ObjectOutputStream送出的物件指向舊的物件?

假設我在Server端有以下的Code

HashMap<String,String> map=new HashMap<String,String> ();
ObjectOutputStream oos=new ObjectOutputStream(clientsocket.getOutputStream);
while(true){
       map.put(Long.toString(System.currentTimeMillis()),Long.toString(System.currentTimeMillis()));
       oos.writeObject(map);
}

另外一端收到的會發現後面收到的物件都跟第一次收到的物件一樣，Why?因為在送出的時候都是指向同一個位址，因此必須要加上oos.reset();結果才會正確。

File Transfer via Network using C vs. JAVA

這次的測試分別比較了使用gcc /gcc -O2 編譯而成的與javac 1.6.0_23 的版本編譯而成的執行檔來做比較，測試的兩台機器是在Lan環境下。測試的設備與程式碼如下:

CPU	Intel(R) Core(TM) i7 CPU         950  @ 3.07GHz
MEMERY	6G
NETWORK	1G
TEST FILE	466819755 byte (tar.bz2 file)

測試程式如下:
C (copy from http://content.edu.tw/primary/info_edu/cy_sa/report/more/8611a8.htm)
server.c

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#define TRUE 1
main()
{
int sock, msgsock, length;
struct sockaddr_in name;
FILE *fp;
int rval,wrval;
char buf[1024],filename[1024];

sock = socket(AF_INET, SOCK_STREAM, 0);
if (sock < 0) {
perror("opening stream socket");
exit(1);
}
/*-------------------------------------------------------*/
/* Create the acceptable connection host with Wildcard */
/*-------------------------------------------------------*/
name.sin_family = AF_INET;
name.sin_addr.s_addr = INADDR_ANY;
name.sin_port = 5000;
if (bind(sock, (struct sockaddr *)&name, sizeof name) < 0) {
perror ("binding stream socket");
exit(1);
}
listen(sock,5);
do{
msgsock = accept(sock,(struct sockaddr *)0, (int *)0);
if (msgsock == -1)
perror("accept error !\\n ");
else do {
bzero(buf, sizeof(buf) );
/*--------------------------------------------------*/
/* Read filename from msgsock (sent from client) */
/*--------------------------------------------------*/
if ((rval = read(msgsock, buf,1024)) < 0)
perror("reading stream message");
if (rval == 0)
printf("Ending connection\\n");
else {
if ((fp=fopen(buf,"r")) == NULL) {
printf("file not found : %s !\\n ",buf);
break;
}
printf("opening [%s] !!\\n ",buf);
bzero(filename,sizeof(filename));
strcpy(filename, buf);
/*--------------------------------------------------*/
/* Read file content & sent to msgsock ...> client */
/*--------------------------------------------------*/
while (fgets(buf,sizeof(buf),fp) != (char*)NULL) {
if ((wrval=write(msgsock,buf,sizeof(buf))) <0)
break;
//printf(".");
}
fclose(fp);
printf("\\n\\n closing [%s] ! \\n",filename);
rval=0;
}
}while (rval != 0);
close(msgsock);
printf(" [%s]finish* !! \\n ",filename);
}while (TRUE);
close(sock);
exit(0);
}

client.c

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#define DATA "The sea is clam ...."
main(int argc, char *argv[] )
{
int sock, rval, wrval;
char buf[1024];
struct sockaddr_in server;
struct hostent *hp, *gethostbyname();
FILE *fp;

sock = socket(AF_INET,SOCK_STREAM,0);
if (sock < 0) {
perror("opening stream socket");
exit(1);
}
server.sin_family=AF_INET;
hp=gethostbyname(argv[1]);
if (hp == 0 ) {
printf( "%s : unknown host\\n", argv[1]);
exit(2);
}
bcopy((char*)hp->h_addr, (char *)&server.sin_addr, hp->h_length);
server.sin_port = 5000;
if (connect(sock, (struct sockaddr *)&server, sizeof server) < 0)
{
perror ("connecting stream socket");
exit(1);
}

if (write(sock, argv[3],strlen(argv[3])) < 0)
perror ("writing stream socket");
sleep(1);
printf("requiring [%s], ...\\n",argv[3]);
fp=fopen(argv[4],"w+");
/*---------------------------------------------------------*/
/* Read file content from sock (sent from ftp_serv ) */
/* and Write to local file */
/*---------------------------------------------------------*/
while ( (rval=read(sock,buf,sizeof(buf) )) >1) {
//printf(".");
fputs(buf,fp);
}
fclose(fp);
close(sock);
printf("finish !! \\n");
printf("closing connection !! \\n");
exit(0);
}

