Optimize atomic snapshot transitions

[SandroMaglione]

Summary

• fast-path same-state atomic snapshot transitions in the compiled flat executor
• preserve schema decoding and lifecycle failures for invalid transition values
• avoid rebuilding a generic active configuration for the common target.full.State(...) update path

Changeset

• Added or updated for a library or package-metadata change
• Not required because this PR does not change src/ or package.json

Validation

• pnpm check
• Relevant example checks, when examples changed (no examples changed)
• Reviewed the automated type-performance report, when the public TypeScript API or inference changed (no public type change; pnpm perf:types passes)
• Reviewed the automated runtime-performance report, when runtime behavior changed

Local paired profiling showed approximately +31% flat burst throughput, +18% observed burst throughput, and +25% child delivery throughput. The automated report remains the merge gate.

[github-actions]

Type performance

Measured with TypeScript 6.0.3 and skipLibCheck=true.

Scenario	Base	PR	Difference
Effect only	55	55	0 (0.0%)
Import effect-machine	55	55	0 (0.0%)
Machine.defineStates (3 states)	2,965	2,965	0 (0.0%)
Machine.make (3 states, 2 events)	8,715	8,715	0 (0.0%)
machine.handle (3 states, 2 transitions)	23,492	23,492	0 (0.0%)
machine.handle (depth 8)	117,075	117,075	0 (0.0%)
machine.handle (depth 12)	129,713	129,713	0 (0.0%)
machine.handle (depth 16)	145,055	145,055	0 (0.0%)
machine.handle (depth 24)	183,851	183,851	0 (0.0%)
machine.handle (wide depth 16)	214,189	214,189	0 (0.0%)
machine.handle (parallel/history/choice)	132,667	132,667	0 (0.0%)
machine.handle (4 successive calls)	128,674	128,674	0 (0.0%)
machine exact input/output/error/services	110,584	110,584	0 (0.0%)
execution adapter readiness	127,854	127,854	0 (0.0%)

Marginal instantiations are measured against the matching setup without that API call:

Scenario	Base	PR	Difference
Import effect-machine	0	0	0
Machine.defineStates (3 states)	2,910	2,910	0 (0.0%)
Machine.make (3 states, 2 events)	5,742	5,742	0 (0.0%)
machine.handle (3 states, 2 transitions)	14,777	14,777	0 (0.0%)
machine.handle (depth 8)	109,601	109,601	0 (0.0%)
machine.handle (depth 12)	121,039	121,039	0 (0.0%)
machine.handle (depth 16)	135,181	135,181	0 (0.0%)
machine.handle (depth 24)	171,577	171,577	0 (0.0%)
machine.handle (wide depth 16)	202,224	202,224	0 (0.0%)
machine.handle (parallel/history/choice)	114,331	114,331	0 (0.0%)
machine.handle (4 successive calls)	113,703	113,703	0 (0.0%)
machine exact input/output/error/services	100,670	100,670	0 (0.0%)
execution adapter readiness	102,092	102,092	0 (0.0%)

Check times (informational)

Scenario	Base	PR
Effect only	0.03s	0.03s
Import effect-machine	0.03s	0.03s
Machine.defineStates (3 states)	0.10s	0.10s
Machine.make (3 states, 2 events)	0.16s	0.16s
machine.handle (3 states, 2 transitions)	0.25s	0.23s
machine.handle (depth 8)	0.51s	0.51s
machine.handle (depth 12)	0.56s	0.56s
machine.handle (depth 16)	0.60s	0.59s
machine.handle (depth 24)	0.70s	0.72s
machine.handle (wide depth 16)	0.80s	0.78s
machine.handle (parallel/history/choice)	0.64s	0.63s
machine.handle (4 successive calls)	0.60s	0.59s
machine exact input/output/error/services	0.57s	0.51s
execution adapter readiness	0.56s	0.59s

Type instantiations are the comparison metric. Check time varies with runner load and is informational only.

[github-actions]

Runtime performance

Median of 5 independent benchmark processes on AMD EPYC 9V74 80-Core Processor with Node v24.18.0.

Pull request baseline

Scenario	Effect Machine	XState 5	XState 6 alpha
Plan counter transitions	115,926 transitions/s	134,964 transitions/s	112,404 transitions/s
Drain burst with terminal fence	340,185 increments/s	378,867 increments/s	104,357 increments/s
Drain burst with a change observer	191,424 increments/s	374,647 increments/s	104,134 increments/s
Lookup and send to one child	289,675 increments/s	373,788 increments/s	100,860 increments/s
Start and stop a machine	35,421 machines/s	177,683 machines/s	72,569 machines/s
Start and stop a parent with one child	13,282 families/s	71,531 families/s	30,095 families/s
Drain burst through a compound state	279,540 events/s	332,142 events/s	103,653 events/s
Drain burst through two parallel regions	259,971 events/s	252,337 events/s	89,510 events/s

