How to fast delete many files

Question

I have a folder in Windows Server with subfolders and ≈50000 files. When I click the right mouse button and choose delete (or shift+delete) – all files are deleted in 10-20 seco

Answer 1

Not quite sure why the method DirectoryInfo.Delete() takes too much time when deleting folders that have a lot of files and sub-folders. I suspect that the method may also do quite a few things that are unnecessary.

I write a small class to to use Win API without doing too many unnecessary things to test my idea. It takes about 40 seconds to delete a folder that have 50,000 files and sub-folders. So, hope it helps.

I use this PowerScript to generate the testing files.

$folder = "d:\test1";
For ($i=0; $i -lt 50000; $i++)
{
    New-Item -Path $folder -Name "test$i.txt" -ItemType "file" -Value $i.ToString();
}

The following is the code in C#.

using System;
using System.Collections.Generic;
//
using System.Runtime.InteropServices;
using System.IO;
//

namespace TestFileDelete
{
    class FileDelete
    {
        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
        struct WIN32_FIND_DATAW
        {
            public FileAttributes dwFileAttributes;
            public System.Runtime.InteropServices.ComTypes.FILETIME ftCreationTime;
            public System.Runtime.InteropServices.ComTypes.FILETIME ftLastAccessTime;
            public System.Runtime.InteropServices.ComTypes.FILETIME ftLastWriteTime;
            public UInt32 nFileSizeHigh;  //  DWORD
            public UInt32 nFileSizeLow;  //  DWORD
            public UInt32 dwReserved0;    //  DWORD
            public UInt32 dwReserved1;  //  DWORD
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]
            public String cFileName;
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 14)]
            public String cAlternateFileName;
        };


        static readonly IntPtr INVALID_HANDLE_VALUE = new IntPtr(-1);

        [DllImport("kernel32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
        private static extern IntPtr FindFirstFileW(String lpFileName, out WIN32_FIND_DATAW lpFindFileData);

        [DllImport("kernel32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
        private static extern Boolean FindNextFileW(IntPtr hFindFile, out WIN32_FIND_DATAW lpFindFileData);

        [DllImport("kernel32.dll")]
        private static extern Boolean FindClose(IntPtr handle);

        [DllImport("kernel32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
        public static extern Boolean DeleteFileW(String lpFileName);    //  Deletes an existing file

        [DllImport("kernel32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
        private static extern Boolean RemoveDirectoryW(String lpPathName);   //  Deletes an existing empty directory


        //  This method check to see if the given folder is empty or not.
        public static Boolean IsEmptyFolder(String folder)
        {
            Boolean res = true;

            if (folder == null && folder.Length == 0)
            {
                throw new Exception(folder + "is invalid");
            }

            WIN32_FIND_DATAW findFileData;
            String searchFiles = folder + @"\*.*";
            IntPtr searchHandle = FindFirstFileW(searchFiles, out findFileData);
            if (searchHandle == INVALID_HANDLE_VALUE)
            {
                throw new Exception("Cannot check folder " + folder);
            }

            do
            {
                if ((findFileData.dwFileAttributes & FileAttributes.Directory) == FileAttributes.Directory)
                {
                    //  found a sub folder
                    if (findFileData.cFileName != "." && findFileData.cFileName != "..")
                    {
                        res = false;
                        break;
                    }

                }   //  if ((findFileData.dwFileAttributes & FileAttributes.Directory) == FileAttributes.Directory)
                else
                {
                    //  found a file
                    res = false;
                    break;
                }
            } while (FindNextFileW(searchHandle, out findFileData));

            FindClose(searchHandle);
            return res;
        }   //  public static Boolean IsEmptyFolder(String folder)

