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orca/config/scripts/command-code-transcript-scan-benchmark.mjs
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#!/usr/bin/env node
// Compare mirrored Command Code prompt readers on the per-tool-hook path: capped 4MB full parse versus backward chunks returning at the latest user line.
// Typical prompts are near EOF; read constants from production so cap drift fails instead of measuring stale code.
import {
closeSync,
mkdtempSync,
openSync,
readFileSync,
readSync,
rmSync,
statSync,
writeFileSync
} from 'node:fs'
import { tmpdir } from 'node:os'
import { join } from 'node:path'
import { performance } from 'node:perf_hooks'
import { fileURLToPath } from 'node:url'
const LISTENER_SOURCE = readFileSync(
fileURLToPath(
new URL(
'../../src/shared/agent-hook-listener/normalization/normalize-hook-payload.ts',
import.meta.url
)
),
'utf8'
)
function readMirroredConstant(name) {
const match = LISTENER_SOURCE.match(new RegExp(`const ${name} = ([^\\n]+)`))
if (!match) {
throw new Error(`agent-hook-listener.ts no longer defines ${name}; re-sync this benchmark.`)
}
const value = Number(new Function(`return (${match[1]})`)())
if (!Number.isInteger(value) || value <= 0) {
throw new Error(`${name} did not resolve to a positive integer`)
}
return value
}
const TRANSCRIPT_CHUNK_BYTES = readMirroredConstant('TRANSCRIPT_CHUNK_BYTES')
const TRANSCRIPT_MAX_SCAN_BYTES = readMirroredConstant('TRANSCRIPT_MAX_SCAN_BYTES')
const EMPTY_REGION = Buffer.alloc(0)
const ITERATIONS = Number.parseInt(process.env.ORCA_CC_SCAN_BENCH_ITERATIONS ?? '150', 10)
const WARMUP = Number.parseInt(process.env.ORCA_CC_SCAN_BENCH_WARMUP ?? '20', 10)
for (const [name, value] of [
['ORCA_CC_SCAN_BENCH_ITERATIONS', ITERATIONS],
['ORCA_CC_SCAN_BENCH_WARMUP', WARMUP]
]) {
if (!Number.isInteger(value) || value <= 0) {
throw new Error(`${name} must be a positive integer, received ${value}`)
}
}
// Mirror parseAgentHookJson’s structural scan in BOTH arms; omitting it made baseline ~9x too fast and invented a regression.
const HOOK_STRUCTURAL_TOKENS = 128 * 1024
const HOOK_NESTING_DEPTH = 64
function assertJsonStructure(content) {
let structuralTokens = 0
let depth = 0
let inString = false
let escaped = false
for (let index = 0; index < content.length; index += 1) {
const character = content[index]
if (inString) {
if (escaped) {
escaped = false
} else if (character === '\\') {
escaped = true
} else if (character === '"') {
inString = false
}
continue
}
if (character === '"') {
inString = true
continue
}
if (
character !== '{' &&
character !== '}' &&
character !== '[' &&
character !== ']' &&
character !== ',' &&
character !== ':'
) {
continue
}
structuralTokens += 1
if (structuralTokens > HOOK_STRUCTURAL_TOKENS) {
throw new Error('structuralTokens')
}
if (character === '{' || character === '[') {
depth += 1
if (depth > HOOK_NESTING_DEPTH) {
throw new Error('nestingDepth')
}
} else if (character === '}' || character === ']') {
depth = Math.max(0, depth - 1)
}
}
}
function extractUserPrompt(line) {
let entry
try {
assertJsonStructure(line)
entry = JSON.parse(line)
} catch {
return undefined
}
if (typeof entry !== 'object' || entry === null || entry.role !== 'user') {
return undefined
}
const content = entry.content
if (typeof content === 'string' && content.trim().length > 0) {
return content
}
if (Array.isArray(content)) {
for (const part of content) {
if (typeof part === 'object' && part !== null) {
const text = part.text
if (typeof text === 'string' && text.trim().length > 0) {
return text
}
}
}
}
return undefined
}
function readForward(path) {
const size = statSync(path).size
if (size <= 0) {
return undefined
}
const bytesToRead = Math.min(size, TRANSCRIPT_MAX_SCAN_BYTES)
const position = size - bytesToRead
const fd = openSync(path, 'r')
try {
const buffer = Buffer.alloc(bytesToRead)
let filled = 0
while (filled < bytesToRead) {
const n = readSync(fd, buffer, filled, bytesToRead - filled, position + filled)
if (n === 0) {
break
}
filled += n
}
let text = buffer.subarray(0, filled).toString('utf8')
if (position > 0) {
const firstNewline = text.indexOf('\n')
text = firstNewline === -1 ? '' : text.slice(firstNewline + 1)
}
let last
for (const line of text.split('\n')) {
const prompt = extractUserPrompt(line.trim())
if (prompt !== undefined) {
last = prompt
}
}
return last
} finally {
closeSync(fd)
}
}
function findLastPromptInRegion(region) {
let lineEnd = region.length
for (let index = region.length - 1; index >= -1; index--) {
if (index >= 0 && region[index] !== 0x0a) {
continue
}
const lineStart = index + 1
if (lineEnd > lineStart) {
const prompt = extractUserPrompt(region.subarray(lineStart, lineEnd).toString('utf8').trim())
if (prompt !== undefined) {
return prompt
}
}
lineEnd = index
}
return undefined
}
// Backward scan carries chunk lists; repeatedly joining an oversized line would become quadratic.
