Multinode database connector for GROM

Simple module to access multiple (Postgres or other) database nodes. Databases are divided into ONE write (or master) and MANY read (or slave) nodes. Replication is handled by the database and is not part of this module. You can choose for example bitnami/bitnami-docker-postgresql docker containers. They take care of replication.

A loss of a connection to any (including the master) of the nodes does not end up in a panic. Instead that node is marked as offline. If all read nodes are offline the the load will be redirected to the master. If the master is down no query can be processed but still if the nodes reconnect everything gets back to normal.

The distribution to read nodes is done randomly.

Under the hood this package uses GROM hooks. Similar to go-gorm/dbresolver.

Example

Lets start with one write and two read nodes.


import (
...
    "github.com/randree/multibase/v2"
...
)
func main() {
    logger := logger.New(
        log.New(os.Stdout, "\r\n", log.LstdFlags), // io writer
        logger.Config{
            SlowThreshold:             time.Second,   // Slow SQL threshold
            LogLevel:                  logger.Silent, // Log level
            IgnoreRecordNotFoundError: true,          // Ignore ErrRecordNotFound error for logger
            Colorful:                  false,         // Disable color
        },
    )
    // WRITE NODE
    nodeWrite := &multibase.NodeConf{
        Host:              "mycomputer",
        Port:              9000,
        User:              "database_user",
        Password:          "database_password",
        Sslmode:           "disable",
        TimeZone:           "Asia/Shanghai",
        Db:                "testdb",
        DbMaxOpenConns:    20,
        DbMaxIdleConns:    8,
        DbConnMaxLifetime: 1 * time.Hour,
        DbLogger:          logger,
    }
    // READ NODE 1
    nodeRead1 := &multibase.NodeConf{
        Host:              "mycomputer",
        Port:              9001,
        User:              "database_user", // User must be the master.
        Password:          "database_password",
        Sslmode:           "disable",
        TimeZone:           "Asia/Shanghai",
        Db:                "testdb",
        DbMaxOpenConns:    20,
        DbMaxIdleConns:    8,
        DbConnMaxLifetime: 1 * time.Hour,
        DbLogger:          logger,
    }
    // READ NODE 2
    nodeRead2 := &multibase.NodeConf{
        Host:              "mycomputer",
        Port:              9002,
        User:              "database_user",
        Password:          "database_password",
        Sslmode:           "disable",
        TimeZone:           "Asia/Shanghai",
        Db:                "testdb",
        DbMaxOpenConns:    20,
        DbMaxIdleConns:    8,
        DbConnMaxLifetime: 1 * time.Hour,
        DbLogger:          logger,
    }
    // OpenNode uses gorm.Open with DisableAutomaticPing: true
    // You can replace it by any other GORM opener
    // The result should be a *gorm.DB instance
    dbWrite, _ := multibase.OpenNode(nodeWrite) // Feel free to check err
    dbRead1, _ := multibase.OpenNode(nodeRead1)
    dbRead2, _ := multibase.OpenNode(nodeRead2)
    // Initiate multibase
    // At this stage NO actual connection is made
    mb := multibase.New(dbWrite, dbRead1, dbRead2)
    // The most important node is the write node.
    // We use the following lines of code to ping the write node and connect to it.
    // Even if no connection can be established, a panic does not occur.
    for {
        err := mb.ConnectWriteNode()
        if err != nil {
            fmt.Println(err)
        } else {
            break
        }
        time.Sleep(time.Millisecond * 1000) // You can choose the interval
    }
    // After the write node is set up, it is time to connect the read nodes
    err := mb.ConnectReadNodes()
    if err != nil {
        fmt.Println(err)
    }
    // After this is done, GetDatabaseReplicaSet binds all nodes to a GORM database
    // All read queries are forwarded to the read nodes.
    db := mb.GetDatabaseReplicaSet()
    // The StartReconnector is a go routine that checks the connection and 
    // reconnects to the nodes if necessary.
    mb.StartReconnector(time.Second * 1)
    // Now we can use db as usual
        type User struct {
        ID   int `gorm:"primarykey"`
        Name string
    }
    db.AutoMigrate(&User{})
    user := &User{}
    db.FirstOrInit(user, User{Name: "Jackx"})
    ...
    // To get some statistics use GetStatistics
    statistics := mb.GetStatistics()
    fmt.Println(statistics)
}

Statistics is a struct of following shape:

type Statistic struct {
    online               bool
    queryCount           int64
    errorCount           int64
    errorConnectionCount int64
}

The output is similar to

map[read0:{true 91214 3 0} read1:{true 98232 2 0} write:{true 234 0 0}]

Try it out

Use the docker-compose.yml to test the example.

Open two consoles.
In the first one spin up nodes with
```
$ docker-compose up -d
```

Write a main.go like one the above, add

 for {
     fmt.Print("\033[H\033[2J") // to clear the console after each cycle
     user := []User{}
     db.Find(&user)
     // Print out statistics
     fmt.Println(mb.GetStatistics())
     // map[read0:{true 1125 0 0} read1:{true 1087 0 0} write:{true 0 0 0}]
     time.Sleep(time.Millisecond * 100) // refresh each 100 ms
 }

In the second console run go

$ go run main.go

the result should be a similar to

map[read0:{true 91214 3 0} read1:{true 98232 2 0} write:{true 234 0 0}]

While the go program is running stop a read node with
```
$ docker stop read2
```
and see that all queries are forwarded to read0 (count starts at here at 0) and read1 (read2) is marked as offline.
Turn read2 on.
```
$ docker start read2
```
and the count is distributed between both read nodes.
Play around. Stop the write node. Stop all nodes. Then start all with docker start write read1 read2.

The program should never stop or panic.

Replication

Note that replication takes time in some cases. Try to avoid writing and reading the same data set in one routine.