[release-branch.go1.11] database/sql: correctly report MaxIdleClosed stat

Previously the MaxIdleClosed counter was incremented when added
to the free connection list, rather then when it wasn't added
to the free connection list. Flip this logic to correct.

Fixes #28325

Change-Id: I405302c14fb985369dab48fbe845e5651afc4ccf
Reviewed-on: https://go-review.googlesource.com/c/138578
Run-TryBot: Daniel Theophanes <kardianos@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
(cherry picked from commit 7db509e682891f3bc501c7b23e32e02c64893557)
Reviewed-on: https://go-review.googlesource.com/c/146697
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Andrew Bonventre <andybons@golang.org>
Reviewed-by: Daniel Theophanes <kardianos@gmail.com>

2 files changed, 58 insertions, 4 deletions

diff --git a/src/database/sql/sql.go b/src/database/sql/sql.go
index 36179855db..44840b8798 100644
--- a/src/database/sql/sql.go
+++ b/src/database/sql/sql.go
@@ -1322,11 +1322,13 @@ func (db *DB) putConnDBLocked(dc *driverConn, err error) bool {
 			err:  err,
 		}
 		return true
-	} else if err == nil && !db.closed && db.maxIdleConnsLocked() > len(db.freeConn) {
-		db.freeConn = append(db.freeConn, dc)
+	} else if err == nil && !db.closed {
+		if db.maxIdleConnsLocked() > len(db.freeConn) {
+			db.freeConn = append(db.freeConn, dc)
+			db.startCleanerLocked()
+			return true
+		}
 		db.maxIdleClosed++
-		db.startCleanerLocked()
-		return true
 	}
 	return false
 }
diff --git a/src/database/sql/sql_test.go b/src/database/sql/sql_test.go
index f194744aef..e52091c3af 100644
--- a/src/database/sql/sql_test.go
+++ b/src/database/sql/sql_test.go
@@ -3415,6 +3415,58 @@ func TestConnectionLeak(t *testing.T) {
 	wg.Wait()
 }
 
+func TestStatsMaxIdleClosedZero(t *testing.T) {
+	db := newTestDB(t, "people")
+	defer closeDB(t, db)
+
+	db.SetMaxOpenConns(1)
+	db.SetMaxIdleConns(1)
+	db.SetConnMaxLifetime(0)
+
+	preMaxIdleClosed := db.Stats().MaxIdleClosed
+
+	for i := 0; i < 10; i++ {
+		rows, err := db.Query("SELECT|people|name|")
+		if err != nil {
+			t.Fatal(err)
+		}
+		rows.Close()
+	}
+
+	st := db.Stats()
+	maxIdleClosed := st.MaxIdleClosed - preMaxIdleClosed
+	t.Logf("MaxIdleClosed: %d", maxIdleClosed)
+	if maxIdleClosed != 0 {
+		t.Fatal("expected 0 max idle closed conns, got: ", maxIdleClosed)
+	}
+}
+
+func TestStatsMaxIdleClosedTen(t *testing.T) {
+	db := newTestDB(t, "people")
+	defer closeDB(t, db)
+
+	db.SetMaxOpenConns(1)
+	db.SetMaxIdleConns(0)
+	db.SetConnMaxLifetime(0)
+
+	preMaxIdleClosed := db.Stats().MaxIdleClosed
+
+	for i := 0; i < 10; i++ {
+		rows, err := db.Query("SELECT|people|name|")
+		if err != nil {
+			t.Fatal(err)
+		}
+		rows.Close()
+	}
+
+	st := db.Stats()
+	maxIdleClosed := st.MaxIdleClosed - preMaxIdleClosed
+	t.Logf("MaxIdleClosed: %d", maxIdleClosed)
+	if maxIdleClosed != 10 {
+		t.Fatal("expected 0 max idle closed conns, got: ", maxIdleClosed)
+	}
+}
+
 type nvcDriver struct {
 	fakeDriver
 	skipNamedValueCheck bool