go-sql-spanner

Google Cloud Spanner driver for Go's database/sql package.

This driver can be used with both Spanner GoogleSQL and Spanner PostgreSQL databases.

import _ "github.com/googleapis/go-sql-spanner"

db, err := sql.Open("spanner", "projects/PROJECT/instances/INSTANCE/databases/DATABASE")
if err != nil {
    log.Fatal(err)
}

// Print singers with more than 500 likes.
rows, err := db.QueryContext(ctx, "SELECT id, name FROM singers WHERE likes > ?", 500)
if err != nil {
    log.Fatal(err)
}
defer rows.Close()

var (
    id   int64
    text string
)
for rows.Next() {
    if err := rows.Scan(&id, &text); err != nil {
        log.Fatal(err)
    }
    fmt.Println(id, text)
}

Statements

Statements support follows the official Google Cloud Spanner Go client style arguments as well as positional parameters. It is highly recommended to use either positional parameters in combination with positional arguments, or named parameters in combination with named arguments.

Using positional parameters with positional arguments

db.QueryContext(ctx, "SELECT id, text FROM tweets WHERE likes > ?", 500)

db.ExecContext(ctx, "INSERT INTO tweets (id, text, rts) VALUES (?, ?, ?)", id, text, 10000)

Using named parameters with named arguments

db.ExecContext(ctx, "DELETE FROM tweets WHERE id = @id", sql.Named("id", 14544498215374))

db.ExecContext(ctx, "INSERT INTO tweets (id, text, rts) VALUES (@id, @text, @rts)",
	sql.Named("id", id), sql.Named("text", text), sql.Named("rts", 10000))

Using PostgreSQL-style positional arguments

When connected to a PostgreSQL-dialect Spanner database, you can also use PostgreSQL-style query parameters $1, $2, ..., $n. These query parameters are handled as positional parameters.

db.QueryContext(ctx, "SELECT id, text FROM tweets WHERE likes > $1", 500)

db.ExecContext(ctx, "INSERT INTO tweets (id, text, rts) VALUES ($1, $2, $3)", id, text, 10000)

Using named parameters with positional arguments (not recommended)

Named parameters can also be used in combination with positional arguments, but this is not recommended, as the behavior can be hard to predict if the same named query parameter is used in multiple places in the statement.

// Possible, but not recommended.
db.ExecContext(ctx, "DELETE FROM tweets WHERE id = @id", 14544498215374)

Query Options

Query options can be passed in as arguments to a query. Pass in a value of type spannerdriver.ExecOptions to supply additional execution options for a statement. The spanner.QueryOptions will be passed through to the Spanner client as the query options to use for the query or DML statement.

tx.ExecContext(ctx, "INSERT INTO Singers (SingerId, Name) VALUES (@id, @name)",
	spannerdriver.ExecOptions{QueryOptions: spanner.QueryOptions{RequestTag: "insert_singer"}},
    123, "Bruce Allison")
tx.QueryContext(ctx, "SELECT SingerId, Name FROM Singers WHERE SingerId = ?",
    spannerdriver.ExecOptions{QueryOptions: spanner.QueryOptions{RequestTag: "select_singer"}},
    123)

Statement tags (request tags) can also be set using the custom SQL statement set statement_tag='my_tag':

tx.ExecContext(ctx, "set statement_tag = 'select_singer'")
tx.QueryContext(ctx, "SELECT SingerId, Name FROM Singers WHERE SingerId = ?", 123)

Transactions

• Read-write transactions support isolation levels Serializable, Snapshot and RepeatableRead.
• Read-only transactions do strong-reads by default. Read-only transactions must be ended by calling either Commit or Rollback. Calling either of these methods will end the current read-only transaction.

tx, err := db.BeginTx(ctx, &sql.TxOptions{}) // Read-write transaction.

// Read-write transaction with a transaction tag.
conn, _ := db.Conn(ctx)
_, _ := conn.ExecContext(ctx, "SET TRANSACTION_TAG='my_transaction_tag'")
tx, err := conn.BeginTx(ctx, &sql.TxOptions{})


tx, err := db.BeginTx(ctx, &sql.TxOptions{
    ReadOnly: true, // Read-only transaction using strong reads.
})

conn, _ := db.Conn(ctx)
_, _ := conn.ExecContext(ctx, "SET READ_ONLY_STALENESS='EXACT_STALENESS 10s'")
tx, err := conn.BeginTx(ctx, &sql.TxOptions{
    ReadOnly: true, // Read-only transaction using a 10 second exact staleness.
})

Transaction Runner (Retry Transactions)

Spanner can abort a read/write transaction if concurrent modifications are detected that would violate the transaction consistency. When this happens, the driver will return the ErrAbortedDueToConcurrentModification error. You can use the RunTransaction and RunTransactionWithOptions functions to let the driver automatically retry transactions that are aborted by Spanner.

