Make connection pool configurable

README.md

@@ -160,7 +160,7 @@ Steps:
     make static
     sudo ./bin/static/k8s-dqlite \
       --storage-dir /var/snap/microk8s/current/var/kubernetes/backend \
-      --listen unix:///var/snap/microk8s/current/var/kubernetes/backend/kine.sock
+      --listen unix:///var/snap/microk8s/current/var/kubernetes/backend/kine.sock:12379
     ```
 
 7. While developing and making changes to `k8s-dqlite`, just restart k8s-dqlite

cmd/root.go

@@ -9,6 +9,7 @@ import (
 	"os/signal"
 	"time"
 
+	"github.com/canonical/k8s-dqlite/pkg/kine/drivers/generic"
 	"github.com/canonical/k8s-dqlite/pkg/server"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"github.com/sirupsen/logrus"
@@ -32,6 +33,8 @@ var (
 		otel                   bool
 		otelAddress            string
 
+		connectionPoolConfig generic.ConnectionPoolConfig
+
 		watchAvailableStorageInterval time.Duration
 		watchAvailableStorageMinBytes uint64
 		lowAvailableStorageAction     string
@@ -108,6 +111,7 @@ var (
 				rootCmdOpts.admissionControlPolicy,
 				rootCmdOpts.acpLimitMaxConcurrentTxn,
 				rootCmdOpts.acpOnlyWriteQueries,
+				rootCmdOpts.connectionPoolConfig,
 				rootCmdOpts.watchQueryTimeout,
 			)
 			if err != nil {
@@ -176,6 +180,10 @@ func init() {
 	rootCmd.Flags().BoolVar(&rootCmdOpts.otel, "otel", false, "enable traces endpoint")
 	rootCmd.Flags().StringVar(&rootCmdOpts.otelAddress, "otel-listen", "127.0.0.1:4317", "listen address for OpenTelemetry endpoint")
 	rootCmd.Flags().StringVar(&rootCmdOpts.metricsAddress, "metrics-listen", "127.0.0.1:9042", "listen address for metrics endpoint")
+	rootCmd.Flags().IntVar(&rootCmdOpts.connectionPoolConfig.MaxIdle, "datastore-max-idle-connections", 5, "Maximum number of idle connections retained by datastore. If value = 0, the system default will be used. If value < 0, idle connections will not be reused.")
+	rootCmd.Flags().IntVar(&rootCmdOpts.connectionPoolConfig.MaxOpen, "datastore-max-open-connections", 5, "Maximum number of open connections used by datastore. If value <= 0, then there is no limit")
+	rootCmd.Flags().DurationVar(&rootCmdOpts.connectionPoolConfig.MaxLifetime, "datastore-connection-max-lifetime", 60*time.Second, "Maximum amount of time a connection may be reused. If value <= 0, then there is no limit.")
+	rootCmd.Flags().DurationVar(&rootCmdOpts.connectionPoolConfig.MaxIdleTime, "datastore-connection-max-idle-time", 0*time.Second, "Maximum amount of time a connection may be idle before being closed. If value <= 0, then there is no limit.")
 	rootCmd.Flags().DurationVar(&rootCmdOpts.watchAvailableStorageInterval, "watch-storage-available-size-interval", 5*time.Second, "Interval to check if the disk is running low on space. Set to 0 to disable the periodic disk size check")
 	rootCmd.Flags().Uint64Var(&rootCmdOpts.watchAvailableStorageMinBytes, "watch-storage-available-size-min-bytes", 10*1024*1024, "Minimum required available disk size (in bytes) to continue operation. If available disk space gets below this threshold, then the --low-available-storage-action is performed")
 	rootCmd.Flags().StringVar(&rootCmdOpts.lowAvailableStorageAction, "low-available-storage-action", "none", "Action to perform in case the available storage is low. One of (none|handover|terminate). none means no action is performed. handover means the dqlite node will handover its leadership role, if any. terminate means this dqlite node will shutdown")

pkg/kine/drivers/dqlite/dqlite.go

@@ -24,16 +24,16 @@ func init() {
 	}
 }
 
-func New(ctx context.Context, datasourceName string, tlsInfo tls.Config) (server.Backend, error) {
-	backend, _, err := NewVariant(ctx, datasourceName)
+func New(ctx context.Context, datasourceName string, tlsInfo tls.Config, connectionPoolConfig *generic.ConnectionPoolConfig) (server.Backend, error) {
+	backend, _, err := NewVariant(ctx, datasourceName, connectionPoolConfig)
 	return backend, err
 }
 
