ConnPool.Begin retry logic checks connection IsAlive

ErrDeadConn is returned when calling an already dead connection. But the initial failure returns the real error. So we check for IsAlive instead of ErrDeadConn.

Added test for ConnPool.Begin retry logic.

conn_pool.go

@@ -228,13 +228,19 @@ func (p *ConnPool) BeginIso(iso string) (*Tx, error) {
 		}
 
 		tx, err := c.BeginIso(iso)
-		if err == ErrDeadConn {
-			p.Release(c)
-			continue
-		}
 		if err != nil {
+			alive := c.IsAlive()
 			p.Release(c)
-			return nil, err
+
+			// If connection is still alive then the error is not something trying
+			// again on a new connection would fix, so just return the error. But
+			// if the connection is dead try to acquire a new connection and try
+			// again.
+			if alive {
+				return nil, err
+			} else {
+				continue
+			}
 		}
 
 		tx.pool = p

conn_pool_test.go

@@ -363,41 +363,46 @@ func TestConnPoolTransactionIso(t *testing.T) {
 func TestConnPoolBeginRetry(t *testing.T) {
 	t.Parallel()
 
-	pool := createConnPool(t, 2)
-	defer pool.Close()
+	// Run timing sensitive test many times
+	for i := 0; i < 50; i++ {
+		func() {
+			pool := createConnPool(t, 2)
+			defer pool.Close()
 
-	killerConn, err := pool.Acquire()
-	if err != nil {
-		t.Fatal(err)
-	}
-	defer pool.Release(killerConn)
+			killerConn, err := pool.Acquire()
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer pool.Release(killerConn)
 
-	victimConn, err := pool.Acquire()
-	if err != nil {
-		t.Fatal(err)
-	}
-	pool.Release(victimConn)
+			victimConn, err := pool.Acquire()
+			if err != nil {
+				t.Fatal(err)
+			}
+			pool.Release(victimConn)
 
-	// Terminate connection that was released to pool
-	if _, err = killerConn.Exec("select pg_terminate_backend($1)", victimConn.Pid); err != nil {
-		t.Fatalf("Unable to kill backend PostgreSQL process: %v", err)
-	}
+			// Terminate connection that was released to pool
+			if _, err = killerConn.Exec("select pg_terminate_backend($1)", victimConn.Pid); err != nil {
+				t.Fatalf("Unable to kill backend PostgreSQL process: %v", err)
+			}
 
-	// Since victimConn is the only available connection in the pool, pool.Begin should
-	// try to use it, fail, and allocate another connection
-	tx, err := pool.Begin()
-	if err != nil {
-		t.Fatalf("pool.Begin failed: %v", err)
-	}
-	defer tx.Rollback()
+			// Since victimConn is the only available connection in the pool, pool.Begin should
+			// try to use it, fail, and allocate another connection
+			tx, err := pool.Begin()
+			if err != nil {
+				t.Fatalf("pool.Begin failed: %v", err)
+			}
+			defer tx.Rollback()
 
-	var txPid int32
-	err = tx.QueryRow("select pg_backend_pid()").Scan(&txPid)
-	if err != nil {
-		t.Fatalf("tx.QueryRow Scan failed: %v", err)
-	}
-	if txPid == victimConn.Pid {
-		t.Error("Expected txPid to defer from killed conn pid, but it didn't")
+			var txPid int32
+			err = tx.QueryRow("select pg_backend_pid()").Scan(&txPid)
+			if err != nil {
+				t.Fatalf("tx.QueryRow Scan failed: %v", err)
+			}
+			if txPid == victimConn.Pid {
+				t.Error("Expected txPid to defer from killed conn pid, but it didn't")
+			}
+		}()
 	}
 }