JAVA
server.java

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;

public class server {
  public static void main(String[] args) throws IOException {
    ServerSocket servsock = new ServerSocket(5000);
    File myFile = new File("hadoop.tar.bz2");
    while (true) {
      Socket sock = servsock.accept();
      byte[] mybytearray = new byte[(int) myFile.length()];
      BufferedInputStream bis = new BufferedInputStream(new FileInputStream(myFile));
      bis.read(mybytearray, 0, mybytearray.length);
      OutputStream os = sock.getOutputStream();
      os.write(mybytearray, 0, mybytearray.length);
      os.flush();
      sock.close();
    }
  }
}

client.java

import java.io.BufferedOutputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.Socket;

public class client {
  public static void main(String[] argv) throws Exception {
    Socket sock = new Socket("192.168.254.1", 5000);
    byte[] mybytearray = new byte[1024];
    InputStream is = sock.getInputStream();
    FileOutputStream fos = new FileOutputStream("hadoop.tar.bz2");
    BufferedOutputStream bos = new BufferedOutputStream(fos);
    int bytesRead ;
   while((bytesRead= is.read(mybytearray, 0, mybytearray.length))!=-1){
    bos.write(mybytearray, 0, bytesRead);
    }
    bos.close();
    sock.close();
  }
}

測試結果如下:

Test Case	Time(s)
C with -O2	20.539(s)
C without -O2	20.286(s)
JAVA	4.923(s)

很詭異的結果，再研究看看。

Java的List, Set, Map比較

首先我主要比較了
List: ArrayList, LinkedList
Set: HashSet, TreeSet
Map: HashMap, TreeMap
並且針對了這幾個新增刪除以及取得(Get)來做比較，測試方式是先新增10000個字串物件，然後刪除字串為"5000”的物件，再來則是利用while loop及foreach來展開全部的物件。
實驗環境為

CPU	Intel core i7 860 @2.80GHz
OS	WIndows 7 X86_64
MEM	6G
JDK	Java SE 6 Update 23

以下為數據結果:

	add(push)	delete(remove)	Get(foreach)	Get (while)
ArrayList	10	1	2	4
LinkedList	4	1	1	4
HashSet	13	0	2	5
TreeSet	38	0	4	6
HashMap	3	0	N/A	4
TreeMap	7	0	N/A	4

程式碼如下

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.TreeMap;
import java.util.TreeSet;


public class PerformanceTest {
 
 private static void ArrayListTest(int size){
  System.out.println("\nArrayListTest, Total size: "+size);
  ArrayList<String> list=new ArrayList<String>();
  long start=System.currentTimeMillis();
  for(int i=0;i<size;i++){
   list.add(Integer.toString(i));
  }
  System.out.println("1.Add time: "+(System.currentTimeMillis()-start)+" (ms)");
  
  start=System.currentTimeMillis();
  
   list.remove(Integer.toString(size/2));
  
  System.out.println("2.Delete time(delete the object "+size/2+") :"+(System.currentTimeMillis()-start)+" (ms)");
  
  start=System.currentTimeMillis();
  Iterator iterator = list.iterator();
  String s;
        while(iterator.hasNext()) {
         s=(String) iterator.next();
        }
  System.out.println("3.Get time(use iterator): "+(System.currentTimeMillis()-start)+" (ms)");
  
  start=System.currentTimeMillis();
  for(String i : list) {
   s=i;
        }
  System.out.println("4.Get time(use enhanced for loop): "+(System.currentTimeMillis()-start)+" (ms)");
 }
 
 private static void LinkedListTest(int size){
  System.out.println("\nLinkedListTest, Total size: "+size);
  LinkedList<String> list=new LinkedList<String>();
  long start=System.currentTimeMillis();
  for(int i=0;i<size;i++){
   list.add(Integer.toString(i));
  }
  System.out.println("1.Add time: "+(System.currentTimeMillis()-start)+" (ms)");
  
  start=System.currentTimeMillis();
  
   list.remove(Integer.toString(size/2));
  
