为什么 SQLite 数据库文件被锁定使用 WAL 模式并启用池化？

Question

我在我的 C# 程序中使用 SQLite 数据库。

程序每秒在数据库中保存值，并且每次都检查表是否已经存在：

class DataManager : IDataManager
{
    private bool machineTableIsCreated = false;
    private bool machineAlreadyInDb = false;
    private bool machineValueTableAlreadyExists = false;

    public DataManager()
    {
        machineTableIsCreated = CheckIfMachineTableExists();
    }

    //Writing the Values in a CSV-File
    public void WriteInCsv(dynamic value, string name)
    {
        string strFilePath = @"C:\SVN\" + name + ".csv";
        File.AppendAllText(strFilePath, Convert.ToString(value) + "\n");
    }

    //Writing the Values into the Database
    public void WriteInDb(string name, string netId, int port, List<BeckhoffVariable> variables)
    {
        BeckhoffMachineDto machine = new BeckhoffMachineDto
        {
            Name = name,
            NetId = netId,
            Port = port,
            Variables = variables
        };

        
        if (!machineTableIsCreated)
        {
            CreateMachineTable();
            machineTableIsCreated = true;
        }

        machineAlreadyInDb = CheckIfMachineIsAlreadyInDb(machine);
        if (!machineAlreadyInDb)
        {
            InsertMachineInDb(machine);
        }

        machineValueTableAlreadyExists = CheckIfMachineValueTableExists(machine.Name);
        if (!machineValueTableAlreadyExists)
        {
            //Creates Table for the Machine where its values are stored
            CreateTable(machine.Name);
        }

        //Inserts the Value read from the Machine into the DB
        InsertData(machine.Name, machine.Variables);
    }

    private bool CheckIfMachineValueTableExists(string name)
    {
        //Open connection to DB 
        using (var connection = new SQLiteConnection("Data Source=C:/SVN/trunk/database.db;PRAGMA journal_mode=WAL;Pooling=True;"))
        {
            connection.Open();

            //Creating Command to execute
            using (var command = connection.CreateCommand())
            {
                command.CommandText = $"SELECT * FROM SQLITE_MASTER WHERE type ='table' AND name ='{name}';";

                //read result of command
                using (var reader = command.ExecuteReader())
                {
                    //Check if result isnt null
                    if (reader.HasRows)
                    {
                        //connection.Close();
                        return true;
                    }
                    //connection.Close();
                    return false;
                }
            }
        }
    }

    private bool CheckIfMachineIsAlreadyInDb(BeckhoffMachineDto machine)
    {
        using (var connection = new SQLiteConnection("Data Source=C:/SVN/trunk/database.db;PRAGMA journal_mode=WAL;Pooling=True;"))
        {
            connection.Open();

            using (var command = connection.CreateCommand())
            {
                command.CommandText = $"SELECT * FROM machines WHERE Name = '{machine.Name}' AND NetId = '{machine.NetId.Replace('.', '-')}' AND Port = '{machine.Port}';";
                command.CommandTimeout = 1;

                using (var reader = command.ExecuteReader())
                {
                    if (reader.HasRows)
                    {
                        //connection.Close();
                        return true;
                    }
                    //connection.Close();
                    return false;
                }
            }
        }
    }

    private bool CheckIfMachineTableExists()
    {
        using (var connection = new SQLiteConnection("Data Source=C:/SVN/trunk/database.db;PRAGMA journal_mode=WAL;Pooling=True;"))
        {
            connection.Open();

            using (var command = connection.CreateCommand())
            {
                command.CommandText = "SELECT name FROM sqlite_master WHERE type='table' AND name='machines';";
                command.CommandTimeout = 1;

                using (var reader = command.ExecuteReader())
                {
                    if (reader.HasRows)
                    {
                        //connection.Close();
                        return true;
                    }
                    //connection.Close();
                    return false;
                }
            }
        }
    }

    private void InsertMachineInDb(BeckhoffMachineDto machine)
    {
        using (var connection = new SQLiteConnection("Data Source=C:/SVN/trunk/database.db;PRAGMA journal_mode=WAL;Pooling=True;"))
        {
            connection.Open();

            using (var command = connection.CreateCommand())
            {
                command.CommandText = "INSERT INTO machines (Name, NetId, Port, VariableCoolingFlow, VariableCoolingIn, VariableCoolingOut, " +
                "VariableTempAc, VariableTempDc, VariableTempAcBelow, VariableTempDcBelow) VALUES(@machineName, @machineNetId," +
                " @machinePort, @machineVar0, @machineVar1, @machineVar2, @machineVar3, @machineVar4, @machineVar5, @machineVar6); ";

