用ab命令来对 JVM进行内存分析的一个例子之前写在新浪博客里的，转发过来：?关于ab的介绍前面的帖子已经说过
用ab命令来对 JVM进行内存分析的一个例子
之前写在新浪博客里的，转发过来：
?
关于ab的介绍前面的帖子已经说过了。
现在就结合之前讲得JVM内存，用实例来过一遍：
1、JVM的启动参数·我是这样设置的：??java -Xmx1024m -Xms1024m -Xss128k -XX:NewRatio=4 -XX:SurvivorRatio=4 -XX:MaxPermSize=16m
·启动tomcat之后，使用 jmap -heap `pgrep -u root java`，得到如下信息：Heap Configuration:???MinHeapFreeRatio = 40???MaxHeapFreeRatio = 70???MaxHeapSize ?????= 1073741824 (1024.0MB)???NewSize ?????????= 1048576 (1.0MB)???MaxNewSize ??????= 4294901760 (4095.9375MB)???OldSize ?????????= 4194304 (4.0MB)???NewRatio ????????= 4???SurvivorRatio ???= 4???PermSize ????????= 12582912 (12.0MB)???MaxPermSize ?????= 16777216 (16.0MB)
Heap Usage:New Generation (Eden + 1 Survivor Space):???capacity = 178913280 (170.625MB)???used ????= 51533904 (49.14656066894531MB)???free ????= 127379376 (121.47843933105469MB)???28.80384508070055% usedEden Space:???capacity = 143130624 (136.5MB)???used ????= 51533904 (49.14656066894531MB)???free ????= 91596720 (87.35343933105469MB)???36.00480635087569% usedFrom Space:???capacity = 35782656 (34.125MB)???used ????= 0 (0.0MB)???free ????= 35782656 (34.125MB)???0.0% usedTo Space:???capacity = 35782656 (34.125MB)???used ????= 0 (0.0MB)???free ????= 35782656 (34.125MB)???0.0% usedtenured generation:???capacity = 859045888 (819.25MB)???used ????= 1952984 (1.8625106811523438MB)???free ????= 857092904 (817.3874893188477MB)???0.22734338494383202% usedPerm Generation:???capacity = 12582912 (12.0MB)???used ????= 6656024 (6.347679138183594MB)???free ????= 5926888 (5.652320861816406MB)???52.897326151529946% used------------------------------------------华丽的分割线---------------------------------------
按照这个参数来计算的话（可以参考这里：http://blog.sina.com.cn/s/blog_68158ebf0100wp83.html）-Xmx1024m -Xms1024m -Xss128k -XX:NewRatio=4 -XX:SurvivorRatio=4 -XX:MaxPermSize=16m
-Xmx1024m 最大堆内存为 1024M-Xms1024m 初始堆内存为 1024M
-XX:NewRatio=4?则 年轻代:年老代=1:4 ?1024M/5=204.8M故 年轻代=204.8M ?年老代=819.2M
-XX:SurvivorRatio=4则年轻代中 2Survivor:1Eden=2:4 204.8M/6=34.13333333333333M故 Eden=136.5333333333333M ?1Suivivor=34.13333333333333M
用 jmap -heap <pid>查看的结果 与我们计算的结果一致
-----------------------------------华丽的分割线-------------------------------------------
3、编写测试页面????在网站根目录里新建页面perf.jsp，内容如下：<%intsize = (int)(1024 * 1024 * m);byte[] buffer = new byte[size];Thread.sleep(s);%>
注：m值用来设置每次申请内存的大小，s 表示睡眠多少ms
4、使用jstat来监控内存变化·jstat命令的用法和介绍，参考这里http://blog.sina.com.cn/s/blog_68158ebf0100woyh.html
这里使用?jstat -gcutil `pgrep -u root java` 1500 10????再解释一下，这里有三个参数：·pgrep -u root java --> 得到java的进程ID号·1500 --> 表示每隔1500ms取一次数据·10 --> 表示一共取10次数据
5、用ab来进行压测
压测的命令：[root@CentOS ~]#?ab -c150 -n50000 "http://localhost/perf.jsp?m=1&s=10"
注：这里使用150个线程并发访问，一共访问50000次。????另外我做了apache与tomcat的整合，过程见：http://blog.sina.com.cn/s/blog_68158ebf0100wnvx.html默认情况下你可以使用 http://localhost:8080/perf.jsp?m=1&s=10 来访问。
