0.38%)}	_{1,653,139k (± 0.26%)}	_~	_1,646,445k	_1,657,886k	_{p=0.575 n=6}
_{Memory Allocs}	_{97,847,871 (± 0.06%)}	_{97,911,414 (± 0.04%)}	_~	_97,840,865	_97,958,087	_{p=0.093 n=6}
_{Config Time}	_{0.024s (±17.64%)}	_{0.055s (±10.77%)}	_{🔻+0.031s (+131.69%)}	_0.048s	_0.063s	_{p=0.005 n=6}
_{Parse Time}	_{0.248s (± 4.13%)}	_{0.314s (± 4.17%)}	_{🔻+0.066s (+26.75%)}	_0.302s	_0.330s	_{p=0.005 n=6}
_{Bind Time}	_0.000s	_{0.000s (±244.70%)}	_~	_0.000s	_0.001s	_{p=0.405 n=6}
_{Check Time}	_{2.676s (± 1.04%)}	_{2.820s (± 1.33%)}	_{🔻+0.144s (+ 5.38%)}	_2.763s	_2.848s	_{p=0.005 n=6}
_{Emit Time}	_{0.338s (± 2.25%)}	_{0.386s (± 8.89%)}	_{🔻+0.048s (+14.25%)}	_0.339s	_0.427s	_{p=0.025 n=6}
_{Total Time}	_{34.313s (± 0.71%)}	_{36.294s (± 1.49%)}	_{🔻+1.981s (+ 5.77%)}	_35.686s	_37.058s	_{p=0.005 n=6}
_{self-compiler - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_337,634	_337,634	_~	_~	_~	_{p=1.000 n=6}
_Types	_199,520	_199,520	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{332,292k (± 0.02%)}	_{332,356k (± 0.04%)}	_~	_332,205k	_332,545k	_{p=0.378 n=6}
_{Memory Allocs}	_{4,725,443 (± 0.02%)}	_{4,732,303 (± 0.03%)}	_{+6,860 (+ 0.15%)}	_4,729,895	_4,734,179	_{p=0.005 n=6}
_{Config Time}	_0.001s	_{0.002s (±55.72%)}	_~	_0.001s	_0.003s	_{p=0.176 n=6}
_{Parse Time}	_{0.124s (± 6.52%)}	_{0.144s (± 4.37%)}	_{🔻+0.021s (+16.55%)}	_0.135s	_0.151s	_{p=0.006 n=6}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{1.372s (± 0.65%)}	_{1.410s (± 1.03%)}	_{+0.039s (+ 2.82%)}	_1.391s	_1.432s	_{p=0.005 n=6}
_{Emit Time}	_{0.123s (± 4.27%)}	_{0.140s (± 7.23%)}	_{🔻+0.017s (+13.82%)}	_0.127s	_0.150s	_{p=0.030 n=6}
_{Total Time}	_{1.676s (± 0.41%)}	_{1.756s (± 0.90%)}	_{🔻+0.080s (+ 4.78%)}	_1.735s	_1.783s	_{p=0.005 n=6}
_{ts-pre-modules - native}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_97,488	_97,488	_~	_~	_~	_{p=1.000 n=6}
_Types	₃₅₆	₃₅₆	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{133,743k (± 0.02%)}	_{133,716k (± 0.01%)}	_~	_133,697k	_133,734k	_{p=0.128 n=6}
_{Memory Allocs}	_{183,058 (± 0.13%)}	_{188,311 (± 1.19%)}	_{+5,253 (+ 2.87%)}	_183,819	_189,649	_{p=0.005 n=6}
_{Config Time}	_0.001s	_{0.001s (±48.94%)}	_~	_0.000s	_0.001s	_{p=0.405 n=6}
_{Parse Time}	_{0.113s (± 7.35%)}	_{0.122s (± 3.08%)}	_~	_0.118s	_0.128s	_{p=0.078 n=6}
_{Bind Time}	_{0.041s (±13.58%)}	_{0.045s (± 6.77%)}	_~	_0.039s	_0.048s	_{p=0.193 n=6}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{0.157s (± 3.58%)}	_{0.172s (± 3.73%)}	_{🔻+0.015s (+ 9.34%)}	_0.164s	_0.180s	_{p=0.008 n=6}
_{vscode - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_6,691,256	_6,691,256	_~	_~	_~	_{p=1.000 n=6}
