La forma más rápida de escribir datos enormes en archivos de texto Java

Tengo que escribir enormes datos en el archivo de texto [csv]. Usé BufferedWriter para escribir los datos y me tomó alrededor de 40 segundos escribir 174 mb de datos. ¿Es esta la velocidad más rápida que Java puede ofrecer?

bufferedWriter = new BufferedWriter ( new FileWriter ( "fileName.csv" ) ); 

Nota: Estos 40 segundos incluyen el tiempo de iterar y recuperar los registros del conjunto de resultados también. :). 174 mb es para 400000 filas en el conjunto de resultados.

Puede intentar eliminar el BufferedWriter y simplemente usar el FileWriter directamente. En un sistema moderno, hay muchas posibilidades de que simplemente esté escribiendo en la memoria caché de la unidad de todos modos.

Me lleva de 4 a 5 segundos escribir 175 MB (4 millones de cadenas), esto es en un Dell de doble núcleo a 2.4 GHz que ejecuta Windows XP con un disco Hitachi de 80 GB y 7200 RPM.

¿Puede aislar la cantidad de tiempo que es la recuperación de registros y cuánto se está escribiendo?

 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 records = new ArrayList(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 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 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 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"); } } 

intente con los archivos mapeados en memoria (toma 300 m / s para escribir 174MB en mi m / c, core 2 duo, 2.5GB RAM):

 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(); 

Solo por el bien de las estadísticas:

La máquina es vieja Dell con nueva 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 

Como podemos ver, el método crudo es más lento que el tamponado.

Su velocidad de transferencia probablemente no esté limitada por Java. En cambio, sospecho (sin ningún orden en particular)

  1. la velocidad de transferencia de la base de datos
  2. la velocidad de transferencia al disco

Si lee el conjunto de datos completo y luego lo escribe en el disco, eso llevará más tiempo, ya que la JVM tendrá que asignar memoria, y la escritura de db rea / disk ocurrirá secuencialmente. En su lugar, escribiría en el escritor en el búfer por cada lectura que realice desde la base de datos, por lo que la operación será más cercana a la simultánea (no sé si lo está haciendo o no)

Para estas voluminosas lecturas de DB es posible que desee ajustar el tamaño de búsqueda de su extracto . Puede ahorrar muchos viajes de ida y vuelta a DB.

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(); } } }