// OpenFromConnPool takes the existing *pgx.ConnPool pool and returns a *sql.DB
// with pool as the backend. This enables full control over the connection
// process and configuration while maintaining compatibility with the
// database/sql interface. In addition, by calling Driver() on the returned
// *sql.DB and typecasting to *stdlib.Driver a reference to the pgx.ConnPool can
// be reaquired later. This allows fast paths targeting pgx to be used while
// still maintaining compatibility with other databases and drivers.
//
// pool connection size must be at least 2.
func OpenFromConnPool(pool *pgx.ConnPool) (*sql.DB, error) {
d := &Driver{Pool: pool}
name := fmt.Sprintf("pgx-%d", openFromConnPoolCount)
openFromConnPoolCount++
sql.Register(name, d)
db, err := sql.Open(name, "")
if err != nil {
return nil, err
}
// Presumably OpenFromConnPool is being used because the user wants to use
// database/sql most of the time, but fast path with pgx some of the time.
// Allow database/sql to use all the connections, but release 2 idle ones.
// Don't have database/sql immediately release all idle connections because
// that would mean that prepared statements would be lost (which kills
// performance if the prepared statements constantly have to be reprepared)
stat := pool.Stat()
if stat.MaxConnections <= 2 {
return nil, errors.New("pool connection size must be at least 2")
}
db.SetMaxIdleConns(stat.MaxConnections - 2)
db.SetMaxOpenConns(stat.MaxConnections)
return db, nil
}