        //  This method deletes the given folder
        public static Boolean DeleteFolder(String folder)
        {
            Boolean res = true;
            //  keep non-empty folders to delete later (after we delete everything inside)
            Stack<String> nonEmptyFolder = new Stack<String>();
            String currentFolder = folder;
            do
            {
                Boolean isEmpty = false;
                try
                {
                    isEmpty = IsEmptyFolder(currentFolder);
                }
                catch (Exception ex)
                {
                    //  Something wrong
                    res = false;
                    break;
                }

                if (!isEmpty)
                {
                    nonEmptyFolder.Push(currentFolder);
                    WIN32_FIND_DATAW findFileData;
                    IntPtr searchHandle = FindFirstFileW(currentFolder + @"\*.*", out findFileData);
                    if (searchHandle != INVALID_HANDLE_VALUE)
                    {
                        do
                        {   //  for each folder, find all of its sub folders and files
                            String foundPath = currentFolder + @"\" + findFileData.cFileName;
                            if ((findFileData.dwFileAttributes & FileAttributes.Directory) == FileAttributes.Directory)
                            {
                                //  found a sub folder
                                if (findFileData.cFileName != "." && findFileData.cFileName != "..")
                                {
                                    if (IsEmptyFolder(foundPath))
                                    {   //  found an empty folder, delete it
                                        if (!(res = RemoveDirectoryW(foundPath)))
                                        {
                                            Int32 error = Marshal.GetLastWin32Error();
                                            break;
                                        }
                                    }
                                    else
                                    {   //  found a non-empty folder
                                        nonEmptyFolder.Push(foundPath);
                                    }
                                }   //  if (findFileData.cFileName != "." && findFileData.cFileName != "..")

                            }   //  if ((findFileData.dwFileAttributes & FileAttributes.Directory) == FileAttributes.Directory)
                            else
                            {
                                //  found a file, delete it
                                if (!(res = DeleteFileW(foundPath)))
                                {
                                    Int32 error = Marshal.GetLastWin32Error();
                                    break;
                                }
                            }

                        } while (FindNextFileW(searchHandle, out findFileData));

                        FindClose(searchHandle);

                    }   //  if (searchHandle != INVALID_HANDLE_VALUE)

                }//  if (!IsEmptyFolder(folder))
                else
                {
                    if (!(res = RemoveDirectoryW(currentFolder)))
                    {
                        Int32 error = Marshal.GetLastWin32Error();
                        break;
                    }
                }

                if (nonEmptyFolder.Count > 0)
                {
                    currentFolder = nonEmptyFolder.Pop();
                }
                else
                {
                    currentFolder = null;
                }
            } while (currentFolder != null && res);

            return res;
        }   //  public static Boolean DeleteFolder(String folder)
    };

    class Program
    {
        static void Main(string[] args)
        {
            DateTime t1 = DateTime.Now;

            try
            {
                Boolean b = FileDelete.DeleteFolder(@"d:\test1");
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }

            DateTime t2 = DateTime.Now;
            TimeSpan ts = t2 - t1;
            Console.WriteLine(ts.Seconds);

        } 
    } 
}

Answer 2

A much faster way to delete files is to use the Windows functions instead of the .NET ones.

You will need to first import the function:

[DllImport("kernel32.dll", SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool DeleteFile(string lpFileName);

And then you can do this:

string[] files = Directory.EnumerateFiles(path, "*". SearchOption.AllDirectories);

foreach (string file in files)
{
    DeleteFile(file);
}

Once the files are deleted, which is the slowest part by using the managed APIs, you can call Directory.DeleteFolder(path, true) to delete the empty folders.

Answer 3

Since the question is actually about deleting network shared folders and it's stated that the explorer based delete is much faster than the C# internal delete mechanism, it might help to just invoke a windows shell based delete.

ProcessStartInfo Info = new ProcessStartInfo(); 
Info.Arguments = "/C rd /s /q \"<your-path>\""; 
Info.WindowStyle = ProcessWindowStyle.Hidden; 
Info.CreateNoWindow = true; 
Info.FileName = "cmd.exe"; 
Process.Start(Info);

Ofcourse, you have to replace <your-path>.

However, I don't have the infrastructure and files available to test the performance myself right now.