This tutorial shows you how build a simple Rust application with CockroachDB and the Rust Postgres driver.

We have tested the Rust Postgres driver enough to claim beta-level support. If you encounter problems, please open an issue with details to help us make progress toward full support.

Before you begin

  1. Install CockroachDB.
  2. Start up a secure or insecure local cluster.
  3. Choose the instructions that correspond to whether your cluster is secure or insecure:

Step 1. Specify the Rust Postgres driver as a dependency

Update your Cargo.toml file to specify a dependency on the Rust Postgres driver, as described in the official documentation.

Additionally, include the OpenSSL bindings and Rust Postgres OpenSSL crates as dependencies.

Step 2. Create the maxroach users and bank database

Start the built-in SQL shell:

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$ cockroach sql --certs-dir=certs

In the SQL shell, issue the following statements to create the maxroach user and bank database:

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> CREATE USER IF NOT EXISTS maxroach;
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> CREATE DATABASE bank;

Give the maxroach user the necessary permissions:

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> GRANT ALL ON DATABASE bank TO maxroach;

Exit the SQL shell:

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> \q

Step 3. Generate a certificate for the maxroach user

Create a certificate and key for the maxroach user by running the following command. The code samples will run as this user.

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$ cockroach cert create-client maxroach --certs-dir=certs --ca-key=my-safe-directory/ca.key

Step 4. Run the Rust code

Now that you have a database and a user, you'll run code to create a table and insert some rows, and then you'll run code to read and update values as an atomic transaction.

Basic statements

First, use the following code to connect as the maxroach user and execute some basic SQL statements, inserting rows and reading and printing the rows.

Download the basic-sample.rs file, or create the file yourself and copy the code into it.

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use openssl::error::ErrorStack;
use openssl::ssl::{SslConnector, SslFiletype, SslMethod};
use postgres::Client;
use postgres_openssl::MakeTlsConnector;

fn ssl_config() -> Result<MakeTlsConnector, ErrorStack> {
    let mut builder = SslConnector::builder(SslMethod::tls())?;
    builder.set_ca_file("certs/ca.crt")?;
    builder.set_certificate_chain_file("certs/client.maxroach.crt")?;
    builder.set_private_key_file("certs/client.maxroach.key", SslFiletype::PEM)?;
    Ok(MakeTlsConnector::new(builder.build()))
}

fn main() {
    let connector = ssl_config().unwrap();
    let mut client =
        Client::connect("postgresql://maxroach@localhost:26257/bank", connector).unwrap();

    // Create the "accounts" table.
    client
        .execute(
            "CREATE TABLE IF NOT EXISTS accounts (id INT PRIMARY KEY, balance INT)",
            &[],
        )
        .unwrap();

    // Insert two rows into the "accounts" table.
    client
        .execute(
            "INSERT INTO accounts (id, balance) VALUES (1, 1000), (2, 250)",
            &[],
        )
        .unwrap();

    // Print out the balances.
    println!("Initial balances:");
    for row in &client
        .query("SELECT id, balance FROM accounts", &[])
        .unwrap()
    {
        let id: i64 = row.get(0);
        let balance: i64 = row.get(1);
        println!("{} {}", id, balance);
    }
}

Transaction (with retry logic)

Next, use the following code to again connect as the maxroach user but this time execute a batch of statements as an atomic transaction to transfer funds from one account to another, where all included statements are either committed or aborted.

Download the txn-sample.rs file, or create the file yourself and copy the code into it.

Note:

CockroachDB may require the client to retry a transaction in case of read/write contention. CockroachDB provides a generic retry function that runs inside a transaction and retries it as needed. You can copy and paste the retry function from here into your code.

