Upgraded go & alpine, fix db checkpointing.

* Go version set to 1.19 in go.mod.
* Alpine upgraded to 3.16 in Dockerfile.
* DB restart checkpoint is forced manually after 15 mins of inactivity.
* DB truncate checkpoint is forced manually at exit.

server/server.go

@@ -26,12 +26,13 @@ import (
 var initDB string
 
 type Server struct {
-	config          ServerConfig
-	dbpool          *sqlitex.Pool
-	log             *logrus.Logger
-	ctx             context.Context
-	tileserverSvSet *mbsh.ServiceSet
-	mapPackSize     int64
+	config           ServerConfig
+	dbpool           *sqlitex.Pool
+	checkpointNotice chan struct{}
+	log              *logrus.Logger
+	ctx              context.Context
+	tileserverSvSet  *mbsh.ServiceSet
+	mapPackSize      int64
 }
 
 type ServerConfig struct {
@@ -75,15 +76,25 @@ func (s *Server) Run(ctx context.Context) {
 
 	<-s.ctx.Done()
 	s.log.Info("Shutting down server...")
+	defer s.log.Info("Server exitting.")
 
 	ctx, cancel := context.WithTimeout(context.Background(), time.Second*5)
 	defer cancel()
 	if err := server.Shutdown(ctx); err != nil {
 		s.log.WithError(err).Fatal("Server forced to shutdown.")
 	}
+	close(s.checkpointNotice)
+	s.log.Info("Closing db connection pool...")
 	s.dbpool.Close()
 
-	s.log.Info("Server exitting.")
+	// manually force truncate checkpoint
+	conn, err := sqlite.OpenConn(fmt.Sprintf("file:%s", s.config.DbPath), 0)
+	if err != nil {
+		s.log.WithError(err).Error("Failed to open connection for final checkpoint.")
+		return
+	}
+	s.checkpointDb(conn, true)
+	conn.Close()
 }
 
 func (s *Server) getDbConn() *sqlite.Conn {
@@ -95,12 +106,47 @@ func (s *Server) getDbConn() *sqlite.Conn {
 	return conn
 }
 
+func (s *Server) checkpointDb(conn *sqlite.Conn, truncate bool) {
+	var query string
+	if truncate {
+		query = "PRAGMA wal_checkpoint(TRUNCATE)"
+	} else {
+		query = "PRAGMA wal_checkpoint(RESTART)"
+	}
+	stmt, _, err := conn.PrepareTransient(query)
+	if err != nil {
+		s.log.WithError(err).Error("Failed to prepare checkpoint query.")
+		return
+	}
+	defer stmt.Finalize()
+
+	has, err := stmt.Step()
+	if err != nil {
+		s.log.WithError(err).Error("Failed to step through checkpoint query.")
+		return
+	}
+	if !has {
+		s.log.Error("Checkpoint query returned no rows.")
+		return
+	}
+
+	blocked := stmt.ColumnInt(0)
+	noWalPages := stmt.ColumnInt(1)
+	noReclaimedPages := stmt.ColumnInt(2)
+	if blocked == 1 {
+		s.log.Warn("Checkpoint query was blocked.")
+	}
+	s.log.Debugf("Checkpoint complete. %d pages written to WAL, %d pages written back to DB.", noWalPages, noReclaimedPages)
+}
+
 func (s *Server) setupDB() {
+	sqlitex.PoolCloseTimeout = time.Second * 10
 	dbpool, err := sqlitex.Open(fmt.Sprintf("file:%s", s.config.DbPath), 0, 10)
 	if err != nil {
 		s.log.WithError(err).Fatal("Failed to open/create DB.")
 	}
 	s.dbpool = dbpool
+	s.checkpointNotice = make(chan struct{})
 
