bench(hashline): added recovery session-chain replay throughput bench

Pins the hot path PR #1422 hardened: Recovery.tryRecover → applyEditsToSnapshot (3-way merge fails) → replaySessionChainOnCurrent → verifyAnchorContent. Two regimes (accept/reject) × three file sizes (50/500/5000 lines) × two anchor counts (1/8). Sanity-probes each case once before timing so the numbers measure the right branch. Surfaces the four-split-per-replay cost in the gated path; dedup is an obvious follow-up at large file sizes but out of scope here.
2026-05-26 22:03:06 -07:00
parent 621aff533a
commit 68a0fb61f9
1 changed files with 133 additions and 0 deletions
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+/**
+ * Recovery hot-path benchmark.
+ *
+ * Pin throughput of the session-chain replay path that PR #1422 hardened.
+ * After the fix, every replay call walks each edit's anchors and splits both
+ * `previousText` and `currentText` to compare per-line content. This bench
+ * exists so future optimisation of that walk has a baseline, and so reviewers
+ * can confirm the gate is cheap relative to the diff + applyPatch work that
+ * dominates the path.
+ *
+ * Two regimes:
+ *   - `accept` — anchor lands on a line unchanged across the prior in-session
+ *     edit. 3-way merge on the snapshot still fails (patch context spans the
+ *     rewritten neighbour), the new gate passes, and replay onto current
+ *     succeeds. End-to-end this exercises diff + applyPatch + applyEdits +
+ *     verifyAnchorContent.
+ *   - `reject` — anchor lands on the line the prior edit rewrote. 3-way merge
+ *     fails, the new gate refuses, and `tryRecover` returns null without
+ *     touching `applyEdits`. This is the corruption window PR #1422 closed
+ *     and the path users hit when re-targeting stale lines.
+ *
+ * Sizes (50/500/5000 lines) × edit batch (1/8 anchors) so the O(N) split cost
+ * in `verifyAnchorContent` and the O(K) anchor walk both surface.
+ */
+import { computeFileHash, InMemorySnapshotStore, parsePatch, Recovery } from "../src";
+
+const ITERATIONS = Number(Bun.env.HASHLINE_BENCH_ITERATIONS ?? "5000");
+const PATH = "/tmp/__hashline-recovery-bench__.ts";
+
+interface Fixture {
+	store: InMemorySnapshotStore;
+	v1Text: string;
+	h0: string;
+}
+
+/**
+ * Seed two snapshots: v0 → v1 where v1 differs only at `rewrittenLine`. The
+ * recovery driver will fetch v0 by hash and replay onto v1.
+ */
+function seed(lines: number, rewrittenLine: number): Fixture {
+	const v0Lines = Array.from({ length: lines }, (_, i) => `line ${i + 1} content`);
+	const v1Lines = [...v0Lines];
+	v1Lines[rewrittenLine - 1] = `line ${rewrittenLine} REWRITTEN`;
+	const v0Text = `${v0Lines.join("\n")}\n`;
+	const v1Text = `${v1Lines.join("\n")}\n`;
+	const h0 = computeFileHash(v0Text);
+	const h1 = computeFileHash(v1Text);
+	const store = new InMemorySnapshotStore();
+	store.recordContiguous(PATH, 1, v0Text.split("\n"), { fullText: v0Text, fileHash: h0 });
+	store.recordContiguous(PATH, 1, v1Text.split("\n"), { fullText: v1Text, fileHash: h1 });
+	return { store, v1Text, h0 };
+}
+
+/** Build an N-anchor edit batch whose anchor lines are distinct rows. */
+function batchPatch(anchors: readonly number[]): string {
+	return anchors.map(line => `${line}-${line}:\n+line ${line} MODEL`).join("\n");
+}
+
+interface Case {
+	name: string;
+	lines: number;
+	anchors: number[];
+	rewrittenLine: number;
+}
+
+const cases: Case[] = [];
+for (const size of [50, 500, 5000] as const) {
+	const rewritten = Math.floor(size / 2);
+	// Anchors spread across the file so verifyAnchorContent must walk real
+	// distances, not just hammer the same cache line.
+	const sparse = [Math.max(1, Math.floor(size / 8))];
+	const dense = [
+		Math.max(1, Math.floor(size / 9)),
+		Math.max(1, Math.floor(size / 8)),
+		Math.max(1, Math.floor(size / 7)),
+		Math.max(1, Math.floor(size / 6)),
+		Math.max(1, Math.floor(size / 5)),
+		Math.max(1, Math.floor(size / 4)),
+		Math.max(1, Math.floor(size / 3)),
+		Math.max(2, Math.floor((size * 2) / 3)),
+	];
+	cases.push(
+		{ name: `accept ${size}L ×1 anchor`, lines: size, anchors: sparse, rewrittenLine: rewritten },
+		{ name: `accept ${size}L ×8 anchors`, lines: size, anchors: dense, rewrittenLine: rewritten },
+		{ name: `reject ${size}L ×1 anchor`, lines: size, anchors: [rewritten], rewrittenLine: rewritten },
+	);
+}
+
+function bench(name: string, fn: () => void): { totalMs: number; perOpUs: number } {
+	// Warm: JIT + InMemorySnapshotStore LRU touches.
+	for (let i = 0; i < Math.min(50, ITERATIONS); i++) fn();
+	const start = Bun.nanoseconds();
+	for (let i = 0; i < ITERATIONS; i++) fn();
+	const elapsed = Bun.nanoseconds() - start;
+	const totalMs = elapsed / 1e6;
+	const perOpUs = elapsed / ITERATIONS / 1e3;
+	console.log(`  ${name.padEnd(28)}  ${totalMs.toFixed(2).padStart(8)}ms  ${perOpUs.toFixed(3).padStart(8)}µs/op`);
+	return { totalMs, perOpUs };
+}
+
+console.log(`Recovery session-chain replay (${ITERATIONS} iterations per case)`);
+console.log("Path: Recovery.tryRecover → applyEditsToSnapshot (3-way merge fails)");
+console.log("      → replaySessionChainOnCurrent → verifyAnchorContent (new gate)\n");
+
+let expectedNonNullVerified = 0;
+let expectedNullVerified = 0;
+
+for (const c of cases) {
+	const isReject = c.name.startsWith("reject");
+	const { store, v1Text, h0 } = seed(c.lines, c.rewrittenLine);
+	const recovery = new Recovery(store);
+	const { edits } = parsePatch(batchPatch(c.anchors));
+	const args = { path: PATH, currentText: v1Text, fileHash: h0, edits };
+
+	// Sanity: every iteration must hit the expected branch. Otherwise the
+	// numbers measure the wrong path.
+	const probe = recovery.tryRecover(args);
+	if (isReject) {
+		if (probe !== null) throw new Error(`expected null for ${c.name}, got recovery`);
+		expectedNullVerified++;
+	} else {
+		if (probe === null) throw new Error(`expected recovery for ${c.name}, got null`);
+		expectedNonNullVerified++;
+	}
+
+	bench(c.name, () => {
+		recovery.tryRecover(args);
+	});
+}
+
+console.log(
+	`\nSanity: ${expectedNonNullVerified} accept-path + ${expectedNullVerified} reject-path branches verified before timing.`,
+);