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use openssl::error::ErrorStack;
use openssl::ssl::{SslConnector, SslFiletype, SslMethod};
use postgres::{error::SqlState, Client, Error, Transaction};
use postgres_openssl::MakeTlsConnector;

/// Runs op inside a transaction and retries it as needed.
/// On non-retryable failures, the transaction is aborted and
/// rolled back; on success, the transaction is committed.
fn execute_txn<T, F>(client: &mut Client, op: F) -> Result<T, Error>
where
    F: Fn(&mut Transaction) -> Result<T, Error>,
{
    let mut txn = client.transaction()?;
    loop {
        let mut sp = txn.savepoint("cockroach_restart")?;
        match op(&mut sp).and_then(|t| sp.commit().map(|_| t)) {
            Err(ref err)
                if err
                    .code()
                    .map(|e| *e == SqlState::T_R_SERIALIZATION_FAILURE)
                    .unwrap_or(false) => {}
            r => break r,
        }
    }
    .and_then(|t| txn.commit().map(|_| t))
}

fn transfer_funds(txn: &mut Transaction, from: i64, to: i64, amount: i64) -> Result<(), Error> {
    // Read the balance.
    let from_balance: i64 = txn
        .query_one("SELECT balance FROM accounts WHERE id = $1", &[&from])?
        .get(0);

    assert!(from_balance >= amount);

    // Perform the transfer.
    txn.execute(
        "UPDATE accounts SET balance = balance - $1 WHERE id = $2",
        &[&amount, &from],
    )?;
    txn.execute(
        "UPDATE accounts SET balance = balance + $1 WHERE id = $2",
        &[&amount, &to],
    )?;
    Ok(())
}

fn ssl_config() -> Result<MakeTlsConnector, ErrorStack> {
    let mut builder = SslConnector::builder(SslMethod::tls())?;
    builder.set_ca_file("certs/ca.crt")?;
    builder.set_certificate_chain_file("certs/client.maxroach.crt")?;
    builder.set_private_key_file("certs/client.maxroach.key", SslFiletype::PEM)?;
    Ok(MakeTlsConnector::new(builder.build()))
}

fn main() {
    let connector = ssl_config().unwrap();
    let mut client =
        Client::connect("postgresql://maxroach@localhost:26257/bank", connector).unwrap();

    // Run a transfer in a transaction.
    execute_txn(&mut client, |txn| transfer_funds(txn, 1, 2, 100)).unwrap();

    // Check account balances after the transaction.
    for row in &client
        .query("SELECT id, balance FROM accounts", &[])
        .unwrap()
    {
        let id: i64 = row.get(0);
        let balance: i64 = row.get(1);
        println!("{} {}", id, balance);
    }
}

After running the code, use the built-in SQL client to verify that funds were transferred from one account to another:

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$ cockroach sql --certs-dir=certs -e 'SELECT id, balance FROM accounts' --database=bank
+----+---------+
| id | balance |
+----+---------+
|  1 |     900 |
|  2 |     350 |
+----+---------+
(2 rows)

Step 1. Specify the Rust Postgres driver as a dependency

Update your Cargo.toml file to specify a dependency on the Rust Postgres driver, as described in the official documentation.

Step 2. Create the maxroach users and bank database

Start the built-in SQL shell:

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$ cockroach sql --insecure

In the SQL shell, issue the following statements to create the maxroach user and bank database:

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> CREATE USER IF NOT EXISTS maxroach;
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> CREATE DATABASE bank;

Give the maxroach user the necessary permissions:

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> GRANT ALL ON DATABASE bank TO maxroach;

Exit the SQL shell:

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> \q

Step 3. Create a table in the new database

As the maxroach user, use the built-in SQL client to create an accounts table in the new database.

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$ cockroach sql --insecure \
--database=bank \
--user=maxroach \
-e 'CREATE TABLE accounts (id INT PRIMARY KEY, balance INT)'

Step 4. Run the Rust code

Now that you have a database and a user, you'll run code to create a table and insert some rows, and then you'll run code to read and update values as an atomic transaction.

Basic statements

First, use the following code to connect as the maxroach user and execute some basic SQL statements, inserting rows and reading and printing the rows.

