SQLite-backed Durable Object Storage

Note

This page documents the storage API for the newer SQLite-backed Durable Objects.

For the legacy KV-backed Durable Object storage API, refer to KV-backed Durable Object Storage (Legacy).

The Durable Object Storage API allows Durable Objects to access transactional and strongly consistent storage. A Durable Object's attached storage is private to its unique instance and cannot be accessed by other objects.

The Durable Object Storage API comes with several methods, including SQL, point-in-time recovery (PITR), key-value (KV), and alarm APIs. Available API methods depend on the storage backend for a Durable Objects class, either SQLite or KV.

Methods 1	SQLite-backed Durable Object class	KV-backed Durable Object class
SQL API	✅	❌
PITR API	✅	❌
Synchronous KV API	✅ 2, 3	❌
Asynchronous KV API	✅ 3	✅
Alarms API	✅	✅

Footnotes

¹ Each method is implicitly wrapped inside a transaction, such that its results are atomic and isolated from all other storage operations, even when accessing multiple key-value pairs.

² KV API methods like get(), put(), delete(), or list() store data in a hidden SQLite table __cf_kv. Note that you will be able to view this table when listing all tables, but you will not be able to access its content through the SQL API.

³ SQLite-backed Durable Objects also use synchronous KV API methods using ctx.storage.kv, whereas KV-backed Durable Objects only provide asynchronous KV API methods.

Recommended SQLite-backed Durable Objects

Cloudflare recommends all new Durable Object namespaces use the SQLite storage backend. These Durable Objects can continue to use storage key-value API.

Additionally, SQLite-backed Durable Objects allow you to store more types of data (such as tables), and offer Point In Time Recovery API which can restore a Durable Object's embedded SQLite database contents (both SQL data and key-value data) to any point in the past 30 days.

The key-value storage backend remains for backwards compatibility, and a migration path from KV storage backend to SQLite storage backend for existing Durable Object namespaces will be available in the future.

Storage billing on SQLite-backed Durable Objects

Storage billing is not yet enabled for Durable Object classes using the SQLite storage backend. SQLite-backed Durable Objects will incur charges for requests and duration. Storage billing for SQLite-backed Durable Objects will be enabled at a later date with advance notice with the shared pricing.

Access storage

Durable Objects gain access to Storage API via the DurableObjectStorage interface and accessed by the DurableObjectState::storage property. This is frequently accessed via this.ctx.storage with the ctx parameter passed to the Durable Object constructor.

The following code snippet shows you how to store and retrieve data using the Durable Object Storage API.

JavaScript

JavaScript

export class Counter extends DurableObject {
  constructor(ctx, env) {
    super(ctx, env);
  }

  async increment() {
    let value = (await this.ctx.storage.get("value")) || 0;
    value += 1;
    await this.ctx.storage.put("value", value);
    return value;
  }
}

TypeScript

TypeScript

export class Counter extends DurableObject {
  constructor(ctx: DurableObjectState, env: Env) {
    super(ctx, env);
  }

    async increment(): Promise<number> {
      let value: number = (await this.ctx.storage.get('value')) || 0;
      value += 1;
      await this.ctx.storage.put('value', value);
      return value;
    }

}

JavaScript is a single-threaded and event-driven programming language. This means that JavaScript runtimes, by default, allow requests to interleave with each other which can lead to concurrency bugs. The Durable Objects runtime uses a combination of input gates and output gates to avoid this type of concurrency bug when performing storage operations. Learn more in our blog post ↗.

SQL API

The SqlStorage interface encapsulates methods that modify the SQLite database embedded within a Durable Object. The SqlStorage interface is accessible via the sql property of DurableObjectStorage class.

For example, using sql.exec() a user can create a table and insert rows.

TypeScript

import { DurableObject } from "cloudflare:workers";

export class MyDurableObject extends DurableObject {
  sql: SqlStorage;
  constructor(ctx: DurableObjectState, env: Env) {
    super(ctx, env);
    this.sql = ctx.storage.sql;

    this.sql.exec(`
      CREATE TABLE IF NOT EXISTS artist(
        artistid    INTEGER PRIMARY KEY,
        artistname  TEXT
      );
      INSERT INTO artist (artistid, artistname) VALUES
        (123, 'Alice'),
        (456, 'Bob'),
        (789, 'Charlie');
    `);
  }
}

• SQL API methods accessed with ctx.storage.sql are only allowed on Durable Object classes with SQLite storage backend and will return an error if called on Durable Object classes with a KV-storage backend.
• When writing data, every row update of an index counts as an additional row. However, indexes may be beneficial for read-heavy use cases. Refer to Index for SQLite Durable Objects.
• Writing data to SQLite virtual tables ↗ also counts towards rows written.

