M9: benchmarks, chunked sorted map and JSON clone for the in-memory driver

Profiling showed document updates dominated by O(n) sorted-array splices; the
chunked map makes inserts O(log n + chunk). Baselines recorded in DESIGN.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017Qxbkp4tA7G5SCWjzWuxmE

bench/documents.bench.ts

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+import { bench, describe } from 'vitest'
+import { InMemoryKVDriver } from '../src/kv/memory.js'
+import { KVStorage } from '../src/kv/node.js'
+import { KVEventStorage } from '../src/events/kv.js'
+import { EventSourcedDocumentStorage } from '../src/documents/event-sourced.js'
+
+const N = 10_000
+const docs = new EventSourcedDocumentStorage(new KVEventStorage(new KVStorage(new InMemoryKVDriver())), {
+  indexes: { users: [{ fields: ['age'] }, { fields: ['email'], unique: true }] },
+  warnOnFullScan: false,
+})
+const users = docs.child('users')
+for (let i = 0; i < N; i++) await users.set(`u${i}`, { name: `user ${i}`, email: `u${i}@x.io`, age: i % 100, city: `c${i % 50}` })
+let i = 0
+
+describe(`documents @ ${N / 1000}k docs`, () => {
+  bench('get', async () => {
+    await users.get(`u${i++ % N}`)
+  })
+  bench('update ($inc, indexed node)', async () => {
+    await users.update(`u${i++ % N}`, { $inc: { logins: 1 } })
+  })
+  bench('findOne by unique index (email)', async () => {
+    await users.findOne({ email: `u${i++ % N}@x.io` })
+  })
+  bench('find indexed (age = k, ~100 hits)', async () => {
+    for await (const _ of users.find({ age: i++ % 100 })) {
+    }
+  })
+  bench('find full scan (city = k, ~200 hits)', async () => {
+    for await (const _ of users.find({ city: `c${i++ % 50}` })) {
+    }
+  })
+})

bench/events.bench.ts

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+import { bench, describe } from 'vitest'
+import { InMemoryKVDriver } from '../src/kv/memory.js'
+import { KVStorage } from '../src/kv/node.js'
+import { KVEventStorage } from '../src/events/kv.js'
+
+const events = new KVEventStorage(new KVStorage(new InMemoryKVDriver()))
+const streams = events.child('streams')
+const long = streams.child('long')
+for (let i = 0; i < 10_000; i++) await long.append([{ type: 'tick', i }])
+let s = 0
+
+describe('events', () => {
+  bench('append 1 event (warm head cache)', async () => {
+    await streams.append(`s${s++ % 1000}`, [{ type: 'e' }])
+  })
+  bench('read 100 events from version 5000 of 10k', async () => {
+    for await (const _ of long.read({ from: 5000, limit: 100 })) {
+    }
+  })
+  bench('read full 10k-event stream', async () => {
+    for await (const _ of long.read()) {
+    }
+  })
+  bench('version() (cold head lookup)', async () => {
+    await long.version()
+  })
+})

bench/keys.bench.ts

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+import { bench, describe } from 'vitest'
+import { InMemoryKVDriver } from '../src/kv/memory.js'
+import { KVStorage } from '../src/kv/node.js'
+
+// 1k children, each with 100 descendants (100k keys under the node).
+const db = new KVStorage(new InMemoryKVDriver({ clone: false }))
+const node = db.child('n')
+const writes: [string, number][] = []
+for (let c = 0; c < 1000; c++) {
+  writes.push([`n/c${c}`, c])
+  for (let d = 0; d < 100; d++) writes.push([`n/c${c}/d${d}`, d])
+}
+await db.driver.setMany(writes)
+
+describe('keys() on 1k children x 100 descendants', () => {
+  bench('keys() skip-scan', async () => {
+    let n = 0
+    for await (const _ of node.keys()) n++
+    if (n !== 1000) throw new Error(`expected 1000, got ${n}`)
+  })
+  bench('naive full subtree scan (reference)', async () => {
+    let n = 0
+    for await (const _ of db.driver.scan({ gte: 'n/', lt: 'n0' })) n++
+    if (n !== 101_000) throw new Error(`expected 101000, got ${n}`)
+  })
+})

bench/kv.bench.ts

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+import { bench, describe } from 'vitest'
+import { InMemoryKVDriver } from '../src/kv/memory.js'
+import { KVStorage } from '../src/kv/node.js'
+
+async function populated(n: number) {
+  const db = new KVStorage(new InMemoryKVDriver())
+  const users = db.child('users')
+  const batch: [string, { name: string; n: number }][] = []
+  for (let i = 0; i < n; i++) batch.push([`u${i}`, { name: `user ${i}`, n: i }])
+  await users.setMany(batch)
+  return users
+}
+
+for (const n of [10_000, 100_000]) {
+  const users = await populated(n)
+  const keys = Array.from({ length: 100 }, (_, i) => `u${(i * 7919) % n}`)
+  let i = 0
+  describe(`KV @ ${n / 1000}k keys`, () => {
+    bench('get', async () => {
+      await users.get(`u${i++ % n}`)
+    })
+    bench('set (overwrite)', async () => {
+      await users.set(`u${i++ % n}`, { name: 'x', n: i })
+    })
+    bench('getMany x100', async () => {
+      await users.getMany(keys)
+    })
+  })
+}