This tutorial shows you how build a simple Go application with CockroachDB and the Go pq driver.
Before you begin
- Install CockroachDB.
- Start up a secure or insecure local cluster.
- Choose the instructions that correspond to whether your cluster is secure or insecure:
Step 1. Install the Go pq driver
To install the Go pq driver, run the following command:
$ go get -u github.com/lib/pq
Step 2. Create the maxroach user and bank database
Start the built-in SQL shell:
$ cockroach sql --certs-dir=certs
In the SQL shell, issue the following statements to create the maxroach user and bank database:
> CREATE USER IF NOT EXISTS maxroach;
> CREATE DATABASE bank;
Give the maxroach user the necessary permissions:
> GRANT ALL ON DATABASE bank TO maxroach;
Exit the SQL shell:
> \q
Step 3. Generate a certificate for the maxroach user
Create a certificate and key for the maxroach user by running the following command:
$ cockroach cert create-client maxroach --certs-dir=certs --ca-key=my-safe-directory/ca.key
The code samples will run with maxroach as the user.
Step 4. Run the Go 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.
To clone a version of the code below that connects to insecure clusters, run the following:
git clone https://github.com/cockroachlabs/hello-world-go-pq/
Note that you will need to edit the connection string to use the certificates that you generated when you set up your secure cluster.
Basic statements
First, use the following code to connect as the maxroach user and execute some basic SQL statements, creating a table, inserting rows, and reading and printing the rows.
Download the basic-sample.go file, or create the file yourself and copy the code into it.
package main
import (
"database/sql"
"fmt"
"log"
_ "github.com/lib/pq"
)
func main() {
// Connect to the "bank" database.
db, err := sql.Open("postgres",
"postgresql://maxroach@localhost:26257/bank?ssl=true&sslmode=require&sslrootcert=certs/ca.crt&sslkey=certs/client.maxroach.key&sslcert=certs/client.maxroach.crt")
if err != nil {
log.Fatal("error connecting to the database: ", err)
}
defer db.Close()
// Create the "accounts" table.
if _, err := db.Exec(
"CREATE TABLE IF NOT EXISTS accounts (id INT PRIMARY KEY, balance INT)"); err != nil {
log.Fatal(err)
}
// Insert two rows into the "accounts" table.
if _, err := db.Exec(
"INSERT INTO accounts (id, balance) VALUES (1, 1000), (2, 250)"); err != nil {
log.Fatal(err)
}
// Print out the balances.
rows, err := db.Query("SELECT id, balance FROM accounts")
if err != nil {
log.Fatal(err)
}
defer rows.Close()
fmt.Println("Initial balances:")
for rows.Next() {
var id, balance int
if err := rows.Scan(&id, &balance); err != nil {
log.Fatal(err)
}
fmt.Printf("%d %d\n", id, balance)
}
}
Then run the code:
$ go run basic-sample.go
The output should be:
Initial balances:
1 1000
2 250
Transaction (with retry logic)
Next, use the following code to again connect as the maxroach user but this time will 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.go file, or create the file yourself and copy the code into it.
package main
import (
"context"
"database/sql"
"fmt"
"log"
"github.com/cockroachdb/cockroach-go/crdb"
)
func transferFunds(tx *sql.Tx, from int, to int, amount int) error {
// Read the balance.
var fromBalance int
if err := tx.QueryRow(
"SELECT balance FROM accounts WHERE id = $1", from).Scan(&fromBalance); err != nil {
return err
}
if fromBalance < amount {
return fmt.Errorf("insufficient funds")
}
// Perform the transfer.
if _, err := tx.Exec(
"UPDATE accounts SET balance = balance - $1 WHERE id = $2", amount, from); err != nil {
return err
}
if _, err := tx.Exec(
"UPDATE accounts SET balance = balance + $1 WHERE id = $2", amount, to); err != nil {
return err
}
return nil
}
func main() {
db, err := sql.Open("postgres",
"postgresql://maxroach@localhost:26257/bank?ssl=true&sslmode=require&sslrootcert=certs/ca.crt&sslkey=certs/client.maxroach.key&sslcert=certs/client.maxroach.crt")
if err != nil {
log.Fatal("error connecting to the database: ", err)
}
defer db.Close()
// Run a transfer in a transaction.