  System.out.println("2.Delete time(delete the object "+size/2+") :"+(System.currentTimeMillis()-start)+" (ms)");
  
  start=System.currentTimeMillis();
  Iterator iterator = list.iterator();
  String s;
        while(iterator.hasNext()) {
         s=(String) iterator.next();
        }
  System.out.println("3.Get time(use iterator): "+(System.currentTimeMillis()-start)+" (ms)");
  
  start=System.currentTimeMillis();
  for(String i : list) {
   s=i;
        }
  System.out.println("4.Get time(use enhanced for loop): "+(System.currentTimeMillis()-start)+" (ms)");
 }
 
 private static void HashSetTest(int size){
  System.out.println("\nHashSetTest, Total size: "+size);
  HashSet<String> list=new HashSet<String>();
  long start=System.currentTimeMillis();
  for(int i=0;i<size;i++){
   list.add(Integer.toString(i));
  }
  System.out.println("1.Add time: "+(System.currentTimeMillis()-start)+" (ms)");
  
  start=System.currentTimeMillis();
  
   list.remove(Integer.toString(size/2));
  
   System.out.println("2.Delete time(delete the object "+size/2+") :"+(System.currentTimeMillis()-start)+" (ms)");
  
  start=System.currentTimeMillis();
  Iterator iterator = list.iterator();
  String s;
        while(iterator.hasNext()) {
         s=(String) iterator.next();
        }
  System.out.println("3.Get time(use iterator): "+(System.currentTimeMillis()-start)+" (ms)");
  
  start=System.currentTimeMillis();
  for(String i : list) {
   s=i;
        }
  System.out.println("4.Get time(use enhanced for loop): "+(System.currentTimeMillis()-start)+" (ms)");
 }
 
 private static void TreeSetTest(int size){
  System.out.println("\nTreeSetTest, Total size: "+size);
  TreeSet<String> list=new TreeSet<String>();
  long start=System.currentTimeMillis();
  for(int i=0;i<size;i++){
   list.add(Integer.toString(i));
  }
  System.out.println("1.Add time: "+(System.currentTimeMillis()-start)+" (ms)");
  
  start=System.currentTimeMillis();
  
   list.remove(Integer.toString(size/2));
  
   System.out.println("2.Delete time(delete the object "+size/2+") :"+(System.currentTimeMillis()-start)+" (ms)");
  
  start=System.currentTimeMillis();
  Iterator iterator = list.iterator();
  String s;
        while(iterator.hasNext()) {
         s=(String) iterator.next();
        }
  System.out.println("3.Get time(use iterator): "+(System.currentTimeMillis()-start)+" (ms)");
  
  start=System.currentTimeMillis();
  for(String i : list) {
   s=i;
        }
  System.out.println("4.Get time(use enhanced for loop): "+(System.currentTimeMillis()-start)+" (ms)");
 }
 
 private static void HashMapTest(int size){
  System.out.println("\nHashMapTest, Total size: "+size);
  HashMap<String,String> list=new HashMap<String,String>();
  long start=System.currentTimeMillis();
  for(int i=0;i<size;i++){
   list.put(Integer.toString(i),Integer.toString(i));
  }
  System.out.println("1.Add time: "+(System.currentTimeMillis()-start)+" (ms)");
  
  start=System.currentTimeMillis();
  
   list.remove(Integer.toString(size/2));
  
