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loadbalancer.go
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loadbalancer.go
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package dbresolver
import (
"context"
"math/rand"
"github.com/jmoiron/sqlx"
)
// LoadBalancer chooses a database from the given databases.
type LoadBalancer interface {
// Select returns the database to use for the given operation.
Select(ctx context.Context, dbs []*sqlx.DB) *sqlx.DB
}
// RandomLoadBalancer is a load balancer that chooses a database randomly.
type RandomLoadBalancer struct{}
var _ LoadBalancer = (*RandomLoadBalancer)(nil)
func NewRandomLoadBalancer() *RandomLoadBalancer {
return &RandomLoadBalancer{}
}
// Select returns the database to use for the given operation.
// If there are no databases, it returns nil. but it should not happen.
func (b *RandomLoadBalancer) Select(_ context.Context, dbs []*sqlx.DB) *sqlx.DB {
n := len(dbs)
if n == 0 {
return nil
}
if n == 1 {
return dbs[0]
}
return dbs[rand.Intn(n)]
}
// injectedLoadBalancer is a load balancer that always chooses the given database.
// It is used for testing.
type injectedLoadBalancer struct {
db *sqlx.DB
}
var _ LoadBalancer = (*injectedLoadBalancer)(nil)
func (b *injectedLoadBalancer) Select(_ context.Context, _ []*sqlx.DB) *sqlx.DB {
return b.db
}