Checkpoint not reduce WAL to 0

[unrealhoang]

What happens?

I'm trying to build the feature to allow user to download their own DB file, and re-open them, but despite after checkpointing & close the db / connection, if I use that same DB file without the attached WAL, the DB will be put in read-only mode. Is this intentional, or should the WAL be empty? As from the docs:

If DuckDB exits normally, the WAL file is deleted upon exit. If DuckDB crashes, the WAL file is required to recover data.

Following is a minimal reproduce script:

To Reproduce

// app_load_db.js

// Import the Wasm file URIs
import * as duckdb from 'https://cdn.jsdelivr.net/npm/@duckdb/duckdb-wasm@1.29.1-dev132.0/+esm';

// === Configuration ===
const OPFS_DB_PATH = 'opfs://testduck.db';
const DB_FILE = 'testduck.db'; 

let db = null; // AsyncDuckDB instance
let conn = null; // Active connection to the OPFS database
let workerScriptText;
let bundle;

async function removeFiles() {
  const opfsRoot = await navigator.storage.getDirectory();

  await opfsRoot.removeEntry(DB_FILE).catch((e) => {
    console.error(e);
  });
  await opfsRoot.removeEntry(DB_FILE + '.wal').catch((e) => {
    console.error(e);
  });
  await opfsRoot.removeEntry('new.db').catch((e) => {
    console.error(e);
  });
  await opfsRoot.removeEntry('new.db.wal').catch((e) => {
    console.error(e);
  });
}

async function setup() {
  await removeFiles();
  let blobUrl = null;

  try {
    const bundles = duckdb.getJsDelivrBundles();
    bundle = await duckdb.selectBundle(bundles);
    console.log('Using bundle:', bundle);
    if (!bundle.mainWorker) throw new Error('Could not determine worker URL.');

    const workerResponse = await fetch(bundle.mainWorker);
    if (!workerResponse.ok) throw new Error(`Failed to fetch worker: ${workerResponse.statusText}`);
    workerScriptText = await workerResponse.text();
    const blob = new Blob([workerScriptText], { type: 'application/javascript' });
    blobUrl = URL.createObjectURL(blob);

    const worker = new Worker(blobUrl);
    const logger = new duckdb.ConsoleLogger(duckdb.LogLevel.WARNING);
    db = new duckdb.AsyncDuckDB(logger, worker);
    await db.instantiate(bundle.mainModule, bundle.pthreadWorker);

    await db.open({
      path: OPFS_DB_PATH,
      accessMode: duckdb.DuckDBAccessMode.READ_WRITE
    });
    conn = await db.connect();

    document.db = db; // Make accessible in console for debugging
    if (blobUrl) URL.revokeObjectURL(blobUrl);
  } catch (error) {
    if (blobUrl) URL.revokeObjectURL(blobUrl);
    console.error(error);
  }

  await conn.send(`CREATE TABLE tmp AS SELECT unnest(generate_series(1, 100)) as count`);
  await conn.send(`CHECKPOINT;`);
}

async function copyOpfsFile(opfsRoot, src, dst) {
  let srcFileHandle = await opfsRoot.getFileHandle(src, { create: false })
  let srcFile = await srcFileHandle.getFile();
  let dstFileHandle = await opfsRoot.getFileHandle(dst, { create: true });
  let writableDstFile = await dstFileHandle.createWritable();
  await srcFile.stream().pipeTo(writableDstFile);
}

async function test() {
  await conn.close();
  await db.reset();
  await db.terminate();

  const opfsRoot = await navigator.storage.getDirectory();
  copyOpfsFile(opfsRoot, DB_FILE, 'new.db')
  copyOpfsFile(opfsRoot, DB_FILE + '.wal', 'new.db.wal') // <-- comment out this line will cause the last create table to fail

  const blob = new Blob([workerScriptText], { type: 'application/javascript' });
  const blobUrl = URL.createObjectURL(blob);

  const worker = new Worker(blobUrl);
  const logger = new duckdb.ConsoleLogger(duckdb.LogLevel.WARNING);
  db = new duckdb.AsyncDuckDB(logger, worker);
  await db.instantiate(bundle.mainModule, bundle.pthreadWorker);
  await db.open({
    path: 'opfs://new.db',
    accessMode: duckdb.DuckDBAccessMode.READ_WRITE
  });
  conn = await db.connect();
  if (blobUrl) URL.revokeObjectURL(blobUrl);

  await query(`SELECT count(*)::INTEGER as cnt FROM tmp;`);
  await query('create table new as select 1 as b');
};

async function query(q) {
  const result = await conn.query(q);
  console.log(result.toArray().map(r => r.toJSON()));
}

await setup();
await test();

Browser/Environment:

Version 134.0.6998.166 (Official Build) (arm64)

Device:

Macbook M4 Pro

DuckDB-Wasm Version:

duckdb-wasm@1.29.1-dev132.0

DuckDB-Wasm Deployment:

localhost

Full Name:

Hoang Luu

Affiliation:

H2Corporation