function readBackward(path) {
const size = statSync(path).size
if (size <= 0) {
return undefined
}
const fd = openSync(path, 'r')
try {
let carryChunks = []
let bytesRead = 0
let scanEnd = size
while (scanEnd > 0 && bytesRead < TRANSCRIPT_MAX_SCAN_BYTES) {
const chunkSize = Math.min(
scanEnd,
TRANSCRIPT_CHUNK_BYTES,
TRANSCRIPT_MAX_SCAN_BYTES - bytesRead
)
const position = scanEnd - chunkSize
const buffer = Buffer.alloc(chunkSize)
let filled = 0
while (filled < chunkSize) {
const n = readSync(fd, buffer, filled, chunkSize - filled, position + filled)
if (n === 0) {
break
}
filled += n
}
if (filled < chunkSize) {
break
}
bytesRead += filled
scanEnd = position
const firstNewline = buffer.indexOf(0x0a)
const atStart = position === 0
let completeRegion
if (atStart) {
completeRegion = carryChunks.length === 0 ? buffer : Buffer.concat([buffer, ...carryChunks])
carryChunks = []
} else if (firstNewline === -1) {
completeRegion = EMPTY_REGION
carryChunks.unshift(buffer)
} else {
const afterNewline = buffer.subarray(firstNewline + 1)
completeRegion =
carryChunks.length === 0 ? afterNewline : Buffer.concat([afterNewline, ...carryChunks])
carryChunks = [buffer.subarray(0, firstNewline)]
}
if (completeRegion.length > 0) {
const found = findLastPromptInRegion(completeRegion)
if (found !== undefined) {
return found
}
}
}
return undefined
} finally {
closeSync(fd)
}
}
// Model completed turns followed by current prompt/output so the answer sits near EOF.
function writeTranscript(path, priorTurns) {
const lines = []
for (let index = 0; index < priorTurns; index += 1) {
lines.push(
JSON.stringify({ role: 'user', content: [{ type: 'text', text: `older turn ${index}` }] })
)
lines.push(
JSON.stringify({
role: 'assistant',
content: [{ type: 'text', text: `${'assistant output '.repeat(30)}${index}` }]
})
)
}
lines.push(
JSON.stringify({ role: 'user', content: [{ type: 'text', text: 'the current prompt' }] })
)
for (let index = 0; index < 40; index += 1) {
lines.push(
JSON.stringify({
role: 'assistant',
content: [{ type: 'text', text: `${'current turn output '.repeat(30)}${index}` }]
})
)
}
writeFileSync(path, `${lines.join('\n')}\n`)
}
// Trailing tool output determines how far backward the current turn’s scan must walk.
function writeTranscriptWithTrailing(path, priorTurns, trailingBytes) {
const lines = []
for (let index = 0; index < priorTurns; index += 1) {
lines.push(
JSON.stringify({ role: 'user', content: [{ type: 'text', text: `older turn ${index}` }] })
)
lines.push(
JSON.stringify({
role: 'assistant',
content: [{ type: 'text', text: `${'assistant output '.repeat(30)}${index}` }]
})
)
}
lines.push(
JSON.stringify({ role: 'user', content: [{ type: 'text', text: 'the current prompt' }] })
)
let written = 0
let index = 0
while (written < trailingBytes) {
const line = JSON.stringify({
role: 'assistant',
content: [{ type: 'text', text: `${'current turn output '.repeat(30)}${index}` }]
})
lines.push(line)
written += line.length + 1
index += 1
}
writeFileSync(path, `${lines.join('\n')}\n`)
}
// Oversized tool result removes newline stops across many read blocks.