                command.CommandType = CommandType.Text;
                command.Parameters.Add(new SQLiteParameter("@machineName", machine.Name));
                command.Parameters.Add(new SQLiteParameter("@machineNetId", machine.NetId.Replace('.', '-')));
                command.Parameters.Add(new SQLiteParameter("@machinePort", machine.Port));
                command.Parameters.Add(new SQLiteParameter("@machineVar0", machine.Variables[0].Name.Replace('.', '-')));
                command.Parameters.Add(new SQLiteParameter("@machineVar1", machine.Variables[1].Name.Replace('.', '-')));
                command.Parameters.Add(new SQLiteParameter("@machineVar2", machine.Variables[2].Name.Replace('.', '-')));
                command.Parameters.Add(new SQLiteParameter("@machineVar3", machine.Variables[3].Name.Replace('.', '-')));
                command.Parameters.Add(new SQLiteParameter("@machineVar4", machine.Variables[4].Name.Replace('.', '-')));
                command.Parameters.Add(new SQLiteParameter("@machineVar5", machine.Variables[5].Name.Replace('.', '-')));
                command.Parameters.Add(new SQLiteParameter("@machineVar6", machine.Variables[6].Name.Replace('.', '-')));

                command.ExecuteNonQuery();
            }
            //connection.Close();
        }
    }

    private static void CreateMachineTable()
    {
        using (var connection = new SQLiteConnection("Data Source=C:/SVN/trunk/database.db;PRAGMA journal_mode=WAL;Pooling=True;"))
        {
            connection.Open();

            using (var command = connection.CreateCommand())
            {
                command.CommandText = "CREATE TABLE machines (Name VARCHAR(40), NetId VARCHAR(30), Port VARCHAR(40), VariableCoolingFlow VARCHAR(45)," +
                " VariableCoolingIn VARCHAR(45), VariableCoolingOut VARCHAR(45), VariableTempAc VARCHAR(45), VariableTempDc VARCHAR(45)," +
                " VariableTempAcBelow VARCHAR(45), VariableTempDcBelow VARCHAR(45));";
                command.ExecuteNonQuery();
            }
            //connection.Close();
        }
    }

    //Creates The Tables for the Values a Machine has
    private static void CreateTable(string name)
    {
        using (var connection = new SQLiteConnection("Data Source=C:/SVN/trunk/database.db;PRAGMA journal_mode=WAL;Pooling=True;"))
        {
            connection.Open();

            using (var command = connection.CreateCommand())
            {
                command.CommandText = $"CREATE TABLE {name} (TemperatureCoolingFlow VARCHAR(20), TemperatureCoolingOut VARCHAR(20), TemperatureCoolingIn VARCHAR(20)," +
                " TemperatureDTSAc VARCHAR(20), TemperatureDTSDc VARCHAR(20), TemperatureDTSAcBelow VARCHAR(20), TemperatureDTSDcBelow VARCHAR(20))";

                command.ExecuteNonQuery();
            }
            //connection.Close();
        }
    }

    //Inserts the Machine Values in the Table of the Machine
    private static void InsertData(string name, List<BeckhoffVariable> variables)
    {
        using (var connection = new SQLiteConnection("Data Source=C:/SVN/trunk/database.db;PRAGMA journal_mode=WAL;Pooling=True;"))
        {
            connection.Open();

            using (var command = connection.CreateCommand())
            {
                command.CommandText = $"INSERT INTO {name} (TemperatureCoolingFlow, TemperatureCoolingOut, TemperatureCoolingIn, TemperatureDTSAc," +
                $" TemperatureDTSDc, TemperatureDTSAcBelow, TemperatureDTSDcBelow) VALUES(@machineVar0, @machineVar1, @machineVar2, " +
                $" @machineVar3, @machineVar4, @machineVar5, @machineVar6); ";

                command.CommandType = CommandType.Text;
                command.Parameters.Add(new SQLiteParameter("@machineVar0", Convert.ToString(variables[0].Value)));
                command.Parameters.Add(new SQLiteParameter("@machineVar1", Convert.ToString(variables[1].Value)));
                command.Parameters.Add(new SQLiteParameter("@machineVar2", Convert.ToString(variables[2].Value)));
                command.Parameters.Add(new SQLiteParameter("@machineVar3", Convert.ToString(variables[3].Value)));
                command.Parameters.Add(new SQLiteParameter("@machineVar4", Convert.ToString(variables[4].Value)));
                command.Parameters.Add(new SQLiteParameter("@machineVar5", Convert.ToString(variables[5].Value)));
                command.Parameters.Add(new SQLiteParameter("@machineVar6", Convert.ToString(variables[6].Value)));

                command.ExecuteNonQuery();
            }
            //connection.Close();
        }
    }