err = crdb.ExecuteTx(context.Background(), db, nil, func(tx *sql.Tx) error {
return transferFunds(tx, 1 /* from acct# */, 2 /* to acct# */, 100 /* amount */)
})
if err == nil {
fmt.Println("Success")
} else {
log.Fatal("error: ", err)
}
}
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. For Go, the CockroachDB retry function is in the crdb package of the CockroachDB Go client. To install, clone the library into your $GOPATH as follows:
$ mkdir -p $GOPATH/src/github.com/cockroachdb
$ cd $GOPATH/src/github.com/cockroachdb
$ git clone git@github.com:cockroachdb/cockroach-go.git
Then run the code:
$ go run txn-sample.go
The output should be:
Success
To verify that funds were transferred from one account to another, use the built-in SQL client:
$ cockroach sql --certs-dir=certs -e 'SELECT id, balance FROM accounts' --database=bank
id | balance
-----+----------
1 | 900
2 | 350
(2 rows)
Step 2. Create the maxroach user and bank database
Start the built-in SQL shell:
$ cockroach sql --insecure
In the SQL shell, issue the following statements to create the maxroach user and bank database:
> CREATE USER IF NOT EXISTS maxroach;
> CREATE DATABASE bank;
Give the maxroach user the necessary permissions:
> GRANT ALL ON DATABASE bank TO maxroach;
Exit the SQL shell:
> \q
Step 3. Run the Go 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.
To clone a version of the code below that connects to insecure clusters, run the following:
git clone https://github.com/cockroachlabs/hello-world-go-pq/
Note that you will need to edit the connection string to use the certificates that you generated when you set up your secure cluster.
Basic statements
First, use the following code to connect as the maxroach user and execute some basic SQL statements, creating a table, inserting rows, and reading and printing the rows.
Download the basic-sample.go file, or create the file yourself and copy the code into it.
package main
import (
"database/sql"
"fmt"
"log"
_ "github.com/lib/pq"
)
func main() {
// Connect to the "bank" database.
db, err := sql.Open("postgres", "postgresql://maxroach@localhost:26257/bank?sslmode=disable")
if err != nil {
log.Fatal("error connecting to the database: ", err)
}
// Create the "accounts" table.
if _, err := db.Exec(
"CREATE TABLE IF NOT EXISTS accounts (id INT PRIMARY KEY, balance INT)"); err != nil {
log.Fatal(err)
}
// Insert two rows into the "accounts" table.
if _, err := db.Exec(
"INSERT INTO accounts (id, balance) VALUES (1, 1000), (2, 250)"); err != nil {
log.Fatal(err)
}
// Print out the balances.
rows, err := db.Query("SELECT id, balance FROM accounts")
if err != nil {
log.Fatal(err)
}
defer rows.Close()
fmt.Println("Initial balances:")
for rows.Next() {
var id, balance int
if err := rows.Scan(&id, &balance); err != nil {
log.Fatal(err)
}
fmt.Printf("%d %d\n", id, balance)
}
}
Then run the code:
$ go run basic-sample.go
The output should be:
Initial balances:
1 1000
2 250
Transaction (with retry logic)
Next, use the following code to again connect as the maxroach user but this time will 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.go file, or create the file yourself and copy the code into it.
package main
import (
"context"
"database/sql"
"fmt"
"log"
"github.com/cockroachdb/cockroach-go/crdb"
)
func transferFunds(tx *sql.Tx, from int, to int, amount int) error {
// Read the balance.
var fromBalance int
if err := tx.QueryRow(
"SELECT balance FROM accounts WHERE id = $1", from).Scan(&fromBalance); err != nil {
return err
}
if fromBalance < amount {
return fmt.Errorf("insufficient funds")
}
// Perform the transfer.
if _, err := tx.Exec(
"UPDATE accounts SET balance = balance - $1 WHERE id = $2", amount, from); err != nil {
return err
}
if _, err := tx.Exec(
"UPDATE accounts SET balance = balance + $1 WHERE id = $2", amount, to); err != nil {
return err
}
return nil
}
func main() {
db, err := sql.Open("postgres", "postgresql://maxroach@localhost:26257/bank?sslmode=disable")
if err != nil {
log.Fatal("error connecting to the database: ", err)
}
// Run a transfer in a transaction.
err = crdb.ExecuteTx(context.Background(), db, nil, func(tx *sql.Tx) error {
return transferFunds(tx, 1 /* from acct# */, 2 /* to acct# */, 100 /* amount */)
})
if err == nil {
fmt.Println("Success")
} else {
log.Fatal("error: ", err)
}
}
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. For Go, the CockroachDB retry function is in the crdb package of the CockroachDB Go client.
To install the CockroachDB Go client, run the following command:
$ go get -d github.com/cockroachdb/cockroach-go
Then run the code:
$ go run txn-sample.go
The output should be:
Success
To verify that funds were transferred from one account to another, use the built-in SQL client:
$ 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 Go pq driver.
You might also be interested in the following pages:
- Client Connection Parameters
- Data Replication
- Fault Tolerance & Recovery
- Replication & Rebalancing
- Cross-Cloud Migration
- Automated Operations
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