问题
I need to open and read thousands of files as fast as possible.
I have ran a few tests on 13 592 files and found Method 1 to be slightly faster than Method 2. These files are usually between 800 bytes and 4kB. I would like to know if there is anything I can do to make this I/O-bound process faster?
Method 1:
Run 1: 3:05 (don't know what happened here)
Run 2: 1:55
Run 3: 2:06
Run 4: 2:02
Method 2:
Run 1: 2:04
Run 2: 2:08
Run 3: 2:04
Run 4: 2:12
Here's the code:
public class FileOpenerUtil
{
/// <summary>
///
/// </summary>
/// <param name="fullFilePath"></param>
/// <returns></returns>
public static string ReadFileToString(string fullFilePath)
{
while (true)
{
try
{
//Methode 1
using (StreamReader sr = File.OpenText(fullFilePath))
{
string fullMessage = "";
string s;
while ((s = sr.ReadLine()) != null)
{
fullMessage += s + "\n";
}
return RemoveCarriageReturn(fullMessage);
}
//Methode 2
/*using (File.Open(fullFilePath, FileMode.Open, FileAccess.Read, FileShare.Read))
{
Console.WriteLine("Output file {0} ready.", fullFilePath);
string[] lines = File.ReadAllLines(fullFilePath);
//Every new line under the previous line
string fullMessage = lines.Aggregate("", (current, s) => current + s + "\n");
return RemoveCarriageReturn(fullMessage);
//ninject kernel
}*/
//Methode 3
}
catch (FileNotFoundException ex)
{
Console.WriteLine("Output file {0} not yet ready ({1})", fullFilePath, ex.Message);
}
catch (IOException ex)
{
Console.WriteLine("Output file {0} not yet ready ({1})", fullFilePath, ex.Message);
}
catch (UnauthorizedAccessException ex)
{
Console.WriteLine("Output file {0} not yet ready ({1})", fullFilePath, ex.Message);
}
}
}
/// <summary>
/// Verwijdert '\r' in een string sequence
/// </summary>
/// <param name="message">The text that has to be changed</param>
/// <returns>The changed text</returns>
private static string RemoveCarriageReturn(string message)
{
return message.Replace("\r", "");
}
}
The files I'm reading are .HL7 files and look like this:
MSH|^~\&|OAZIS||||20150430235954||ADT^A03|23669166|P|2.3||||||ASCII EVN|A03|20150430235954||||201504302359 PID|1||6001144000||LastName^FirstName^^^Mevr.|LastName^FirstName|19600114|F|||GStreetName Number^^City^^PostalCode^B^H||09/3444556^^PH~0476519246echtg^^CP||NL|M||28783409^^^^VN|0000000000|60011402843||||||B||||N PD1||||003847^LastName^FirstName||||||||N|||0 PV1|1|O|FDAG^000^053^001^0^2|NULL||FDAG^000^053^001|003847^LastName^FirstName||006813^LastName^FirstName|1900|00||||||006813^LastName^FirstName|0|28783409^^^^VN|1^20150430|01|||||||||||||||1|1||D|||||201504301336|201504302359 OBX|1|CE|KIND_OF_DIS|RCM|1^1 Op medisch advies OBX|2|CE|DESTINATION_DIS|RCM|1^1 Terug naar huis
Once I opened the file, I parse the string with j4jayant's HL7 parser and close the file.
回答1:
I used 50,000 files of varying size (500 to 1024 bytes).
