sqlstats: add Close method to Tracer

So users can count how often the conns close.

Updates tailscale/corp#33577

Signed-off-by: Brad Fitzpatrick <[email protected]>

Author: bradfitz

sqlite.go

@@ -119,6 +119,10 @@ func (drv) OpenConnector(name string) (driver.Connector, error) {
 	return &connector{name: name}, nil
 }
 
+// Connector returns a [driver.Connector] for the given connection
+// parameters.
+//
+// The tracer may be nil.
 func Connector(sqliteURI string, connInitFunc ConnInitFunc, tracer sqliteh.Tracer) driver.Connector {
 	return &connector{
 		name:         sqliteURI,
@@ -128,8 +132,10 @@ func Connector(sqliteURI string, connInitFunc ConnInitFunc, tracer sqliteh.Trace
 }
 
 // ConnectorWithLogger returns a [driver.Connector] for the given connection
-// parameters. makeLogger is used to create a [ConnLogger] when [Connect] is
+// parameters. makeLogger, if non-nil, is used to create a [ConnLogger] when [Connect] is
 // called.
+//
+// The tracer may also be nil.
 func ConnectorWithLogger(sqliteURI string, connInitFunc ConnInitFunc, tracer sqliteh.Tracer, makeLogger func() ConnLogger) driver.Connector {
 	return &connector{
 		name:         sqliteURI,
@@ -141,7 +147,7 @@ func ConnectorWithLogger(sqliteURI string, connInitFunc ConnInitFunc, tracer sql
 
 type connector struct {
 	name         string
-	tracer       sqliteh.Tracer
+	tracer       sqliteh.Tracer    // or nil
 	makeLogger   func() ConnLogger // or nil
 	connInitFunc ConnInitFunc
 }
@@ -193,7 +199,7 @@ const (
 type conn struct {
 	db       sqliteh.DB
 	id       sqliteh.TraceConnID
-	tracer   sqliteh.Tracer
+	tracer   sqliteh.Tracer // or nil if unused
 	logger   ConnLogger
 	stmts    map[string]*stmt // persisted statements
 	txState  txState
@@ -216,6 +222,9 @@ func (c *conn) Close() error {
 		delete(c.stmts, q)
 	}
 	err := reserr(c.db, "Conn.Close", "", c.db.Close())
+	if c.tracer != nil {
+		c.tracer.Close(c.id, err)
+	}
 	return err
 }
 

sqlite_test.go

@@ -634,6 +634,7 @@ func (t *queryTracer) Commit(_ sqliteh.TraceConnID, _ error) {
 }
 func (t *queryTracer) Rollback(_ sqliteh.TraceConnID, _ error) {
 }
+func (t *queryTracer) Close(_ sqliteh.TraceConnID, _ error) {}
 
 func TestTraceQuery(t *testing.T) {
 	tracer := &queryTracer{

sqliteh/sqliteh.go

@@ -909,4 +909,7 @@ type Tracer interface {
 
 	// Rollback is called by the driver to report the end of a Tx.
 	Rollback(id TraceConnID, err error)
+
+	// Close is called when the SQLite connection is closed.
+	Close(id TraceConnID, err error)
 }

sqlstats/sqlstats.go

@@ -28,6 +28,7 @@ type Tracer struct {
 	TxCommitError  *expvar.Map
 	TxRollback     *expvar.Map
 	TxTotalSeconds *expvar.Map
+	ConnCloses     *expvar.Int
 
 	curTxs sync.Map // TraceConnID -> *connStats
 
@@ -58,6 +59,9 @@ func (t *Tracer) Reset() {
 	if t.TxTotalSeconds != nil {
 		t.TxTotalSeconds.Init()
 	}
+	if t.ConnCloses != nil {
+		t.ConnCloses.Set(0)
+	}
 	t.curTxs.Range(func(key, value any) bool {
 		t.curTxs.Delete(key)
 		return true
@@ -376,3 +380,9 @@ func (t *Tracer) Handle(w http.ResponseWriter, r *http.Request) {
 	}
 	fmt.Fprintf(w, "</table></body></html>")
 }
+
+func (t *Tracer) Close(id sqliteh.TraceConnID, err error) {
+	if t.ConnCloses != nil {
+		t.ConnCloses.Add(1)
+	}
+}