go-sql-2pc

gosql2pc is a Golang library for implementing two phase commit transactions (2PC) in PostgreSQL, ensuring atomicity and consistency across distributed systems.

Features

• Provides a simple and easy-to-use API for managing two phase commit transactions in PostgreSQL.
• Supports distributed transaction management across multiple databases.
• Ensures atomicity and consistency of transactions using the two phase commit protocol.

Installation

To install go-sql-2pc, run the following command:

go get github.com/gosom/gosql2pc

Usage

package main

import (
	"context"
	"database/sql"

	twophase "github.com/gosom/gosql2pc"
	_ "github.com/jackc/pgx/stdlib"
)

func main() {
	// Connect to the database
	db1, err := sql.Open("pgx", "postgres://user1:secret@localhost:5432/user1?sslmode=disable")
	if err != nil {
		panic(err)
	}
	defer db1.Close()
	db2, err := sql.Open("pgx", "postgres://user2:secret@localhost:5433/user2?sslmode=disable")
	if err != nil {
		panic(err)
	}
	defer db2.Close()

	// Create some tables for testing
	// One table for users in db1
	_, err = db1.Exec("CREATE TABLE IF NOT EXISTS users (id uuid not null primary key, name text)")
	if err != nil {
		panic(err)
	}
	// One table for orders in db2
	_, err = db2.Exec(`CREATE TABLE IF NOT EXISTS orders(
        id uuid not null primary key, 
        user_id uuid not null, 
        amount int not null)`)
	if err != nil {
		panic(err)
	}

	userID := "47f89b20-cb3a-11ed-8475-aba23b81b15d"
	name := "John Doe"
	orderID := "a444eeaa-cb3b-11ed-a5c2-3b46183795fa"
	amount := 10

	// Create the participants for the 2 phase commit
	p1 := twophase.NewParticipant(db1, func(ctx context.Context, tx *sql.Tx) error {
		_, err := tx.ExecContext(ctx, "INSERT INTO users (id, name) VALUES ($1, $2)", userID, name)
		return err
	})

	p2 := twophase.NewParticipant(db2, func(ctx context.Context, tx *sql.Tx) error {
		_, err := tx.ExecContext(ctx, "INSERT INTO orders (id, user_id, amount) VALUES ($1, $2, $3)", orderID, userID, amount)
		return err
	})

	// setup the parameters for the transaction
	params := twophase.Params{
		Participants: []gosql2pc.Participant{p1, p2},
	}

	// run the transaction
	if err := twophase.Do(context.Background(), params); err != nil {
		panic(err)
	}
}

Examples

In the examples directory there is an executable with some examples.

cd examples
docker-compose up -d

then you can run the 3 examples. Please read the source code and it's comments.

go run main.go -cmd=basic
go run main.go -cmd=concurrency1
go run main.go -cmd=concurrency2

Caution

PostgreSQL has by default disabled the prepared_transactions. There is a good reason for that. You may even locked out of the database of permanently lock a table.

You need a mechanism that monitors that monitors any orphaned prepared transactions and takes action.

Please read the documentation and this blog post
and this blog post.

Don't be afraid but you should know with what you are dealing with.

In order to enable prepared transactions set in postgresql.conf max_prepared_transactions to something larger that zero. Better to set it to the number of max_connections

Alternatively, you can set it when you start the postgreSQL server by using the -c flag. (see the docker-compose.yaml in the examples folder).

The library gives you some level of consistency BUT when the process that coordinates the distributed transactions crashes you may leave orphan prepared transactions or having data inconsistency since only some of the participants may have finished the commits.

Additionally, if one participant manages to commit and the others don't (because of a disk failure for example) then again you may have data incosistency. I recommend to have some monitoring for these cases.

Consider if you actually need to phase commit or you can use maybe Sagas. Both patterns are useful, but I believe that Sagas are more generic since in order to use the 2 Phase Commit Protocol all the platforms need to implement the protocol. In any case distributed transactions are not trivial and you should be careful.

Contributing

Contributions to gosql2pc are always welcome. If you find a bug or want to suggest a new feature, please open an issue or submit a pull request.

LICENCE

gosql2pc is licensed under the MIT License. See the LICENSE file for more information.