Durable Objects support a subset of SQLite extensions for added functionality, including:

• FTS5 module ↗ for full-text search (including fts5vocab).
• JSON extension ↗ for JSON functions and operators.
• Math functions ↗.

Refer to the source code ↗ for the full list of supported functions.

exec

exec(query: string, ...bindings: any[]): SqlStorageCursor

Parameters

• query: string
  • The SQL query string to be executed. query can contain ? placeholders for parameter bindings. Multiple SQL statements, separated with a semicolon, can be executed in the query. With multiple SQL statements, any parameter bindings are applied to the last SQL statement in the query, and the returned cursor is only for the last SQL statement.
• ...bindings: any[] Optional
  • Optional variable number of arguments that correspond to the ? placeholders in query.

Returns

A cursor (SqlStorageCursor) to iterate over query row results as objects. SqlStorageCursor is a JavaScript Iterable ↗, which supports iteration using for (let row of cursor). SqlStorageCursor is also a JavaScript Iterator ↗, which supports iteration using cursor.next().

SqlStorageCursor supports the following methods:

• next()
  • Returns an object representing the next value of the cursor. The returned object has done and value properties adhering to the JavaScript Iterator ↗. done is set to false when a next value is present, and value is set to the next row object in the query result. done is set to true when the entire cursor is consumed, and no value is set.
• toArray()
  • Iterates through remaining cursor value(s) and returns an array of returned row objects.
• one()
  • Returns a row object if query result has exactly one row. If query result has zero rows or more than one row, one() throws an exception.
• raw(): Iterator
  • Returns an Iterator over the same query results, with each row as an array of column values (with no column names) rather than an object.
  • Returned Iterator supports next() and toArray() methods above.
  • Returned cursor and raw() iterator iterate over the same query results and can be combined. For example:

TypeScript

let cursor = this.sql.exec("SELECT * FROM artist ORDER BY artistname ASC;");
let rawResult = cursor.raw().next();

if (!rawResult.done) {
  console.log(rawResult.value); // prints [ 123, 'Alice' ]
} else {
  // query returned zero results
}

console.log(cursor.toArray()); // prints [{ artistid: 456, artistname: 'Bob' },{ artistid: 789, artistname: 'Charlie' }]

SqlStorageCursor has the following properties:

• columnNames: string[]
  • The column names of the query in the order they appear in each row array returned by the raw iterator.
• rowsRead: number
  • The number of rows read so far as part of this SQL query. This may increase as you iterate the cursor. The final value is used for SQL billing.
• rowsWritten: number
  • The number of rows written so far as part of this SQL query. This may increase as you iterate the cursor. The final value is used for SQL billing.
• Any numeric value in a column is affected by JavaScript's 52-bit precision for numbers. If you store a very large number (in int64), then retrieve the same value, the returned value may be less precise than your original number.

SQL transactions

Note that sql.exec() cannot execute transaction-related statements like BEGIN TRANSACTION or SAVEPOINT. Instead, use the ctx.storage.transaction() or ctx.storage.transactionSync() APIs to start a transaction, and then execute SQL queries in your callback.

Examples

SQL API examples below use the following SQL schema:

TypeScript

import { DurableObject } from "cloudflare:workers";

export class MyDurableObject extends DurableObject {
  sql: SqlStorage
  constructor(ctx: DurableObjectState, env: Env) {
    super(ctx, env);
    this.sql = ctx.storage.sql;

    this.sql.exec(`CREATE TABLE IF NOT EXISTS artist(
      artistid    INTEGER PRIMARY KEY,
      artistname  TEXT
    );INSERT INTO artist (artistid, artistname) VALUES
      (123, 'Alice'),
      (456, 'Bob'),
      (789, 'Charlie');`
    );
  }
}

Iterate over query results as row objects:

TypeScript

  let cursor = this.sql.exec("SELECT * FROM artist;");

  for (let row of cursor) {
    // Iterate over row object and do something
  }

Convert query results to an array of row objects:

TypeScript

  // Return array of row objects: [{"artistid":123,"artistname":"Alice"},{"artistid":456,"artistname":"Bob"},{"artistid":789,"artistname":"Charlie"}]
  let resultsArray1 = this.sql.exec("SELECT * FROM artist;").toArray();
  // OR
  let resultsArray2 = Array.from(this.sql.exec("SELECT * FROM artist;"));
  // OR
  let resultsArray3 = [...this.sql.exec("SELECT * FROM artist;")]; // JavaScript spread syntax

Convert query results to an array of row values arrays:

TypeScript

  // Returns [[123,"Alice"],[456,"Bob"],[789,"Charlie"]]
  let cursor = this.sql.exec("SELECT * FROM artist;");
  let resultsArray = cursor.raw().toArray();

  // Returns ["artistid","artistname"]
  let columnNameArray = this.sql.exec("SELECT * FROM artist;").columnNames.toArray();

Get first row object of query results:

