func (r *redirector) pgListener() {
var conn *pgx.Conn
listen := func() (err error) {
conn, err = r.DB.Acquire()
if err != nil {
return
}
if err = conn.Listen("refresh"); err != nil {
return
}
for {
_, err = conn.WaitForNotification(time.Second)
if err == pgx.ErrNotificationTimeout {
continue
}
if err != nil {
return
}
r.maybeLoad()
}
}
for {
err := listen()
log.Println("listen error:", err)
if conn != nil {
conn.Exec("UNLISTEN refresh")
r.DB.Release(conn)
conn = nil
}
time.Sleep(time.Second)
}
}
// afterConnect creates the prepared statements that this application uses
func afterConnect(conn *pgx.Conn) (err error) {
_, err = conn.Prepare("getUrl", `
select url from shortened_urls where id=$1
`)
if err != nil {
return
}
_, err = conn.Prepare("deleteUrl", `
delete from shortened_urls where id=$1
`)
if err != nil {
return
}
// There technically is a small race condition in doing an upsert with a CTE
// where one of two simultaneous requests to the shortened URL would fail
// with a unique index violation. As the point of this demo is pgx usage and
// not how to perfectly upsert in PostgreSQL it is deemed acceptable.
_, err = conn.Prepare("putUrl", `
with upsert as (
update shortened_urls
set url=$2
where id=$1
returning *
)
insert into shortened_urls(id, url)
select $1, $2 where not exists(select 1 from upsert)
`)
return
}
func TestPoolReleaseDiscardsDeadConnections(t *testing.T) {
t.Parallel()
maxConnections := 3
pool := createConnPool(t, maxConnections)
defer pool.Close()
var c1, c2 *pgx.Conn
var err error
var stat pgx.ConnPoolStat
if c1, err = pool.Acquire(); err != nil {
t.Fatalf("Unexpected error acquiring connection: %v", err)
}
defer func() {
if c1 != nil {
pool.Release(c1)
}
}()
if c2, err = pool.Acquire(); err != nil {
t.Fatalf("Unexpected error acquiring connection: %v", err)
}
defer func() {
if c2 != nil {
pool.Release(c2)
}
}()
if _, err = c2.Exec("select pg_terminate_backend($1)", c1.Pid); err != nil {
t.Fatalf("Unable to kill backend PostgreSQL process: %v", err)
}
// do something with the connection so it knows it's dead
rows, _ := c1.Query("select 1")
rows.Close()
if rows.Err() == nil {
t.Fatal("Expected error but none occurred")
}
if c1.IsAlive() {
t.Fatal("Expected connection to be dead but it wasn't")
}
stat = pool.Stat()
if stat.CurrentConnections != 2 {
t.Fatalf("Unexpected CurrentConnections: %v", stat.CurrentConnections)
}
if stat.AvailableConnections != 0 {
t.Fatalf("Unexpected AvailableConnections: %v", stat.CurrentConnections)
}
pool.Release(c1)
c1 = nil // so it doesn't get released again by the defer
stat = pool.Stat()
if stat.CurrentConnections != 1 {
t.Fatalf("Unexpected CurrentConnections: %v", stat.CurrentConnections)
}
if stat.AvailableConnections != 0 {
t.Fatalf("Unexpected AvailableConnections: %v", stat.CurrentConnections)
}
}