Effect runtime reference points

Scenario	Effect Machine	Effect runtime primitives
Start and stop a raw compiled process	40,640 processes/s	—
Start and interrupt a suspended fiber	—	157,011 fibers/s
Start and stop a queue worker	—	115,835 workers/s
Start and stop an actor shell	—	105,887 actors/s
Start and stop two actor shells	—	67,105 families/s
Update an owner-only mutable snapshot	—	312,012,480 updates/s
Update a synchronized snapshot	—	1,637,835 updates/s
Create, resolve, and await a terminal latch	—	1,650,097 latches/s

Memory profile	Effect Machine	XState 5	XState 6 alpha	Effect runtime primitives
Idle machine	2.0 KiB	3.8 KiB	6.1 KiB	—
Raw generic managed process	12.3 KiB	—	—	—
Raw compiled process	2.7 KiB	—	—	—
Two independent idle machines	3.5 KiB	7.3 KiB	11.8 KiB	—
Idle parent with one child	5.8 KiB	5.5 KiB	8.8 KiB	—
Parent with observed child registry	10.0 KiB	—	—	—
Parent with observed invoked child snapshots	6.0 KiB	—	—	—
Suspended Effect fiber	—	—	—	0.7 KiB
Effect queue with waiting fiber	—	—	—	2.8 KiB
Effect mailbox actor shell	—	—	—	3.2 KiB
Two Effect actor shells	—	—	—	6.9 KiB

Effect Machine change from base

Metric	Base	Base variability	PR	PR variability	Difference
Plan counter transitions	117,155 transitions/s	0.6% MAD	115,926 transitions/s	0.3% MAD	-1.0%
Drain burst with terminal fence	256,222 increments/s	4.0% MAD	340,185 increments/s	2.2% MAD	+32.8%
Drain burst with a change observer	166,594 increments/s	1.2% MAD	191,424 increments/s	0.6% MAD	+14.9%
Lookup and send to one child	228,729 increments/s	1.0% MAD	289,675 increments/s	1.4% MAD	+26.6%
Start and stop a machine	35,892 machines/s	0.9% MAD	35,421 machines/s	1.6% MAD	-1.3%
Start and stop a parent with one child	13,518 families/s	1.9% MAD	13,282 families/s	2.4% MAD	-1.7%
Drain burst through a compound state	275,219 events/s	1.2% MAD	279,540 events/s	0.3% MAD	+1.6%
Drain burst through two parallel regions	260,969 events/s	2.0% MAD	259,971 events/s	0.1% MAD	-0.4%
Idle machine heap per unit	2.0 KiB	0.0% MAD	2.0 KiB	0.0% MAD	0.0%
Raw generic managed process heap per unit	12.3 KiB	0.0% MAD	12.3 KiB	0.0% MAD	-0.1%
Raw compiled process heap per unit	2.7 KiB	0.0% MAD	2.7 KiB	0.0% MAD	0.0%
Two independent idle machines heap per unit	3.5 KiB	0.0% MAD	3.5 KiB	0.0% MAD	-0.1%
Idle parent with one child heap per unit	5.8 KiB	0.0% MAD	5.8 KiB	0.1% MAD	+0.5%
Parent with observed child registry heap per unit	10.0 KiB	0.0% MAD	10.0 KiB	0.0% MAD	+0.0%
Parent with observed invoked child snapshots heap per unit	6.0 KiB	0.0% MAD	6.0 KiB	0.0% MAD	+0.0%

Effect runtime reference change from base

Metric	Base	Base variability	PR	PR variability	Difference
Start and stop a raw compiled process	39,831 processes/s	1.4% MAD	40,640 processes/s	0.3% MAD	+2.0%
Start and interrupt a suspended fiber	157,754 fibers/s	0.2% MAD	157,011 fibers/s	0.9% MAD	-0.5%
Start and stop a queue worker	115,048 workers/s	0.6% MAD	115,835 workers/s	0.0% MAD	+0.7%
Start and stop an actor shell	104,123 actors/s	2.8% MAD	105,887 actors/s	2.2% MAD	+1.7%
Start and stop two actor shells	67,195 families/s	0.1% MAD	67,105 families/s	0.1% MAD	-0.1%
Update an owner-only mutable snapshot	312,012,480 updates/s	0.0% MAD	312,012,480 updates/s	0.0% MAD	0.0%
Update a synchronized snapshot	1,659,999 updates/s	1.5% MAD	1,637,835 updates/s	0.3% MAD	-1.3%
Create, resolve, and await a terminal latch	1,668,516 latches/s	1.2% MAD	1,650,097 latches/s	2.0% MAD	-1.1%

Versions and interpretation

• Effect Machine: 0.3.0
• XState 5: 5.32.5
• XState 6 alpha: 6.0.0-alpha.27
• Effect runtime primitives: 4.0.0-beta.105

Higher throughput is better; lower heap is better. Variability is the median absolute deviation across independent processes, relative to their median. Runtime measurements on shared GitHub-hosted hardware remain informational, so small differences should be confirmed across multiple workflow runs.