构建高性能web之路------web服务器长连接

转自： http://blog.csdn.net/cutesource/article/details/5570369
web服务器都提供长连接的方式，所谓长连接就是客户端一次请求完后，不关闭连接，保持一段时间的连接，下次此客户端再次请求时，不用创建新连接，复用所保持的连接即可。从理论上，长连接可以免去大量建立和关闭连接的资源消耗，但同时也有大量连接被占用的代价。因此可以初步判断长连接比短连接能带来更高的TPS，更低的CPU消耗，更少的IO，更高的内存占用，下面通过实战来验证。

服务器环境和测试工具可以见工具和环境准备篇

本次web服务器选用apache prefork模式，apache长短连接的选择可以配置httpd.conf里的KeepAlive选项，如：

KeepAlive On：长连接

KeepAlive Off：短连接

另外如果选择长连接还需配置KeepAliveTimeout和MaxKeepAliveRequests，其中KeepAliveTimeout为每个长连接服务端保持时长，默认配置为15秒，MaxKeepAliveRequests为每个长连接服务请求最大数，默认配置为100次，本次试验保持默认配置。

使用ab来压apache，如：

短连接环境下： /usr/alibaba/install/httpd-2.0.63-prefork/bin/ab -c 100 -n 1000000 http://localhost/
长连接环境下： /usr/alibaba/install/httpd-2.0.63-prefork/bin/ab -c 100 -n 1000000
-k http://localhost/
同时都已100个并发请求apache默认首页1000000次

然后通过ab测试结果、nmon收集资源消耗和strace跟踪实际调用三个维度来考察短连接和长连接的区别。

1）ab测试结果

短连接：

Concurrency Level: 100
Time taken for tests: 190.754776 seconds
Complete requests: 1000000
Failed requests: 0
Write errors: 0
Total transferred: 1891115351 bytes
HTML transferred: 1456088816 bytes
Requests per second: 5242.33 [#/sec] (mean)
Time per request: 19.075 [ms] (mean)
Time per request: 0.191 [ms] (mean, across all concurrent requests)
Transfer rate: 9681.50 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 0 8 3.7 8 44
Processing: 1 10 3.8 9 79
Waiting: 0 7 3.0 7 61
Total: 4 18 5.7 17 101

Concurrency Level:      100
Time taken for tests:   190.754776 seconds
Complete requests:      1000000
Failed requests:        0
Write errors:           0
Total transferred:      1891115351 bytes
HTML transferred:       1456088816 bytes
Requests per second:    5242.33 [#/sec] (mean)
Time per request:       19.075 [ms] (mean)
Time per request:       0.191 [ms] (mean, across all concurrent requests)
Transfer rate:          9681.50 [Kbytes/sec] received
Connection Times (ms)
min  mean[+/-sd] median   max
Connect:        0    8   3.7      8      44
Processing:     1   10   3.8      9      79
Waiting:        0    7   3.0      7      61
Total:          4   18   5.7     17     101

长连接：

Concurrency Level: 100
Time taken for tests: 59.509558 seconds
Complete requests: 1000000
Failed requests: 0
Write errors: 0
Keep-Alive requests: 990148
Total transferred: 1927566346 bytes
HTML transferred: 1456007280 bytes
Requests per second: 16804.02 [#/sec] (mean)
Time per request: 5.951 [ms] (mean)
Time per request: 0.060 [ms] (mean, across all concurrent requests)
Transfer rate: 31631.71 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 0 0 0.1 0 12
Processing: 0 5 22.5 1 1406
Waiting: 0 5 22.4 1 1405
Total: 0 5 22.5 1 1409

Concurrency Level:      100
Time taken for tests:   59.509558 seconds
Complete requests:      1000000
Failed requests:        0
Write errors:           0
Keep-Alive requests:    990148
Total transferred:      1927566346 bytes
HTML transferred:       1456007280 bytes
Requests per second:    16804.02 [#/sec] (mean)
Time per request:       5.951 [ms] (mean)
Time per request:       0.060 [ms] (mean, across all concurrent requests)
Transfer rate:          31631.71 [Kbytes/sec] received
Connection Times (ms)
min  mean[+/-sd] median   max
Connect:        0    0   0.1      0      12
Processing:     0    5  22.5      1    1406
Waiting:        0    5  22.4      1    1405
Total:          0    5  22.5      1    1409