-func NewVariant(ctx context.Context, datasourceName string) (server.Backend, *generic.Generic, error) {
+func NewVariant(ctx context.Context, datasourceName string, connectionPoolConfig *generic.ConnectionPoolConfig) (server.Backend, *generic.Generic, error) {
 	logrus.Printf("New kine for dqlite")
 
 	// Driver name will be extracted from query parameters
-	backend, generic, err := sqlite.NewVariant(ctx, "", datasourceName)
+	backend, generic, err := sqlite.NewVariant(ctx, "", datasourceName, connectionPoolConfig)
 	if err != nil {
 		return nil, nil, errors.Wrap(err, "sqlite client")
 	}

pkg/kine/drivers/generic/generic.go

@@ -20,7 +20,10 @@ import (
 	"go.opentelemetry.io/otel/trace"
 )
 
-const otelName = "generic"
+const (
+	otelName            = "generic"
+	defaultMaxIdleConns = 2 // default from database/sql
+)
 
 var (
 	otelTracer       trace.Tracer
@@ -162,10 +165,32 @@ type Generic struct {
 	WatchQueryTimeout time.Duration
 }
 
-func configureConnectionPooling(db *sql.DB) {
-	db.SetMaxIdleConns(5)
-	db.SetMaxOpenConns(5)
-	db.SetConnMaxLifetime(60 * time.Second)
+type ConnectionPoolConfig struct {
+	MaxIdle     int
+	MaxOpen     int
+	MaxLifetime time.Duration
+	MaxIdleTime time.Duration
+}
+
+func configureConnectionPooling(connPoolConfig *ConnectionPoolConfig, db *sql.DB) {
+	// behavior of database/sql - zero means defaultMaxIdleConns; negative means 0
+	if connPoolConfig.MaxIdle < 0 {
+		connPoolConfig.MaxIdle = 0
+	} else if connPoolConfig.MaxIdle == 0 {
+		connPoolConfig.MaxIdle = defaultMaxIdleConns
+	}
+
+	logrus.Infof(
+		"Configuring database connection pooling: maxIdleConns=%d, maxOpenConns=%d, connMaxLifetime=%v, connMaxIdleTime=%v ",
+		connPoolConfig.MaxIdle,
+		connPoolConfig.MaxOpen,
+		connPoolConfig.MaxLifetime,
+		connPoolConfig.MaxIdleTime,
+	)
+	db.SetMaxIdleConns(connPoolConfig.MaxIdle)
+	db.SetMaxOpenConns(connPoolConfig.MaxOpen)
+	db.SetConnMaxLifetime(connPoolConfig.MaxLifetime)
+	db.SetConnMaxIdleTime(connPoolConfig.MaxIdleTime)
 }
 
 func q(sql, param string, numbered bool) string {
@@ -200,7 +225,7 @@ func openAndTest(driverName, dataSourceName string) (*sql.DB, error) {
 	return db, nil
 }
 
-func Open(ctx context.Context, driverName, dataSourceName string, paramCharacter string, numbered bool) (*Generic, error) {
+func Open(ctx context.Context, driverName, dataSourceName string, connPoolConfig *ConnectionPoolConfig, paramCharacter string, numbered bool) (*Generic, error) {
 	var (
 		db  *sql.DB
 		err error
@@ -219,7 +244,7 @@ func Open(ctx context.Context, driverName, dataSourceName string, paramCharacter
 		}
 	}
 
-	configureConnectionPooling(db)
+	configureConnectionPooling(connPoolConfig, db)
 
 	return &Generic{
 		DB: prepared.New(db),

pkg/kine/drivers/sqlite/sqlite.go

@@ -32,16 +32,16 @@ type opts struct {
 	admissionControlOnlyWriteQueries            bool
 }
 
-func New(ctx context.Context, dataSourceName string) (server.Backend, error) {
-	backend, _, err := NewVariant(ctx, "sqlite3", dataSourceName)
+func New(ctx context.Context, dataSourceName string, connectionPoolConfig *generic.ConnectionPoolConfig) (server.Backend, error) {
+	backend, _, err := NewVariant(ctx, "sqlite3", dataSourceName, connectionPoolConfig)
 	if err != nil {
 		return nil, err
 	}
 
 	return backend, err
 }
 
-func NewVariant(ctx context.Context, driverName, dataSourceName string) (server.Backend, *generic.Generic, error) {
+func NewVariant(ctx context.Context, driverName, dataSourceName string, connectionPoolConfig *generic.ConnectionPoolConfig) (server.Backend, *generic.Generic, error) {
 	const retryAttempts = 300
 
 	opts, err := parseOpts(dataSourceName)
@@ -65,7 +65,7 @@ func NewVariant(ctx context.Context, driverName, dataSourceName string) (server.
 		dataSourceName = "./db/state.db?_journal=WAL&cache=shared"
 	}
 