 	if s.config.ReinitDB {
 		err = s.reinitDB()
@@ -108,6 +154,39 @@ func (s *Server) setupDB() {
 			s.log.WithError(err).Fatal("init DB transaction failed")
 		}
 	}
+
+	// aggressively checkpoint the database on idle times
+	go func() {
+		s.log.Debug("Starting manual restart checkpointing.")
+		defer s.log.Debug("Manual restart checkpointing stopped.")
+		delay := time.Minute * 15
+		var (
+			timer <-chan time.Time
+			ok    bool
+		)
+		for {
+			select {
+			case _, ok = <-s.checkpointNotice:
+				if !ok {
+					return
+				}
+				timer = time.After(delay)
+			case <-timer:
+				func() {
+					conn := s.dbpool.Get(s.ctx)
+					defer s.dbpool.Put(conn)
+					s.checkpointDb(conn, false)
+					timer = nil
+				}()
+			}
+		}
+	}()
+}
+
+func (s *Server) requestCheckpoint() {
+	go func() {
+		s.checkpointNotice <- struct{}{}
+	}()
 }
 
 func (s *Server) setupTiles() {
@@ -143,6 +222,7 @@ func (s *Server) reinitDB() error {
 	conn := s.getDbConn()
 	defer s.dbpool.Put(conn)
 
+	defer s.requestCheckpoint()
 	return sqlitex.ExecScript(conn, initDB)
 }
 
@@ -180,6 +260,7 @@ func (s *Server) handshake(hc models.HandshakeChallenge) (models.UserID, error)
 				return 0, err
 			}
 			id = ptrInt64(conn.LastInsertRowID())
+			s.requestCheckpoint()
 		}
 		return *id, nil
 	}()
@@ -395,6 +476,7 @@ func (s *Server) deleteExpiredFeatures(conn *sqlite.Conn) error {
 	if err != nil {
 		return fmt.Errorf("failed to delete expired features: %w", err)
 	}
+	s.requestCheckpoint()
 	return nil
 }
 
@@ -536,6 +618,7 @@ func (s *Server) addFeatures(conn *sqlite.Conn, features []models.Feature) (map[
 
 		localIDMapping[feature.ID] = models.FeatureID(conn.LastInsertRowID())
 	}
+	s.requestCheckpoint()
 	return localIDMapping, nil
 }
 
@@ -613,18 +696,26 @@ func (s *Server) addPhotos(conn *sqlite.Conn, createdFeatureMapping, addedFeatur
 		return nil
 	}
 
+	changed := false
+	defer func() {
+		if changed {
+			s.requestCheckpoint()
+		}
+	}()
 	for localFeatureID, photoNames := range createdFeatureMapping {
 		featureID, ok := createdIDMapping[localFeatureID]
 		if !ok {
 			return errs.NewErrFeatureForPhotoNotExists(int64(localFeatureID))
 		}
 		err = uploadPhotos(featureID, photoNames)
+		changed = true
 		if err != nil {
 			return fmt.Errorf("failed to upload photos for created features: %w", err)
 		}
 	}
 	for featureID, photoNames := range addedFeatureMapping {
 		err = uploadPhotos(featureID, photoNames)
+		changed = true
 		if err != nil {
 			return fmt.Errorf("failed to upload photos for existing features: %w", err)
 		}
@@ -682,6 +773,7 @@ func (s *Server) updateFeatures(conn *sqlite.Conn, features []models.Feature) er
 			return fmt.Errorf("failed to evaluate prepared statement: %w", err)
 		}
 	}
+	s.requestCheckpoint()
 	return nil
 }
 
@@ -709,6 +801,7 @@ func (s *Server) deleteFeatures(conn *sqlite.Conn, featureIDs []models.FeatureID
 			return fmt.Errorf("failed to evaluate prepared statement: %w", err)
 		}
 	}
+	s.requestCheckpoint()
 	return nil
 }
 
@@ -736,6 +829,7 @@ func (s *Server) deletePhotos(conn *sqlite.Conn, photoIDs []models.FeaturePhotoI
 			return fmt.Errorf("failed to evaluate prepared statement: %w", err)
 		}
 	}
+	s.requestCheckpoint()
 	return nil
 }