BlockRead, BlockWrite und die richtige Buffer-Größe

[Der schöne Günther]

Hier ein kleiner Test. Wenn ich hier auf ein Netzlaufwerk schreibe ist der TFileStream sogar schneller. Und mit einer anderen Blockgröße sogar noch schneller.

Zitat:

Time taken for block write: 2693 ms
Time taken for filestream, block size = 1: 8647 ms
Time taken for filestream, block size = 1024: 1341 ms
Time taken for filestream, block size = 50 * 4096: 1631 MS

Delphi-Quellcode:

program BlockWriteBenchmarkProject;

{$APPTYPE CONSOLE}
{$R *.res}

uses
  System.SysUtils,
  System.Diagnostics,
  System.IoUtils,
  System.Classes
;

const
   filePath      = 'T:\benchmark';
   bytesToWrite   = 100 * 1024 * 1024; // 100 MB
var
   fileStreamBlockSize: Integer;

procedure measureTime(const proc: TProcedure; const title: String);
var
   stopWatch: TStopwatch;
begin
   stopWatch := TStopwatch.StartNew();
   proc();
   stopWatch.Stop();
   WriteLn('Time taken for ', title, ': ', stopWatch.ElapsedMilliseconds, ' ms');
end;

procedure blockWriteThings();
const
   blockSize = 50 * 4096;
var
   legacyFile:      file;
   buffer:         TBytes;
   bytesWritten:   Int64;
begin
   SetLength(buffer, blockSize);
   bytesWritten := 0;

   AssignFile(legacyFile, filePath+'\blockwrite.abc');
   Rewrite(legacyFile, 1);
   try
      repeat
         BlockWrite(legacyFile, buffer[0], blockSize);
         Inc(bytesWritten, blockSize);
      until (bytesWritten = bytesToWrite);
   finally
      CloseFile(legacyFile)
   end;
end;

procedure fileStreamThings();
var
   fileStream:      TStream;
   bytesWritten:   Int64;
   buffer:         TBytes;
begin
   SetLength(buffer, fileStreamBlockSize);
   bytesWritten := 0;

   fileStream := TFile.Open(filePath + '\fileStream.abc', TFileMode.fmOpenOrCreate);
   try
      repeat
         fileStream.WriteData(buffer, fileStreamBlockSize);
         Inc(bytesWritten, fileStreamBlockSize)
      until (bytesWritten = bytesToWrite);
   finally
      fileStream.Destroy();
   end;
end;

begin
   measureTime(blockWriteThings, 'block write');

   fileStreamBlockSize := 1024;
   measureTime(fileStreamThings, 'filestream, block size = 1');

   fileStreamBlockSize := 1024 * 100;
   measureTime(fileStreamThings, 'filestream, block size = 1024');

   fileStreamBlockSize := 50 * 4096;
   measureTime(fileStreamThings, 'filestream, block size = 50 * 4096');


   readln;
end.

Jetzt bleibt nur noch die Frage, wie man die Blockgröße wählen sollte wenn man z.B. weiß dass man 100 MB schreiben möchte. Ich habe da nämlich auch keine Ahnung