Test 1: Your method 1 StreamReader sr = File.OpenText(fullFilePath); sr.ReadLine();
Seconds: 3,4658937968113
Test 2: Your method 2 File.ReadAllLines(fullFilePath)
Seconds: 5,5008349279222
Test 3: File.ReadAllText(fullFilePath);
Seconds: 3,30782645637133
Test 4: BinaryReader b = new BinaryReader; b.ReadString();
Seconds: 5,85779941381009
Test 5: Windows FileReader (https://msdn.microsoft.com/en-us/library/2d9wy99d.aspx)
Seconds: 3,07036554759848
Test 6: StreamReader sr = File.OpenText(fullFilePath); sr.ReadToEnd();
Seconds: 3,31464109255517
Test 7: StreamReader sr = File.OpenText(fullFilePath); sr.ReadToEnd();
Seconds: 3,3364683664508
Test 8: StreamReader sr = File.OpenText(fullFilePath); sr.ReadLine();
Seconds: 3,40426888695317
Test 9: FileStream + BufferedStream + StreamReader
Seconds: 4,02871911079061
Test 10: Parallel.For using code File.ReadAllText(fullFilePath);
Seconds: 0,89543632235447
Best test results are Test 5 and Test 3 (single thread)
Test 3 is using: File.ReadAllText(fullFilePath);
Test 5 uses Windows FileReader (https://msdn.microsoft.com/en-us/library/2d9wy99d.aspx)
If you can use threads Test 10 is by far the quickest.
example:
int maxFiles = 50000;
int j = 0;
Parallel.For(0, maxFiles, x =>
{
Util.Method1("readtext_" + j + ".txt"); // your read method
j++;
});
When using RAMMap to empty the standby list:
Test 1: Your method 1 StreamReader sr = File.OpenText(fullFilePath);
sr.ReadLine();
Seconds: 15,1785750622961
Test 2: Your method 2 File.ReadAllLines(fullFilePath)
Seconds: 17,650864469466
Test 3: File.ReadAllText(fullFilePath);
Seconds: 14,8985912878328
Test 4: BinaryReader b = new BinaryReader; b.ReadString();
Seconds: 18,1603815767866
Test 5: Windows FileReader
Seconds: 14,5059765845334
Test 6: StreamReader sr = File.OpenText(fullFilePath); sr.ReadToEnd();
Seconds: 14,8649786336991
Test 7: StreamReader sr = File.OpenText(fullFilePath); sr.ReadToEnd();
Seconds: 14,830567197641
Test 8: StreamReader sr = File.OpenText(fullFilePath); sr.ReadLine();
Seconds: 14,9965866575751
Test 9: FileStream + BufferedStream + StreamReader
Seconds: 15,7336450516575
Test 10: Parallel.For() using code File.ReadAllText(fullFilePath);
Seconds: 4,11343060325439
回答2:
I have applied all code from the comments. Method 1 still seems to be the fastest.
public class FileOpenerUtil
{
/// <summary>
///
/// </summary>
/// <param name="fullFilePath"></param>
/// <returns></returns>
public static string ReadFileToString(string fullFilePath)
{
while (true)
{
try
{
//Method 1
using (StreamReader sr = File.OpenText(fullFilePath))
{
string s;
StringBuilder message = new StringBuilder();
while ((s = sr.ReadLine()) != null)
{
message.Append(s).Append("\n");
}
return RemoveCarriageReturn(message.ToString());
}
//Method 2
/*
string[] lines = File.ReadAllLines(fullFilePath);
string fullMessage = lines.Aggregate("", (current, s) => current + s + "\n");
return RemoveCarriageReturn(fullMessage);*/
}
//Method 3
/*
string s = File.ReadAllText(fullFilePath);
return RemoveCarriageReturn(s);*/
}
catch (FileNotFoundException ex)
{
Console.WriteLine("Output file {0} not yet ready ({1})", fullFilePath, ex.Message);
}
catch (IOException ex)
{
Console.WriteLine("Output file {0} not yet ready ({1})", fullFilePath, ex.Message);
}
catch (UnauthorizedAccessException ex)
{
Console.WriteLine("Output file {0} not yet ready ({1})", fullFilePath, ex.Message);
}
}
}
/// <summary>
/// Verwijdert '\r' in een string sequence
/// </summary>
/// <param name="message">The text that has to be changed</param>
/// <returns>The changed text</returns>
private static string RemoveCarriageReturn(string message)
{
return message.Replace("\r", "");
}
}
来源：https://stackoverflow.com/questions/36420013/open-and-read-thousands-of-files-as-fast-as-possible