TypeScript

  // Returns {"artistid":123,"artistname":"Alice"}
  let firstRow = this.sql.exec("SELECT * FROM artist ORDER BY artistname DESC;").toArray()[0];

Check if query results have exactly one row:

TypeScript

  // returns error
  this.sql.exec("SELECT * FROM artist ORDER BY artistname ASC;").one();

  // returns { artistid: 123, artistname: 'Alice' }
  let oneRow = this.sql.exec("SELECT * FROM artist WHERE artistname = ?;", "Alice").one()

Returned cursor behavior:

TypeScript

  let cursor = this.sql.exec("SELECT * FROM artist ORDER BY artistname ASC;");
  let result = cursor.next();
  if (!result.done) {
    console.log(result.value); // prints { artistid: 123, artistname: 'Alice' }
  } else {
    // query returned zero results
  }

  let remainingRows = cursor.toArray();
  console.log(remainingRows); // prints [{ artistid: 456, artistname: 'Bob' },{ artistid: 789, artistname: 'Charlie' }]

Returned cursor and raw() iterator iterate over the same query results:

TypeScript

  let cursor = this.sql.exec("SELECT * FROM artist ORDER BY artistname ASC;");
  let result = cursor.raw().next();

  if (!result.done) {
    console.log(result.value); // prints [ 123, 'Alice' ]
  } else {
    // query returned zero results
  }

  console.log(cursor.toArray()); // prints [{ artistid: 456, artistname: 'Bob' },{ artistid: 789, artistname: 'Charlie' }]

sql.exec().rowsRead():

TypeScript

  let cursor = this.sql.exec("SELECT * FROM artist;");
  cursor.next()
  console.log(cursor.rowsRead); // prints 1

  cursor.toArray(); // consumes remaining cursor
  console.log(cursor.rowsRead); // prints 3

databaseSize

databaseSize: number

Returns

The current SQLite database size in bytes.

TypeScript

let size = ctx.storage.sql.databaseSize;

PITR (Point In Time Recovery) API

For SQLite-backed Durable Objects, the following point-in-time-recovery (PITR) API methods are available to restore a Durable Object's embedded SQLite database to any point in time in the past 30 days. These methods apply to the entire SQLite database contents, including both the object's stored SQL data and stored key-value data using the key-value put() API. The PITR API is not supported in local development because a durable log of data changes is not stored locally.

The PITR API represents points in time using 'bookmarks'. A bookmark is a mostly alphanumeric string like 0000007b-0000b26e-00001538-0c3e87bb37b3db5cc52eedb93cd3b96b. Bookmarks are designed to be lexically comparable: a bookmark representing an earlier point in time compares less than one representing a later point, using regular string comparison.

getCurrentBookmark

ctx.storage.getCurrentBookmark(): Promise<string>

• Returns a bookmark representing the current point in time in the object's history.

getBookmarkForTime

ctx.storage.getBookmarkForTime(timestamp: number | Date): Promise<string>

• Returns a bookmark representing approximately the given point in time, which must be within the last 30 days. If the timestamp is represented as a number, it is converted to a date as if using new Date(timestamp).

onNextSessionRestoreBookmark

ctx.storage.onNextSessionRestoreBookmark(bookmark: string): Promise<string>

• Configures the Durable Object so that the next time it restarts, it should restore its storage to exactly match what the storage contained at the given bookmark. After calling this, the application should typically invoke ctx.abort() to restart the Durable Object, thus completing the point-in-time recovery.

This method returns a special bookmark representing the point in time immediately before the recovery takes place (even though that point in time is still technically in the future). Thus, after the recovery completes, it can be undone by performing a second recovery to this bookmark.

TypeScript

let now = new Date();
// restore to 2 days ago
let bookmark = ctx.storage.getBookmarkForTime(now - 2);
ctx.storage.onNextSessionRestoreBookmark(bookmark);

Synchronous KV API

get

• ctx.storage.kv.get(key string): Any, undefined
  • Retrieves the value associated with the given key. The type of the returned value will be whatever was previously written for the key, or undefined if the key does not exist.

put

• ctx.storage.kv.put(key string, value any): void

  • Stores the value and associates it with the given key. The value can be any type supported by the structured clone algorithm ↗, which is true of most types.

    For the size of keys and values refer to SQLite-backed Durable Object limits

delete

• ctx.storage.kv.delete(key string): boolean
  • Deletes the key and associated value. Returns true if the key existed or false if it did not.

list

• ctx.storage.kv.list(options Object optional): Iterable<string, any>

  • Returns all keys and values associated with the current Durable Object in ascending sorted order based on the keys' UTF-8 encodings.

  • The type of each returned value in the Iterable ↗ will be whatever was previously written for the corresponding key.

  • Be aware of how much data may be stored in your Durable Object before calling this version of list without options because all the data will be loaded into the Durable Object's memory, potentially hitting its limit. If that is a concern, pass options to list as documented below.