-	dialect, err := generic.Open(ctx, driverName, opts.dsn, "?", false)
+	dialect, err := generic.Open(ctx, driverName, opts.dsn, connectionPoolConfig, "?", false)
 	if err != nil {
 		return nil, nil, err
 	}

pkg/kine/drivers/sqlite/sqlite_test.go

@@ -5,7 +5,9 @@ import (
 	"database/sql"
 	"path"
 	"testing"
+	"time"
 
+	"github.com/canonical/k8s-dqlite/pkg/kine/drivers/generic"
 	"github.com/canonical/k8s-dqlite/pkg/kine/drivers/sqlite"
 	"github.com/sirupsen/logrus"
 )
@@ -51,7 +53,13 @@ func TestMigration(t *testing.T) {
 	}
 
 	ctx := context.Background()
-	if _, err := sqlite.New(ctx, dbPath); err != nil {
+	connPoolConfig := generic.ConnectionPoolConfig{
+		MaxIdle:     5,
+		MaxOpen:     5,
+		MaxLifetime: 60 * time.Second,
+		MaxIdleTime: 0 * time.Second,
+	}
+	if _, err := sqlite.New(ctx, dbPath, &connPoolConfig); err != nil {
 		t.Fatal(err)
 	}
 

pkg/kine/endpoint/endpoint.go

@@ -8,6 +8,7 @@ import (
 	"strings"
 
 	"github.com/canonical/k8s-dqlite/pkg/kine/drivers/dqlite"
+	"github.com/canonical/k8s-dqlite/pkg/kine/drivers/generic"
 	"github.com/canonical/k8s-dqlite/pkg/kine/drivers/sqlite"
 	"github.com/canonical/k8s-dqlite/pkg/kine/server"
 	"github.com/canonical/k8s-dqlite/pkg/kine/tls"
@@ -26,9 +27,10 @@ const (
 )
 
 type Config struct {
-	GRPCServer *grpc.Server
-	Listener   string
-	Endpoint   string
+	GRPCServer           *grpc.Server
+	Listener             string
+	Endpoint             string
+	ConnectionPoolConfig generic.ConnectionPoolConfig
 
 	tls.Config
 }
@@ -180,9 +182,9 @@ func getKineStorageBackend(ctx context.Context, driver, dsn string, cfg Config)
 	switch driver {
 	case SQLiteBackend:
 		leaderElect = false
-		backend, err = sqlite.New(ctx, dsn)
+		backend, err = sqlite.New(ctx, dsn, &cfg.ConnectionPoolConfig)
 	case DQLiteBackend:
-		backend, err = dqlite.New(ctx, dsn, cfg.Config)
+		backend, err = dqlite.New(ctx, dsn, cfg.Config, &cfg.ConnectionPoolConfig)
 	default:
 		return false, nil, fmt.Errorf("storage backend is not defined")
 	}

pkg/server/server.go

@@ -13,6 +13,7 @@ import (
 	"github.com/canonical/go-dqlite"
 	"github.com/canonical/go-dqlite/app"
 	"github.com/canonical/go-dqlite/client"
+	"github.com/canonical/k8s-dqlite/pkg/kine/drivers/generic"
 	"github.com/canonical/k8s-dqlite/pkg/kine/endpoint"
 	"github.com/canonical/k8s-dqlite/pkg/kine/server"
 	kine_tls "github.com/canonical/k8s-dqlite/pkg/kine/tls"
@@ -69,6 +70,7 @@ func New(
 	admissionControlPolicy string,
 	admissionControlPolicyLimitMaxConcurrentTxn int64,
 	admissionControlOnlyWriteQueries bool,
+	connectionPoolConfig generic.ConnectionPoolConfig,
 	watchQueryTimeout time.Duration,
 ) (*Server, error) {
 	var (
@@ -221,7 +223,8 @@ func New(
 		}
 		options = append(options, app.WithTLS(listen, dial))
 	}
-
+	// set datastore connection pool options
+	kineConfig.ConnectionPoolConfig = connectionPoolConfig
 	// handle tuning parameters
 	if exists, err := fileExists(dir, "tuning.yaml"); err != nil {
 		return nil, fmt.Errorf("failed to check for tuning.yaml: %w", err)