   System.out.println("2.Delete time(delete the object "+size/2+") :"+(System.currentTimeMillis()-start)+" (ms)");
  
  start=System.currentTimeMillis();
  Collection collection = list.values();
        Iterator iterator = collection.iterator();
        String s;
        while(iterator.hasNext()) {
            s=(String) iterator.next();
        }
  System.out.println("3.Get time(use iterator): "+(System.currentTimeMillis()-start)+" (ms)");
  
  
 }
 
 private static void TreeMapTest(int size){
  System.out.println("\nTreeMapTest, Total size: "+size);
  TreeMap<String,String> list=new TreeMap<String,String>();
  long start=System.currentTimeMillis();
  for(int i=0;i<size;i++){
   list.put(Integer.toString(i),Integer.toString(i));
  }
  System.out.println("1.Add time: "+(System.currentTimeMillis()-start)+" (ms)");
  
  start=System.currentTimeMillis();
  
   list.remove(Integer.toString(size/2));
  
   System.out.println("2.Delete time(delete the object "+size/2+") :"+(System.currentTimeMillis()-start)+" (ms)");
  
  start=System.currentTimeMillis();
  Collection collection = list.values();
        Iterator iterator = collection.iterator();
        String s;
        while(iterator.hasNext()) {
            s=(String) iterator.next();
        }
  System.out.println("3.Get time(use iterator): "+(System.currentTimeMillis()-start)+" (ms)");
  
  
 }
 public static void main(String[] args) {
  ArrayListTest(10000);
  LinkedListTest(10000);
  HashSetTest(10000);
  TreeSetTest(10000);
  HashMapTest(10000);
  TreeMapTest(10000);
 }
}

HDFS Performance Test

很久很久以前就想測測看了！測試的項目主要有:
1.使用fuse掛載HDFS然後測試使用cp上傳下載以及使用dd產生檔案的速度
2.使用command (hadoop dfs –get/-put )取得效能
過幾天再補一個使用HDFS API來寫檔的速度好了。
以下是測試結果:

我的結論是:1.在小檔案方面基本上可以以忽略的，誤差很大(因為檔案太小)
                    2.下載比上傳快(差異蠻大的)
                    3.使用fuse掛載會慢一點點
                    4..另外參考一個數值:兩台電腦使用scp傳輸1GB時間是23秒(43.5MB/s)

Ubuntu Software RAID 5

之前拿四顆硬碟分別是 Seagate的2T*1  1.5T*3，簡單測一下效能:
A.對照組:在其中一個1.5T的硬碟切一個266G的磁區格式化為EXT4
B.實驗組:把剩下的空間作成RAID5 所以有5.7T也是格式化為EXT4
實驗方式是以dd的指令來產生檔案，bs為512K，連續跑四次扣除最快和最慢的取平均。
         1K B          512KB              1MB            10MB             100MB            1GB              10GB
A   48.9MB/s    700.5MB/s      822.5/MB/s    1091MB/s      1700MB/s       45MB/s          46MB/s
B  22.2 MB/s     553 MB/s        787MB/s       1331MB/s      1700MB/s      363MB/s        120MB/s

簡單的結論: Softraid 5 在檔案超過10MB後寫入效能會比單顆硬碟好。

在Ubuntu解決使用lftp亂碼問題

lftp是一個很好用的工具，特別是對於我這個重度ftp的人！然而，有些人就是很喜歡使用Windows來架ftp偏偏又不支援utf-8.....結果lftp就亂碼了@@
解法是在登入後輸入:

set ftp:charset "big5"; set file:charset "utf-8"

就可以正確地顯示編碼了！

另外，介紹一下lftp:

登入: lftp user:pwd@site:port or lftp –u user site:port

我常用的指令除了cd 之外就是…mirror了!

mirror [-c 續傳] [-R 把本地mirror上去][-n 只下載新的檔案][-parallel=n 同時傳輸n個檔案] [remote 資料夾] [本地資料夾]

C2DM on Android 2.2

當測試C2DM的時候在Logcat看到這一行"emulatorUnable to start service Intent { act=com.google.android.c2dm.intent.REGISTER (has extras) }: not found"
解法是你的Android Emulator必須是使用Google APIs Add-On的版本!