_Types	_2,374,896	_2,374,896	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{4,574,360k (± 0.02%)}	_{4,574,709k (± 0.03%)}	_~	_4,572,926k	_4,576,273k	_{p=0.575 n=6}
_{Memory Allocs}	_{32,130,719 (± 0.05%)}	_{32,139,386 (± 0.06%)}	_~	_32,116,950	_32,168,121	_{p=0.378 n=6}
_{Config Time}	_{0.069s (±10.20%)}	_{0.088s (± 6.55%)}	_{🔻+0.019s (+27.36%)}	_0.082s	_0.098s	_{p=0.006 n=6}
_{Parse Time}	_{0.888s (± 4.18%)}	_{1.006s (± 3.55%)}	_{🔻+0.118s (+13.23%)}	_0.953s	_1.049s	_{p=0.005 n=6}
_{Bind Time}	_{0.137s (± 3.18%)}	_{0.190s (±36.28%)}	_~	_0.131s	_0.295s	_{p=0.747 n=6}
_{Check Time}	_{9.088s (± 0.20%)}	_{9.389s (± 0.57%)}	_{+0.301s (+ 3.31%)}	_9.310s	_9.463s	_{p=0.005 n=6}
_{Emit Time}	_{2.506s (± 1.62%)}	_{2.408s (± 1.45%)}	_{🟩-0.098s (- 3.90%)}	_2.347s	_2.438s	_{p=0.005 n=6}
_{Total Time}	_{12.704s (± 0.21%)}	_{13.102s (± 0.44%)}	_{+0.398s (+ 3.14%)}	_13.010s	_13.189s	_{p=0.005 n=6}
_{webpack - native}
_Errors	₂	₂	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_182,879	_182,879	_~	_~	_~	_{p=1.000 n=6}
_Types	₃₄₀	₃₄₀	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{221,792k (± 0.11%)}	_{221,637k (± 0.11%)}	_~	_221,376k	_221,960k	_{p=0.173 n=6}
_{Memory Allocs}	_{1,066,103 (± 0.27%)}	_{1,089,398 (± 0.70%)}	_{+23,295 (+ 2.19%)}	_1,078,736	_1,097,641	_{p=0.005 n=6}
_{Config Time}	_{0.012s (±19.02%)}	_{0.014s (±12.13%)}	_~	_0.012s	_0.017s	_{p=0.088 n=6}
_{Parse Time}	_{0.149s (± 5.36%)}	_{0.200s (± 2.99%)}	_{🔻+0.051s (+34.45%)}	_0.193s	_0.207s	_{p=0.005 n=6}
_{Bind Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Emit Time}	_{0.043s (±20.32%)}	_{0.055s (±11.48%)}	_{🔻+0.013s (+29.80%)}	_0.049s	_0.064s	_{p=0.031 n=6}
_{Total Time}	_{0.204s (± 5.53%)}	_{0.272s (± 4.32%)}	_{🔻+0.067s (+32.98%)}	_0.259s	_0.288s	_{p=0.005 n=6}
_{xstate-main - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,065,023	_1,065,023	_~	_~	_~	_{p=1.000 n=6}
_Types	_389,185	_389,185	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{642,826k (± 0.01%)}	_{642,866k (± 0.02%)}	_~	_642,688k	_643,035k	_{p=0.575 n=6}
_{Memory Allocs}	_{5,054,667 (± 0.06%)}	_{5,084,294 (± 0.52%)}	_{+29,627 (+ 0.59%)}	_5,065,554	_5,124,284	_{p=0.005 n=6}
_{Config Time}	_{0.002s (±18.82%)}	_0.003s	_{🔻+0.001s (+38.46%)}	_~	_~	_{p=0.007 n=6}
_{Parse Time}	_{0.125s (±10.39%)}	_{0.159s (±10.98%)}	_{🔻+0.033s (+26.76%)}	_0.136s	_0.174s	_{p=0.013 n=6}
_{Bind Time}	_{0.028s (±42.22%)}	_{0.041s (±24.06%)}	_{🔻+0.014s (+50.30%)}	_0.035s	_0.061s	_{p=0.043 n=6}
_{Check Time}	_{1.122s (± 0.81%)}	_{1.161s (± 0.68%)}	_{+0.038s (+ 3.43%)}	_1.149s	_1.170s	_{p=0.005 n=6}
_{Emit Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{1.282s (± 1.40%)}	_{1.368s (± 1.37%)}	_{🔻+0.086s (+ 6.74%)}	_1.334s	_1.389s	_{p=0.005 n=6}