--------------------------------------------华丽的分割线----------------------------------------下面开始进行实验：·先启动Java内存的监听：????[root@CentOS ~]# jstat -gcutil 8570 1500 10?·在开启一个终端，开始压测：????[root@CentOS ~]# ab -c150 -n50000 "http://localhost/perf.jsp?m=1&s=10"
两个命令结束之后的结果如下：·jstat：[root@CentOS ~]# jstat -gcutil 8570 1500 10???S0 ????S1 ????E ?????O ?????P ????YGC ????YGCT ???FGC ???FGCT ????GCT ????0.06 ??0.00 ?53.15 ??2.03 ?67.18 ????52 ???0.830 ????1 ???0.218 ???1.048??0.00 ??0.04 ?18.46 ??2.03 ?67.18 ????55 ???0.833 ????1 ???0.218 ???1.052??0.03 ??0.00 ?28.94 ??2.03 ?67.18 ????56 ???0.835 ????1 ???0.218 ???1.053??0.00 ??0.04 ?34.02 ??2.03 ?67.18 ????57 ???0.836 ????1 ???0.218 ???1.054??0.04 ??0.00 ?34.13 ??2.03 ?67.18 ????58 ???0.837 ????1 ???0.218 ???1.055??0.00 ??0.04 ?38.62 ??2.03 ?67.18 ????59 ???0.838 ????1 ???0.218 ???1.056??0.04 ??0.00 ??8.39 ??2.03 ?67.18 ????60 ???0.839 ????1 ???0.218 ???1.058??0.04 ??0.00 ??8.39 ??2.03 ?67.18 ????60 ???0.839 ????1 ???0.218 ???1.058??0.04 ??0.00 ??8.39 ??2.03 ?67.18 ????60 ???0.839 ????1 ???0.218 ???1.058??0.04 ??0.00 ??8.39 ??2.03 ?67.18 ????60 ???0.839 ????1 ???0.218 ???1.058
结果简单解析：????可以看到JVM里S0和S1始终有一个是空的，Eden区达到一定比例之后就会产生Minor GC，由于我这里的Old Generation 区设置的比较大，所以没有产生Full GC。
·ab[root@CentOS ~]# ab -c150 -n50000 "http://localhost/perf.jsp?m=1&s=10"
This is ApacheBench, Version 2.0.40-dev <$Revision: 1.146 $> apache-2.0Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/Copyright 2006 The Apache Software Foundation, http://www.apache.org/
Benchmarking localhost (be patient)Completed 5000 requestsCompleted 10000 requestsCompleted 15000 requestsCompleted 20000 requestsCompleted 25000 requestsCompleted 30000 requestsCompleted 35000 requestsCompleted 40000 requestsCompleted 45000 requestsFinished 50000 requests
Server Software: ???????Apache/2.2.3Server Hostname: ???????localhostServer Port: ???????????80
Document Path: ?????????/perf.jsp?m=1&s=10Document Length: ???????979 bytes
Concurrency Level: ?????150Time taken for tests: ??13.467648 secondsComplete requests: ?????50000Failed requests: ???????0Write errors: ??????????0Non-2xx responses: ?????50005Total transferred: ?????57605760 bytesHTML transferred: ??????48954895 bytesRequests per second: ???3712.60 [#/sec] (mean)Time per request: ??????40.403 [ms] (mean) ??#平均请求时间Time per request: ??????0.269 [ms] (mean, across all concurrent requests)?Transfer rate: ?????????4177.05 [Kbytes/sec] received
Connection Times (ms)??????????????min ?mean[+/-sd] median ??maxConnect: ???????0 ???1 ?46.5 ?????0 ???3701Processing: ???10 ??38 ?70.3 ????36 ???6885Waiting: ???????3 ??35 ?70.3 ????33 ???6883Total: ????????10 ??39 ?84.4 ????37 ???6901
Percentage of the requests served within a certain time (ms)??50% ????37??66% ????38??75% ????39??80% ????39??90% ????41??95% ????43??98% ????50??99% ????58?100% ??6901 (longest request)
详细的分析见：http://blog.sina.com.cn/s/blog_68158ebf0100woyp.html
------------------------------------------华丽的分割线------------------------------------------
全文完。