function writeTranscriptWithHugeLine(path, lineBytes) {
const lines = [
JSON.stringify({ role: 'user', content: [{ type: 'text', text: 'the current prompt' }] }),
JSON.stringify({ role: 'assistant', content: [{ type: 'text', text: 'x'.repeat(lineBytes) }] })
]
writeFileSync(path, `${lines.join('\n')}\n`)
}
function measure(fn, path) {
for (let index = 0; index < WARMUP; index += 1) {
fn(path)
}
const samples = []
for (let round = 0; round < 3; round += 1) {
const start = performance.now()
for (let index = 0; index < ITERATIONS; index += 1) {
fn(path)
}
samples.push((performance.now() - start) / ITERATIONS)
}
samples.sort((a, b) => a - b)
return samples[1]
}
const dir = mkdtempSync(join(tmpdir(), 'orca-cc-transcript-bench-'))
try {
const rows = []
for (const priorTurns of [250, 1000, 3000, 6000]) {
const path = join(dir, `transcript-${priorTurns}.jsonl`)
writeTranscript(path, priorTurns)
const forward = readForward(path)
const backward = readBackward(path)
if (forward !== backward) {
throw new Error(`prompt mismatch at ${priorTurns} prior turns: ${forward} vs ${backward}`)
}
if (backward !== 'the current prompt') {
throw new Error(`benchmark fixture resolved the wrong prompt: ${backward}`)
}
rows.push({
sizeMb: statSync(path).size / (1024 * 1024),
beforeMs: measure(readForward, path),
afterMs: measure(readBackward, path)
})
}
const pad = (value, width) => String(value).padStart(width)
console.log('Command Code transcript prompt read, per hook event')
console.log(`iterations=${ITERATIONS} warmup=${WARMUP} (median of 3 rounds)`)
console.log(
`${pad('size', 9)} ${pad('before ms', 11)} ${pad('after ms', 10)} ${pad('speedup', 9)}`
)
for (const row of rows) {
console.log(
`${pad(`${row.sizeMb.toFixed(2)} MB`, 9)} ${pad(row.beforeMs.toFixed(3), 11)} ${pad(row.afterMs.toFixed(3), 10)} ${pad(`${(row.beforeMs / row.afterMs).toFixed(0)}x`, 9)}`
)
}
console.log(
'\nThe old cost grows with the transcript; the new cost is flat because the\ncurrent turn’s prompt sits near EOF and the scan stops at the first hit.'
)
// Report worst cases too: cost follows bytes after prompt, so long turns/oversized results can erase or invert the win.
const worst = []
for (const trailingKb of [32, 256, 1024, 3072]) {
const path = join(dir, `trailing-${trailingKb}.jsonl`)
writeTranscriptWithTrailing(path, 1500, trailingKb * 1024)
if (readForward(path) !== readBackward(path)) {
throw new Error(`prompt mismatch at trailing ${trailingKb} KB`)
}
worst.push({
label: `${(trailingKb / 1024).toFixed(2)} MB after prompt`,
beforeMs: measure(readForward, path),
afterMs: measure(readBackward, path)
})
}
const hugePath = join(dir, 'huge-line.jsonl')
writeTranscriptWithHugeLine(hugePath, 3 * 1024 * 1024)
if (readForward(hugePath) !== readBackward(hugePath)) {
throw new Error('prompt mismatch on the oversized-line fixture')
}
worst.push({
label: '3 MB single line',
beforeMs: measure(readForward, hugePath),
afterMs: measure(readBackward, hugePath)
})
console.log('\nWorst cases (win decays as a turn progresses; <1x means slower):')
console.log(
`${pad('case', 22)} ${pad('before ms', 11)} ${pad('after ms', 10)} ${pad('ratio', 9)}`
)
for (const row of worst) {
console.log(
`${pad(row.label, 22)} ${pad(row.beforeMs.toFixed(3), 11)} ${pad(row.afterMs.toFixed(3), 10)} ${pad(`${(row.beforeMs / row.afterMs).toFixed(2)}x`, 9)}`
)
}
console.log(
'\nThe win shrinks toward parity as output accumulates after the prompt, since\nthe backward scan has to read past all of it. The single-line row is the floor:\nno newline to stop on, so the scan reads the line in blocks and joins once where\nthe old code issued one flat read. Both sides pay the same per-line structure\nscan, and the carry is a chunk list, so cost stays linear either way.'
)
} finally {
rmSync(dir, { recursive: true, force: true })
}