System info unknown

Hosts

native

Scenarios

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

_Benchmark	_Name	_Iterations
_Current	_pr	₆
_Baseline	_baseline	₆

lsp

Comparison Report - baseline..pr

_Metric	_baseline	_pr	_Delta	_Best	_Worst	_p-value
_{Compiler-UnionsLSP - native}
_{Req 1 - updateOpen}	_{10ms (± 4.01%)}	_{10ms (± 6.32%)}	_~	_9ms	_11ms	_{p=0.673 n=6}
_{Req 2 - geterr}	_{979ms (± 0.90%)}	_{990ms (± 1.00%)}	_~	_982ms	_1,009ms	_{p=0.125 n=6}
_{Req 3 - references}	_{42ms (±11.65%)}	_{40ms (± 8.53%)}	_~	_36ms	_45ms	_{p=0.462 n=6}
_{Req 4 - navto}	_{17ms (± 7.26%)}	_{17ms (± 6.80%)}	_~	_16ms	_19ms	_{p=0.563 n=6}
_{Req 5 - completionInfo count}	_1,357	_1,357	_~	_~	_~	_{p=1.000 n=6}
_{Req 5 - completionInfo}	_{15ms (±13.32%)}	_{18ms (±18.21%)}	_~	_13ms	_22ms	_{p=0.091 n=6}
_{CompilerLSP - native}
_{Req 1 - updateOpen}	_{11ms (± 9.07%)}	_{10ms (± 4.99%)}	_~	_10ms	_11ms	_{p=0.417 n=6}
_{Req 2 - geterr}	_{460ms (± 1.51%)}	_{479ms (± 2.06%)}	_{🔻+20ms (+ 4.24%)}	_469ms	_496ms	_{p=0.010 n=6}
_{Req 3 - references}	_{48ms (± 5.35%)}	_{50ms (±12.29%)}	_~	_44ms	_61ms	_{p=0.868 n=6}
_{Req 4 - navto}	_17ms	_{18ms (± 5.99%)}	_~	_16ms	_19ms	_{p=0.293 n=6}
_{Req 5 - completionInfo count}	_1,519	_1,519	_~	_~	_~	_{p=1.000 n=6}
_{Req 5 - completionInfo}	_{22ms (± 7.22%)}	_{20ms (±22.39%)}	_~	_13ms	_24ms	_{p=0.225 n=6}

System info unknown

Hosts

native

Scenarios

CompilerLSP - native
Compiler-UnionsLSP - native
xstate-main-1-LSP - native

_Benchmark	_Name	_Iterations
_Current	_pr	₆
_Baseline	_baseline	₆

startup

Comparison Report - baseline..pr

_Metric	_baseline	_pr	_Delta	_Best	_Worst	_p-value
_{lsp-startup - native}
_{Execution time}	_{4.90ms (±516.54%)}	_{4.94ms (±516.55%)}	_~	_0.00ms	_501.25ms	_{p=0.072 n=600}
_{tsgo-startup - native}
_{Execution time}	_{6.05ms (±516.55%)}	_{6.09ms (±516.54%)}	_{+0.04ms (+ 0.59%)}	_0.00ms	_610.86ms	_{p=0.000 n=600}

System info unknown

Hosts

native

Scenarios

lsp-startup - native
tsgo-startup - native

_Benchmark	_Name	_Iterations
_Current	_pr	₆
_Baseline	_baseline	₆

Developer Information:

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jakebailey · 2026-06-22T22:46:17Z

Huh... Worse?

jakebailey · 2026-06-22T22:46:49Z

Well, more worse than I was expecting anyway

Default to GOGC=50

c2e4114

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Default to GOGC=50#4401

Default to GOGC=50#4401
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tsc

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startup

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typescript-automation Bot commented Jun 22, 2026

tsc

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startup

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