Schnellster Weg, um große Daten in Textdatei Java zu schreiben
https://stackoverflow.com/questions/1062113
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Ich habe zu großen Daten in Text [csv] Datei zu schreiben. Ich benutzen BufferedWriter die Daten zu schreiben, und es dauerte etwa 40 Sekunden 174 MB Daten zu schreiben. Ist dies die schnellste Geschwindigkeit Java bieten?
bufferedWriter = new BufferedWriter ( new FileWriter ( "fileName.csv" ) );
Hinweis: Diese 40 Sekunden die Zeit von Iterieren umfassen und die Datensätze aus resultset auch holen. :). 174 mb ist für 400000 Zeilen des Suchresultates.
Lösung
Sie könnten versuchen, die BufferedWriter zu entfernen und nur das Filewriter direkt verwenden. Auf einem modernen System gibt es eine gute Chance, bist du einfach mal so in den Cache-Speicher des Laufwerks zu schreiben.
Es dauert im Bereich von 4-5 Sekunden 175MB (4.000.000 strings) zu schreiben - das ist auf einem Dual-Core 2,4 GHz Dell mit Windows XP mit einer 80GB, 7200 RPM Hitachi Festplatte
Können Sie isolieren, wie viel von der Zeit ist Abruf und wie viel ist das Schreiben von Dateien?
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;
import java.util.ArrayList;
import java.util.List;
public class FileWritingPerfTest {
private static final int ITERATIONS = 5;
private static final double MEG = (Math.pow(1024, 2));
private static final int RECORD_COUNT = 4000000;
private static final String RECORD = "Help I am trapped in a fortune cookie factory\n";
private static final int RECSIZE = RECORD.getBytes().length;
public static void main(String[] args) throws Exception {
List<String> records = new ArrayList<String>(RECORD_COUNT);
int size = 0;
for (int i = 0; i < RECORD_COUNT; i++) {
records.add(RECORD);
size += RECSIZE;
}
System.out.println(records.size() + " 'records'");
System.out.println(size / MEG + " MB");
for (int i = 0; i < ITERATIONS; i++) {
System.out.println("\nIteration " + i);
writeRaw(records);
writeBuffered(records, 8192);
writeBuffered(records, (int) MEG);
writeBuffered(records, 4 * (int) MEG);
}
}
private static void writeRaw(List<String> records) throws IOException {
File file = File.createTempFile("foo", ".txt");
try {
FileWriter writer = new FileWriter(file);
System.out.print("Writing raw... ");
write(records, writer);
} finally {
// comment this out if you want to inspect the files afterward
file.delete();
}
}
private static void writeBuffered(List<String> records, int bufSize) throws IOException {
File file = File.createTempFile("foo", ".txt");
try {
FileWriter writer = new FileWriter(file);
BufferedWriter bufferedWriter = new BufferedWriter(writer, bufSize);
System.out.print("Writing buffered (buffer size: " + bufSize + ")... ");
write(records, bufferedWriter);
} finally {
// comment this out if you want to inspect the files afterward
file.delete();
}
}
private static void write(List<String> records, Writer writer) throws IOException {
long start = System.currentTimeMillis();
for (String record: records) {
writer.write(record);
}
writer.flush();
writer.close();
long end = System.currentTimeMillis();
System.out.println((end - start) / 1000f + " seconds");
}
}
Andere Tipps
Memory-Mapped-Dateien versuchen (dauert 300 m / s 174MB in meinem m / c, Core 2 Duo, 2,5 GB RAM schreiben):
byte[] buffer = "Help I am trapped in a fortune cookie factory\n".getBytes();
int number_of_lines = 400000;
FileChannel rwChannel = new RandomAccessFile("textfile.txt", "rw").getChannel();
ByteBuffer wrBuf = rwChannel.map(FileChannel.MapMode.READ_WRITE, 0, buffer.length * number_of_lines);
for (int i = 0; i < number_of_lines; i++)
{
wrBuf.put(buffer);
}
rwChannel.close();
Nur aus Gründen der Statistik:
Die Maschine ist alt Dell mit neuen SSD
CPU: Intel Pentium D 2,8 Ghz
SSD: Patriot Inferno 120GB SSD
4000000 'records'
175.47607421875 MB
Iteration 0
Writing raw... 3.547 seconds
Writing buffered (buffer size: 8192)... 2.625 seconds
Writing buffered (buffer size: 1048576)... 2.203 seconds
Writing buffered (buffer size: 4194304)... 2.312 seconds
Iteration 1
Writing raw... 2.922 seconds
Writing buffered (buffer size: 8192)... 2.406 seconds
Writing buffered (buffer size: 1048576)... 2.015 seconds
Writing buffered (buffer size: 4194304)... 2.282 seconds
Iteration 2
Writing raw... 2.828 seconds
Writing buffered (buffer size: 8192)... 2.109 seconds
Writing buffered (buffer size: 1048576)... 2.078 seconds
Writing buffered (buffer size: 4194304)... 2.015 seconds
Iteration 3
Writing raw... 3.187 seconds
Writing buffered (buffer size: 8192)... 2.109 seconds
Writing buffered (buffer size: 1048576)... 2.094 seconds
Writing buffered (buffer size: 4194304)... 2.031 seconds
Iteration 4
Writing raw... 3.093 seconds
Writing buffered (buffer size: 8192)... 2.141 seconds
Writing buffered (buffer size: 1048576)... 2.063 seconds
Writing buffered (buffer size: 4194304)... 2.016 seconds
Wie wir die rohe Methode sehen langsamer die gepuffert ist.
