Relational Database Storage

Spin provides two interfaces for relational (SQL) databases:

  • A built-in SQLite Database, which is always available and requires no management on your part.
  • “Bring your own database” support for MySQL and PostgreSQL, where you host and manage the database outside of Spin.

This page covers the “bring your own database” scenario. See SQLite Storage for the built-in service.

Why do I need a Spin interface? Why can't I just use my language's database libraries?

The current version of the WebAssembly System Interface (WASI) doesn’t provide a sockets interface, so database libraries that depend on sockets can’t be built to Wasm. The Spin interface means Wasm modules can bypass this limitation by asking Spin to make the database connection on their behalf.

Using MySQL and PostgreSQL From Applications

The Spin SDK surfaces the Spin MySQL and PostgreSQL interfaces to your language. The set of operations is the same across both databases:

openaddressconnection resourceOpens a connection to the specified database. The host must be listed in allowed_outbound_hosts. Other operations must be called through a connection.
querystatement, SQL parametersdatabase recordsRuns the specified statement against the database, returning the query results as a set of rows.
executestatement, SQL parametersinteger (not MySQL)Runs the specified statement against the database, returning the number of rows modified by the statement. (MySQL does not return the modified row count.)

The exact detail of calling these operations from your application depends on your language:

Want to go straight to the reference documentation? Find it here.

MySQL functions are available in the spin_sdk::mysql module, and PostgreSQL functions in the spin_sdk::pg module. The function names match the operations above. This example shows MySQL:

use spin_sdk::mysql::{self, Connection, Decode, ParameterValue};

let connection = Connection::open(&address)?;

let params = vec![ParameterValue::Int32(id)];
let rowset = connection.query("SELECT id, name FROM pets WHERE id = ?", &params)?;

match rowset.rows.first() {
    None => /* no rows matched query */,
    Some(row) => {
        let name = String::decode(&row[1])?;


  • Parameters are instances of the ParameterValue enum; you must wrap raw values in this type.
  • A row is a vector of the DbValue enum. Use the Decode trait to access conversions to common types.
  • Using PostgreSQL works in the same way, except that you use the spin_sdk::pg module instead of spin_sdk::mysql.
  • Modified row counts are returned as u64. (MySQL execute does not return the modified row count.)
  • All functions wrap the return in anyhow::Result.

You can find complete examples for using relational databases in the Spin repository on GitHub (MySQL, PostgreSQL).

For full information about the MySQL and PostgreSQL APIs, see the Spin SDK reference documentation.

Want to go straight to the reference documentation? Find it here.

The code below is an Outbound MySQL example. There is also an outbound PostgreSQL example available.

import { HandleRequest, HttpRequest, HttpResponse, Mysql } from "@fermyon/spin-sdk"

const encoder = new TextEncoder()

// Connects as the root user without a password 
const DB_URL = "mysql://root:@"

 Run the following commands to setup the instance:
 create database spin_dev;
 use spin_dev;
 create table test(id int, val int);
 insert into test values (4,4);

export const handleRequest: HandleRequest = async function (request: HttpRequest): Promise<HttpResponse> {

    Mysql.execute(DB_URL, "delete from test where id=?", [4])
    Mysql.execute(DB_URL, "insert into test values (4,5)", [])
    let test = Mysql.query(DB_URL, "select * from test", [])

    console.log(test.columns) (k => {

    return {
        status: 200,
        headers: {"foo": "bar"},
        body: encoder.encode("Hello from JS-SDK").buffer

The Python SDK doesn’t currently surface the MySQL or PostgreSQL APIs.

Want to go straight to the reference documentation? Find it here.

MySQL functions are available in the package, and PostgreSQL in See Go Packages for reference documentation.

The package follows the usual Go database API. Use Open to return a connection to the database of type *sql.DB - see the Go standard library documentation for usage information. For example:

package main

import (

	spinhttp ""

type Pet struct {
	ID        int64
	Name      string
	Prey      *string // nullable field must be a pointer
	IsFinicky bool

func init() {
	spinhttp.Handle(func(w http.ResponseWriter, r *http.Request) {

		// addr is the environment variable set in `spin.toml` that points to the
		// address of the Mysql server.
		addr := os.Getenv("DB_URL")

		db := pg.Open(addr)
		defer db.Close()

		_, err := db.Query("INSERT INTO pets VALUES ($1, 'Maya', $2, $3);", int32(4), "bananas", true)
		if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)

		rows, err := db.Query("SELECT * FROM pets")
		if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)

		var pets []*Pet
		for rows.Next() {
			var pet Pet
			if err := rows.Scan(&pet.ID, &pet.Name, &pet.Prey, &pet.IsFinicky); err != nil {
			pets = append(pets, &pet)

func main() {}

Granting Network Permissions to Components

By default, Spin components are not allowed to make outgoing network requests, including MySQL or PostgreSQL. This follows the general Wasm rule that modules must be explicitly granted capabilities, which is important to sandboxing. To grant a component permission to make network requests to a particular host, use the allowed_outbound_hosts field in the component manifest, specifying the host and allowed port:

allowed_outbound_hosts = ["postgres://"]