package sample

import (
  "context"
  "database/sql"
  "fmt"

  _ "github.com/googleapis/go-sql-spanner"
  spannerdriver "github.com/googleapis/go-sql-spanner"
)

spannerdriver.RunTransactionWithOptions(ctx, db, &sql.TxOptions{}, func(ctx context.Context, tx *sql.Tx) error {
    row := tx.QueryRowContext(ctx, "select Name from Singers where SingerId=@id", 123)
    var name string
    if err := row.Scan(&name); err != nil {
        return err
    }
    return nil
}, spanner.TransactionOptions{TransactionTag: "my_transaction_tag"})

See also the transaction runner sample.

DDL Statements

DDL statements are not supported in transactions per Cloud Spanner restriction. Instead, run them on a connection without an active transaction:

db.ExecContext(ctx, "CREATE TABLE ...")

Multiple DDL statements can be sent in one batch to Cloud Spanner by defining a DDL batch:

conn, _ := db.Conn(ctx)
_, _ := conn.ExecContext(ctx, "START BATCH DDL")
_, _ = conn.ExecContext(ctx, "CREATE TABLE Singers (SingerId INT64, Name STRING(MAX)) PRIMARY KEY (SingerId)")
_, _ = conn.ExecContext(ctx, "CREATE INDEX Idx_Singers_Name ON Singers (Name)")
// Executing `RUN BATCH` will run the previous DDL statements as one batch.
_, _ := conn.ExecContext(ctx, "RUN BATCH")

See also the batch DDL example.

Examples

The examples directory contains standalone code samples that show how to use common features of Cloud Spanner and/or the database/sql package. Each standalone code sample can be executed without any prior setup, as long as Docker is installed on your local system.

Raw Connection / Specific Cloud Spanner Features

Use the Conn.Raw method to get access to a Cloud Spanner specific connection instance. This instance can be used to access Cloud Spanner specific features and settings, such as mutations, read-only staleness settings and commit timestamps.

conn, _ := db.Conn(ctx)
_ = conn.Raw(func(driverConn interface{}) error {
    spannerConn, ok := driverConn.(spannerdriver.SpannerConn)
    if !ok {
        return fmt.Errorf("unexpected driver connection %v, expected SpannerConn", driverConn)
    }
    // Use the `SpannerConn` interface to set specific Cloud Spanner settings or access
    // specific Cloud Spanner features.

    // Example: Set and get the current read-only staleness of the connection.
    _ = spannerConn.SetReadOnlyStaleness(spanner.ExactStaleness(10 * time.Second))
    _ = spannerConn.ReadOnlyStaleness()

    return nil
})

See also the examples directory for further code samples.

Emulator

See Google Cloud Spanner Emulator to learn how to start the emulator. Once the emulator is started and the host environmental flag is set, the driver will automatically connect to the emulator.

$ gcloud beta emulators spanner start
$ export SPANNER_EMULATOR_HOST=localhost:9010

Automatically Create Instance and Database on the Emulator

You can also add the autoConfigEmulator=true option to the connection string. This will instruct the driver to connect to the Spanner emulator, and to automatically create the Spanner instance and database on the emulator. See examples/emulator for a working example.

Spanner PostgreSQL Interface

This driver works with both Spanner GoogleSQL and PostgreSQL dialects. The driver automatically detects the dialect of the database that it is connected to.

Note that the types of query parameters that are supported depends on the dialect of the database that the driver is connected to:

1. Positional parameters (?): Supported for both dialects.
2. Named parameters (@id, @name, ...): Supported for both dialects.
3. PostgreSQL-style positional parameters ($1, $2, ...): Only supported for PostgreSQL databases.

Alternatives

You can also use Spanner PostgreSQL dialect databases with any off-the-shelf PostgreSQL driver that implements the database/sql interface in combination with PGAdapter.

For example, the pgx driver can be used in combination with PGAdapter: https://github.com/GoogleCloudPlatform/pgadapter/blob/postgresql-dialect/docs/pgx.md

Troubleshooting

The driver will retry any Aborted error that is returned by Cloud Spanner during a read/write transaction. If the driver detects that the data that was used by the transaction was changed by another transaction between the initial attempt and the retry attempt, the Aborted error will be propagated to the client application as an spannerdriver.ErrAbortedDueToConcurrentModification error.

Go Versions Supported

The Spanner database/sql driver follows the Go release policy and supports the two latest major Go versions.

Authorization

By default, each API will use Google Application Default Credentials for authorization credentials used in calling the API endpoints. This will allow your application to run in many environments without requiring explicit configuration.

Contributing

Contributions are welcome. Please, see the CONTRIBUTING document for details.

Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms. See Contributor Code of Conduct for more information.