Download the basic-sample.rs file, or create the file yourself and copy the code into it.

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use postgres::{Client, NoTls};

fn main() {
    let mut client = Client::connect("postgresql://maxroach@localhost:26257/bank", NoTls).unwrap();

    // Create the "accounts" table.
    client
        .execute(
            "CREATE TABLE IF NOT EXISTS accounts (id INT PRIMARY KEY, balance INT)",
            &[],
        )
        .unwrap();

    // Insert two rows into the "accounts" table.
    client
        .execute(
            "INSERT INTO accounts (id, balance) VALUES (1, 1000), (2, 250)",
            &[],
        )
        .unwrap();

    // Print out the balances.
    println!("Initial balances:");
    for row in &client
        .query("SELECT id, balance FROM accounts", &[])
        .unwrap()
    {
        let id: i64 = row.get(0);
        let balance: i64 = row.get(1);
        println!("{} {}", id, balance);
    }
}

Transaction (with retry logic)

Next, use the following code to again connect as the maxroach user but this time execute a batch of statements as an atomic transaction to transfer funds from one account to another, where all included statements are either committed or aborted.

Download the txn-sample.rs file, or create the file yourself and copy the code into it.

Note:

CockroachDB may require the client to retry a transaction in case of read/write contention. CockroachDB provides a generic retry function that runs inside a transaction and retries it as needed. You can copy and paste the retry function from here into your code.

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use postgres::{error::SqlState, Client, Error, NoTls, Transaction};

/// Runs op inside a transaction and retries it as needed.
/// On non-retryable failures, the transaction is aborted and
/// rolled back; on success, the transaction is committed.
fn execute_txn<T, F>(client: &mut Client, op: F) -> Result<T, Error>
where
    F: Fn(&mut Transaction) -> Result<T, Error>,
{
    let mut txn = client.transaction()?;
    loop {
        let mut sp = txn.savepoint("cockroach_restart")?;
        match op(&mut sp).and_then(|t| sp.commit().map(|_| t)) {
            Err(ref err)
                if err
                    .code()
                    .map(|e| *e == SqlState::T_R_SERIALIZATION_FAILURE)
                    .unwrap_or(false) => {}
            r => break r,
        }
    }
    .and_then(|t| txn.commit().map(|_| t))
}

fn transfer_funds(txn: &mut Transaction, from: i64, to: i64, amount: i64) -> Result<(), Error> {
    // Read the balance.
    let from_balance: i64 = txn
        .query_one("SELECT balance FROM accounts WHERE id = $1", &[&from])?
        .get(0);

    assert!(from_balance >= amount);

    // Perform the transfer.
    txn.execute(
        "UPDATE accounts SET balance = balance - $1 WHERE id = $2",
        &[&amount, &from],
    )?;
    txn.execute(
        "UPDATE accounts SET balance = balance + $1 WHERE id = $2",
        &[&amount, &to],
    )?;
    Ok(())
}

fn main() {
    let mut client = Client::connect("postgresql://maxroach@localhost:26257/bank", NoTls).unwrap();

    // Run a transfer in a transaction.
    execute_txn(&mut client, |txn| transfer_funds(txn, 1, 2, 100)).unwrap();

    // Check account balances after the transaction.
    for row in &client
        .query("SELECT id, balance FROM accounts", &[])
        .unwrap()
    {
        let id: i64 = row.get(0);
        let balance: i64 = row.get(1);
        println!("{} {}", id, balance);
    }
}

After running the code, use the built-in SQL client to verify that funds were transferred from one account to another:

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$ cockroach sql --insecure -e 'SELECT id, balance FROM accounts' --database=bank
+----+---------+
| id | balance |
+----+---------+
|  1 |     900 |
|  2 |     350 |
+----+---------+
(2 rows)

What's next?

Read more about using the Rust Postgres driver.

You might also be interested in the following pages:



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