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Reading large volumes of data in Go typically occurs on a replica configured as a read replica. This allows offloading the primary database (master) and increasing performance when executing heavy read queries.

For example, in architectures with PostgreSQL or MySQL databases, the main replica (master) handles write and read operations, while additional replicas are only for reading. In Go code, you can direct read queries specifically to the read replica to efficiently process large data volumes.

Example of using a read replica in Go with the database/sql library and custom query routing:

// dbMaster - connection to the master
// dbReplica - connection to the replica

func queryLargeData(readOnly bool) ([]Data, error) {
    var db *sql.DB
    if readOnly {
        db = dbReplica
    } else {
        db = dbMaster
    }
    rows, err := db.Query("SELECT * FROM large_table")
    if err != nil {
        return nil, err
    }
    defer rows.Close()

    var results []Data
    for rows.Next() {
        var d Data
        if err := rows.Scan(&d.Field1, &d.Field2); err != nil {
            return nil, err
        }
        results = append(results, d)
    }
    return results, nil
}

This way, large data volumes are read from the replica, reducing the load on the main database.