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 {
+		if err != nil {
+			alive := c.IsAlive()
 			p.Release(c)
+
+			// 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
 			}
-		if err != nil {
-			p.Release(c)
-			return nil, err
 		}
 
 		tx.pool = p

conn_pool_test.go

@@ -363,6 +363,9 @@ func TestConnPoolTransactionIso(t *testing.T) {
 func TestConnPoolBeginRetry(t *testing.T) {
 	t.Parallel()
 
+	// Run timing sensitive test many times
+	for i := 0; i < 50; i++ {
+		func() {
 			pool := createConnPool(t, 2)
 			defer pool.Close()
 
@@ -399,6 +402,8 @@ func TestConnPoolBeginRetry(t *testing.T) {
 			if txPid == victimConn.Pid {
 				t.Error("Expected txPid to defer from killed conn pid, but it didn't")
 			}
+		}()
+	}
 }
 
 func TestConnPoolQuery(t *testing.T) {