    //Returns a List of all Machines in the Database
    public List<BeckhoffMachineDto> getAllMachines()
    { 
        List<BeckhoffMachineDto> machines = new List<BeckhoffMachineDto>();

        using (var connection = new SQLiteConnection("Data Source=C:/SVN/trunk/database.db;PRAGMA journal_mode=WAL;Pooling=True;"))
        {
            connection.Open();

            machineTableIsCreated = CheckIfMachineTableExists();
            if (!machineTableIsCreated)
            {
                CreateMachineTable();
                machineTableIsCreated = true;
            }

            using (var command = connection.CreateCommand())
            {
                command.CommandText = "SELECT * FROM machines";

                using (var reader = command.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        BeckhoffMachineDto currMachine = new BeckhoffMachineDto();
                        currMachine.Name = (string)reader[0];
                        currMachine.NetId = reader[1].ToString().Replace('-', '.');
                        currMachine.Port = Convert.ToInt32(reader[2].ToString());
                        currMachine.Variables = new List<BeckhoffVariable>();

                        for (int i = 3; i <= 9; i++)
                        {
                            currMachine.Variables.Add(new BeckhoffVariable(reader[i].ToString().Replace('-', '.')));
                        }
                        machines.Add(currMachine);
                    }
                    //connection.Close();
                }
            }
        }
        return machines;
    }

    //Deletes the Machine from machines Table and deletes the whole Table from the given machine
    public void DeleteMachine(BeckhoffMachineDto selectedMachine)
    {
        using (var connection = new SQLiteConnection("Data Source=C:/SVN/trunk/database.db;PRAGMA journal_mode=WAL;Pooling=True;"))
        {
            connection.Open();

            using (var command = connection.CreateCommand())
            {
                command.CommandText = $"DROP TABLE {selectedMachine.Name}";
                command.ExecuteNonQuery();

                command.CommandText = $"DELETE FROM machines WHERE Name = '{selectedMachine.Name}' AND NetId = '{selectedMachine.NetId.Replace('.', '-')}' AND Port = '{selectedMachine.Port}'";
                command.ExecuteNonQuery();
            }
            //connection.Close();
        }
    }
}

问题是在运行程序中它被锁定了好几次。

我已经启用了 WAL 模式和 True 池。

我真的不明白它是如何被锁定的。

SQLite error (5): database is locked in "SELECT * FROM machines WHERE Name = 'Machine1' AND NetId = '10.10.10.1.1.1' AND Port = '111';"

SQLite error (5): database is locked in "SELECT * FROM machines WHERE Name = 'Machine1' AND NetId = '10.10.10.1.1.1' AND Port = '111';"

SQLite error (5): database is locked in "SELECT * FROM machines WHERE Name = 'Machine1' AND NetId = '10.10.10.1.1.1' AND Port = '111';"

SQLite error (5): database is locked in "SELECT * FROM machines WHERE Name = 'Machine1' AND NetId = '10.10.10.1.1.1' AND Port = '111';"

SQLite error (5): database is locked in "SELECT * FROM machines WHERE Name = 'Machine1' AND NetId = '10.10.10.1.1.1' AND Port = '111';"

问题是，当我将值写入数据库时，它会从数据库中选择一些内容并抛出数据库锁定错误，但 WAL 和池化应该会阻止这些。

有人知道我可以做些什么来解决我的问题吗？

Answer 1

看来，解决这个问题的方法是将sqlite数据库的同步pragma改为NORMAL！当使用 WAL 模式时，同步 pragma 的最佳设置是 NORMAL，但 db 的默认设置是 FULL。但是 FULL 不能很好地与 WAL 一起工作。当我更改它时，不再有数据库锁定错误。

为什么 SQLite 数据库文件被锁定使用 WAL 模式并启用池化？

Why the SQLite database file is locked using WAL Mode and Pooling enabled?

c#

sqlite

wal

database-concurrency

database-locking