How do you perform query replication and what experience can you share in this process?

Query replication in the context of Golang is usually associated with load balancing across multiple servers or databases to improve fault tolerance and performance. One common approach is to use a proxy server or load balancer that duplicates requests to several replicas.

In my experience, I implemented query replication at the application level, where read requests were directed to database replicas, and write requests to the primary server. For this, in Go, I used interfaces and the "repository" pattern to abstract data access logic and direct requests to the appropriate destination.

An example of a simplified implementation of selecting a replica for reading:

 type DB interface {
    Query(query string, args ...interface{}) (*sql.Rows, error)
    Exec(query string, args ...interface{}) (sql.Result, error)
}

// Primary server for writing
var masterDB DB
// Replicas for reading
var replicaDBs []DB

func QueryRead(query string, args ...interface{}) (*sql.Rows, error) {
    // Simple strategy: choose a random replica
    replica := replicaDBs[rand.Intn(len(replicaDBs))]
    return replica.Query(query, args...)
}

func ExecWrite(query string, args ...interface{}) (sql.Result, error) {
    return masterDB.Exec(query, args...)
}

It is also important to consider data consistency and replication lag to avoid reading stale data from replicas.