为什么存储过程可以工作，但命令会引发超时？

问：

这是我的函数，应该插入一行（对不起我的英语不好）：addDocumentint,guid,string

internal static bool AddDocument(int userId, IFormFile document)
{
    using SqlCommand cmd = new() { CommandType = CommandType.StoredProcedure };
    cmd.BeginTransaction(IsolationLevel.ReadUncommitted);

    try
    {
        cmd.Parameters.Clear();
        cmd.CommandText = "UserDocument_Add";

        cmd.Parameters.Add("@UserId", SqlDbType.Int).Value = userId;
        cmd.Parameters.Add("@FileName", SqlDbType.NVarChar, 200).Value = document.FileName;

        var guid = Guid.NewGuid();
        cmd.Parameters.Add("@Guid", SqlDbType.UniqueIdentifier).Value = guid;

        // This line throws a timeout error
        var result = cmd.ExecuteReturnInt32(); 

        // <--more code-->

        return true;
    }
    catch
    {
        cmd.Rollback();
        return false;
    }
}

这是我在 SQL Server 中创建的存储过程：

CREATE PROCEDURE [dbo].[UserDocument_Add]
    @UserId int,
    @FileName nvarchar(200),
    @Guid uniqueidentifier
AS
BEGIN
    SET NOCOUNT ON;

    IF EXISTS (SELECT 1 FROM [User_Document] 
               WHERE (([UserId] = @UserId) AND (ExternalId = @Guid)))
    BEGIN
        RETURN -1;
    END

    INSERT INTO [User_Document] ([UserId], ExternalId, [FileName], CreatedBy)
    VALUES (@UserId, @Guid, @FileName, @UserId)

    RETURN 1
END