Supported options

• start string

  • Key at which the list results should start, inclusive.

• startAfter string

  • Key after which the list results should start, exclusive. Cannot be used simultaneously with start.

• end string

  • Key at which the list results should end, exclusive.

• prefix string

  • Restricts results to only include key-value pairs whose keys begin with the prefix.

• reverse boolean

  • If true, return results in descending order instead of the default ascending order.
  • Enabling reverse does not change the meaning of start, startKey, or endKey. start still defines the smallest key in lexicographic order that can be returned (inclusive), effectively serving as the endpoint for a reverse-order list. end still defines the largest key in lexicographic order that the list should consider (exclusive), effectively serving as the starting point for a reverse-order list.

• limit number

  • Maximum number of key-value pairs to return.

Alarms

getAlarm

• getAlarm(options Object optional): Promise<Number | null>
  • Retrieves the current alarm time (if set) as integer milliseconds since epoch. The alarm is considered to be set if it has not started, or if it has failed and any retry has not begun. If no alarm is set, getAlarm() returns null.

Supported options

• Same options as get(), but without noCache.

setAlarm

• setAlarm(scheduledTime Date | number, options Object optional): Promise

  • Sets the current alarm time, accepting either a JavaScript Date, or integer milliseconds since epoch.

  If setAlarm() is called with a time equal to or before Date.now(), the alarm will be scheduled for asynchronous execution in the immediate future. If the alarm handler is currently executing in this case, it will not be canceled. Alarms can be set to millisecond granularity and will usually execute within a few milliseconds after the set time, but can be delayed by up to a minute due to maintenance or failures while failover takes place.

deleteAlarm

• deleteAlarm(options Object optional): Promise
  • Deletes the alarm if one exists. Does not cancel the alarm handler if it is currently executing.

Supported options

• setAlarm() and deleteAlarm() support the same options as put(), but without noCache.

Other

deleteAll

• deleteAll(options Object optional): Promise
  • Deletes all stored data, effectively deallocating all storage used by the Durable Object. For Durable Objects with a key-value storage backend, deleteAll() removes all keys and associated values for an individual Durable Object. For Durable Objects with a SQLite storage backend, deleteAll() removes the entire contents of a Durable Object's private SQLite database, including both SQL data and key-value data.
  • For Durable Objects with a key-value storage backend, an in-progress deleteAll() operation can fail, which may leave a subset of data undeleted. Durable Objects with a SQLite storage backend do not have a partial deleteAll() issue because deleteAll() operations are atomic (all or nothing).
  • deleteAll() does not proactively delete alarms. Use deleteAlarm() to delete an alarm.

transactionSync

• transactionSync(callback): any

  • Only available when using SQLite-backed Durable Objects.

  • Invokes callback() wrapped in a transaction, and returns its result.

  • If callback() throws an exception, the transaction will be rolled back.

  • The callback must complete synchronously, that is, it should not be declared async nor otherwise return a Promise. Only synchronous storage operations can be part of the transaction. This is intended for use with SQL queries using ctx.storage.sql.exec(), which complete sychronously.

transaction

• transaction(closureFunction(txn)): Promise

  • Runs the sequence of storage operations called on txn in a single transaction that either commits successfully or aborts.

  • Explicit transactions are no longer necessary. Any series of write operations with no intervening await will automatically be submitted atomically, and the system will prevent concurrent events from executing while await a read operation (unless you use allowConcurrency: true). Therefore, a series of reads followed by a series of writes (with no other intervening I/O) are automatically atomic and behave like a transaction.

• txn

  • Provides access to the put(), get(), delete(), and list() methods documented above to run in the current transaction context. In order to get transactional behavior within a transaction closure, you must call the methods on the txn Object instead of on the top-level ctx.storage Object.
    
    Also supports a rollback() function that ensures any changes made during the transaction will be rolled back rather than committed. After rollback() is called, any subsequent operations on the txn Object will fail with an exception. rollback() takes no parameters and returns nothing to the caller.

  • When using the SQLite-backed storage engine, the txn object is obsolete. Any storage operations performed directly on the ctx.storage object, including SQL queries using ctx.storage.sql.exec(), will be considered part of the transaction.

sync

• sync(): Promise

  • Synchronizes any pending writes to disk.

  • This is similar to normal behavior from automatic write coalescing. If there are any pending writes in the write buffer (including those submitted with the allowUnconfirmed option), the returned promise will resolve when they complete. If there are no pending writes, the returned promise will be already resolved.

Storage properties

sql

sql is a readonly property of type DurableObjectStorage encapsulating the SQL API.

Related resources

• Durable Objects: Easy, Fast, Correct Choose Three ↗
• Zero-latency SQLite storage in every Durable Object blog ↗
• WebSockets API