Ihre Übertragungsgeschwindigkeit ist nicht wahrscheinlich durch Java beschränkt. Stattdessen würde ich (in keiner bestimmten Reihenfolge) vermuten
- die Geschwindigkeit der Übertragung aus der Datenbank
- die Geschwindigkeit der Übertragung auf die Festplatte
Wenn Sie den kompletten Datensatz lesen und es dann auf die Festplatte schreiben, dann länger das wird dauern, da die JVM Speicher zuweisen müssen, und der db rea / Plattenschreib sequentiell passieren. Stattdessen würde ich auf den gepufferte Schriftsteller schreibt für jeden gelesen, dass Sie aus der db zu machen, und so wird der Betrieb zu einem gleichzeitigen einem näher (ich weiß nicht, ob Sie das, oder nicht tun)
Für diese sperrigen von DB liest Sie Ihre Erklärung des abzustimmen möchten Größe holen . Es könnte eine Menge von Roundtrips zum DB speichern.
http : //download.oracle.com/javase/1.5.0/docs/api/java/sql/Statement.html#setFetchSize%28int%29
package all.is.well;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import junit.framework.TestCase;
/**
* @author Naresh Bhabat
*
Following implementation helps to deal with extra large files in java.
This program is tested for dealing with 2GB input file.
There are some points where extra logic can be added in future.
Pleasenote: if we want to deal with binary input file, then instead of reading line,we need to read bytes from read file object.
It uses random access file,which is almost like streaming API.
* ****************************************
Notes regarding executor framework and its readings.
Please note :ExecutorService executor = Executors.newFixedThreadPool(10);
* for 10 threads:Total time required for reading and writing the text in
* :seconds 349.317
*
* For 100:Total time required for reading the text and writing : seconds 464.042
*
* For 1000 : Total time required for reading and writing text :466.538
* For 10000 Total time required for reading and writing in seconds 479.701
*
*
*/
public class DealWithHugeRecordsinFile extends TestCase {
static final String FILEPATH = "C:\\springbatch\\bigfile1.txt.txt";
static final String FILEPATH_WRITE = "C:\\springbatch\\writinghere.txt";
static volatile RandomAccessFile fileToWrite;
static volatile RandomAccessFile file;
static volatile String fileContentsIter;
static volatile int position = 0;
public static void main(String[] args) throws IOException, InterruptedException {
long currentTimeMillis = System.currentTimeMillis();
try {
fileToWrite = new RandomAccessFile(FILEPATH_WRITE, "rw");//for random write,independent of thread obstacles
file = new RandomAccessFile(FILEPATH, "r");//for random read,independent of thread obstacles
seriouslyReadProcessAndWriteAsynch();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Thread currentThread = Thread.currentThread();
System.out.println(currentThread.getName());
long currentTimeMillis2 = System.currentTimeMillis();
double time_seconds = (currentTimeMillis2 - currentTimeMillis) / 1000.0;
System.out.println("Total time required for reading the text in seconds " + time_seconds);
}
/**
* @throws IOException
* Something asynchronously serious
*/
public static void seriouslyReadProcessAndWriteAsynch() throws IOException {
ExecutorService executor = Executors.newFixedThreadPool(10);//pls see for explanation in comments section of the class
while (true) {
String readLine = file.readLine();
if (readLine == null) {
break;
}
Runnable genuineWorker = new Runnable() {
@Override
public void run() {
// do hard processing here in this thread,i have consumed
// some time and eat some exception in write method.
writeToFile(FILEPATH_WRITE, readLine);
// System.out.println(" :" +
// Thread.currentThread().getName());
}
};
executor.execute(genuineWorker);
}
executor.shutdown();
while (!executor.isTerminated()) {
}
System.out.println("Finished all threads");
file.close();
fileToWrite.close();
}
/**
* @param filePath
* @param data
* @param position
*/
private static void writeToFile(String filePath, String data) {
try {
// fileToWrite.seek(position);
data = "\n" + data;
if (!data.contains("Randomization")) {
return;
}
System.out.println("Let us do something time consuming to make this thread busy"+(position++) + " :" + data);
System.out.println("Lets consume through this loop");
int i=1000;
while(i>0){
i--;
}
fileToWrite.write(data.getBytes());
throw new Exception();
} catch (Exception exception) {
System.out.println("exception was thrown but still we are able to proceeed further"
+ " \n This can be used for marking failure of the records");
//exception.printStackTrace();
}
}
}
