From 7db509e682891f3bc501c7b23e32e02c64893557 Mon Sep 17 00:00:00 2001
From: Daniel Theophanes <kardianos@gmail.com>
Date: Sat, 29 Sep 2018 22:10:43 -0700
Subject: [PATCH] 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 #27792

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>
---
 src/database/sql/sql.go      | 10 ++++---
 src/database/sql/sql_test.go | 52 ++++++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+), 4 deletions(-)

diff --git a/src/database/sql/sql.go b/src/database/sql/sql.go
index 7537f87d47cf5..7c8d46b1008dc 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 f194744aefe72..e52091c3afd0c 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