Cloudflare durable object storage latency repro: test by visiting `/whatever?transact=select-1&n=1`, or `/whatever?transact=no-op&n=1`, and `/whatever?transact=local-no-op`

index.ts

import { DurableObject } from "cloudflare:workers";
import { z } from "zod/v4";

const transactMethod = z
  .enum(["transaction", "sync-sql", "blockConcurrencyWhile", "racy", "no-op", "select-1", "local-no-op"])
  .default("sync-sql");

export class MyDurableObject extends DurableObject<Env> {
  constructor(ctx: DurableObjectState, env: Env) {
    super(ctx, env);
    this.ctx.blockConcurrencyWhile(async () => {
      // this.ctx.storage.sql.exec("DROP TABLE IF EXISTS vars");
      this.ctx.storage.sql.exec("CREATE TABLE IF NOT EXISTS vars(key integer primary key, value integer)");
    });
  }

  async perform(id: number, method: z.infer<typeof transactMethod>) {
    let counter: number;
    if (method === "transaction")
      await this.ctx.storage.transaction(async () => {
        this.ctx.storage.sql.exec("INSERT INTO vars (key, value) VALUES (?, 0) ON CONFLICT DO NOTHING", id);
        counter = this.ctx.storage.sql.exec("SELECT * FROM vars WHERE key = ?", id).one().value as number;
        await new Promise((resolve) => setTimeout(resolve, 100));
        this.ctx.storage.sql.exec("UPDATE vars SET value = ? WHERE key = ?", counter + 1, id);
      });
    else if (method === "sync-sql") {
      this.ctx.storage.sql.exec("INSERT INTO vars (key, value) VALUES (?, 0) ON CONFLICT DO NOTHING", id);
      counter = this.ctx.storage.sql.exec("SELECT * FROM vars WHERE key = ?", id).one().value as number;
      this.ctx.storage.sql.exec("UPDATE vars SET value = ? WHERE key = ?", counter + 1, id);
    } else if (method === "blockConcurrencyWhile")
      await this.ctx.blockConcurrencyWhile(async () => {
        this.ctx.storage.sql.exec("INSERT INTO vars (key, value) VALUES (?, 0) ON CONFLICT DO NOTHING", id);
        counter = this.ctx.storage.sql.exec("SELECT * FROM vars WHERE key = ?", id).one().value as number;
        await new Promise((resolve) => setTimeout(resolve, 100));
        this.ctx.storage.sql.exec("UPDATE vars SET value = ? WHERE key = ?", counter + 1, id);
      });
    else if (method === "racy") {
      this.ctx.storage.sql.exec("INSERT INTO vars (key, value) VALUES (?, 0) ON CONFLICT DO NOTHING", id);
      counter = this.ctx.storage.sql.exec("SELECT * FROM vars WHERE key = ?", id).one().value as number;
      await new Promise((resolve) => setTimeout(resolve, 100));
      this.ctx.storage.sql.exec("UPDATE vars SET value = ? WHERE key = ?", counter + 1, id);
    } else if (method === "select-1") {
      this.ctx.storage.sql.exec("INSERT INTO vars (key, value) VALUES (?, 0)", Math.round(Math.random() * 10000));
      counter = this.ctx.storage.sql.exec("SELECT * FROM vars LIMIT 1").one().value as number;
    } else {
      counter = 0;
    }
    return counter! + 1;
  }
}

export default {
  async fetch(request: Request, env: Env, ctx: ExecutionContext) {
    const url = new URL(request.url);
    if (url.pathname === "/favicon.ico") return new Response(null, { status: 404 });

    const id: DurableObjectId = env.MY_DURABLE_OBJECT.idFromName(new URL(request.url).pathname);
    const stub = env.MY_DURABLE_OBJECT.get(id);

    const transact = transactMethod.safeParse(url.searchParams.get("transact") ?? undefined);
    const requests = z.coerce
      .number()
      .pipe(z.int())
      .default(10)
      .safeParse(url.searchParams.get("n") ?? undefined);

    if (transact.error || requests.error) return new Response(null, { status: 400 });

    if (transact.data === "local-no-op") return new Response("OK");

    const promises = await Promise.all(Array.from({ length: requests.data }, () => stub.perform(2, transact.data)));

    return new Response(`parallel results: ${promises}`);
  },
} satisfies ExportedHandler<Env>;

package.json

{
  "name": "workers-play",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "private": true,
  "keywords": [],
  "author": "",
  "license": "ISC",
  "packageManager": "[email protected]",
  "devDependencies": {
    "@cloudflare/vitest-pool-workers": "^0.8.34",
    "typescript": "^5.8.3",
    "vitest": "^3.1.4",
    "wrangler": "^4.18.0"
  },
  "dependencies": {
    "zod": "^3.25.42"
  }
}

tsconfig.json

{
  "compilerOptions": {
    /* Visit https://aka.ms/tsconfig.json to read more about this file */

    /* Set the JavaScript language version for emitted JavaScript and include compatible library declarations. */
    "target": "es2021",
    /* Specify a set of bundled library declaration files that describe the target runtime environment. */
    "lib": ["es2021"],

    /* Specify what module code is generated. */
    "module": "es2022",
    /* Specify how TypeScript looks up a file from a given module specifier. */
    "moduleResolution": "Bundler",
    /* Enable importing .json files */
    "resolveJsonModule": true,

    /* Allow JavaScript files to be a part of your program. Use the `checkJS` option to get errors from these files. */
    "allowJs": true,
    /* Enable error reporting in type-checked JavaScript files. */
    "checkJs": false,

    /* Disable emitting files from a compilation. */
    "noEmit": true,

    /* Ensure that each file can be safely transpiled without relying on other imports. */
    "isolatedModules": true,
    /* Allow 'import x from y' when a module doesn't have a default export. */
    "allowSyntheticDefaultImports": true,
    /* Ensure that casing is correct in imports. */
    "forceConsistentCasingInFileNames": true,

    /* Enable all strict type-checking options. */
    "strict": true,

    /* Skip type checking all .d.ts files. */
    "skipLibCheck": true
  },
  "exclude": ["test"],
  "include": ["worker-configuration.d.ts", "src/**/*.ts"]
}

wrangler.toml

name = "main"
compatibility_date = "2025-05-30"
main = "index.ts"

[durable_objects]
bindings = [
  { name = "MY_DURABLE_OBJECT", class_name = "MyDurableObject" },
]

[[migrations]]
tag = "v1"
new_sqlite_classes = ["MyDurableObject"]

[observability]
enabled = true
head_sampling_rate = 1

[placement]
mode = "smart"