从中不然发现，在其他参数和环境相同的情况下，长连接比短连接的TPS高很多，16804.02/sec vs 5242.33/sec，另外也不难发现长连接在connection上花的时间几乎为0

2）nmon 的测试结果

cpu消耗:

短连接



长连接



以上数据表明长连接比短连接消耗CPU较少

IO占用：

短连接



长连接



以上数据表明长连接比短连接IO占用更少

内存空闲：

短连接



长连接



以上数据表明长连接比短连接占用更多内存

3）strace结果

apache的prefork模式是每个请求由单独的子进程来响应，因此通过对其中的一个子进程跟踪来比较调用系统资源的次数

短连接：

% time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 44.24 0.187941 19 9997 accept 40.22 0.170887 10 17738 poll 2.58 0.010976 0 67716 17737 read 2.49 0.010583 0 59964 9994 lstat 2.19 0.009319 0 49970 9994 stat 1.74 0.007388 0 39976 setsockopt 1.42 0.006045 1 9997 shutdown 1.25 0.005312 0 29988 close 1.06 0.004499 0 19989 open 0.71 0.003003 0 19994 fcntl 0.57 0.002426 0 9994 write 0.45 0.001911 0 9994 writev 0.38 0.001598 0 9994 sendfile 0.35 0.001503 0 9997 getsockname 0.34 0.001439 0 9997 gettimeofday 0.00 0.000002 1 2 fstat 0.00 0.000001 1 1 lseek 0.00 0.000001 1 1 mmap 0.00 0.000001 1 1 munmap ------ ----------- ----------- --------- --------- ---------------- 100.00 0.424835 375310 37725 total

% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
44.24    0.187941          19      9997           accept
40.22    0.170887          10     17738           poll
2.58    0.010976           0     67716     17737 read
2.49    0.010583           0     59964      9994 lstat
2.19    0.009319           0     49970      9994 stat
1.74    0.007388           0     39976           setsockopt
1.42    0.006045           1      9997           shutdown
1.25    0.005312           0     29988           close
1.06    0.004499           0     19989           open
0.71    0.003003           0     19994           fcntl
0.57    0.002426           0      9994           write
0.45    0.001911           0      9994           writev
0.38    0.001598           0      9994           sendfile
0.35    0.001503           0      9997           getsockname
0.34    0.001439           0      9997           gettimeofday
0.00    0.000002           1         2           fstat
0.00    0.000001           1         1           lseek
0.00    0.000001           1         1           mmap
0.00    0.000001           1         1           munmap
------ ----------- ----------- --------- --------- ----------------
100.00    0.424835                375310     37725 total

长连接：

% time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 37.05 0.032997 3 9919 write 21.90 0.019503 2 9940 poll 10.38 0.009248 0 39676 setsockopt 7.86 0.007000 0 49595 9919 stat 7.46 0.006642 0 59514 9919 lstat 5.35 0.004764 0 49720 9941 read 3.54 0.003156 0 19839 open 2.27 0.002018 0 9919 sendfile 1.95 0.001735 0 19941 close 1.28 0.001143 0 9919 writev 0.92 0.000816 0 9921 gettimeofday 0.02 0.000014 0 200 fcntl 0.01 0.000007 0 100 accept 0.01 0.000007 0 100 getsockname 0.01 0.000006 0 100 1 shutdown 0.00 0.000002 1 2 fstat 0.00 0.000001 1 1 lseek 0.00 0.000001 1 1 mmap 0.00 0.000001 1 1 munmap ------ ----------- ----------- --------- --------- ---------------- 100.00 0.089061 288408 29780 total

% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
37.05    0.032997           3      9919           write
21.90    0.019503           2      9940           poll
10.38    0.009248           0     39676           setsockopt
7.86    0.007000           0     49595      9919 stat
7.46    0.006642           0     59514      9919 lstat
5.35    0.004764           0     49720      9941 read
3.54    0.003156           0     19839           open
2.27    0.002018           0      9919           sendfile
1.95    0.001735           0     19941           close
1.28    0.001143           0      9919           writev
0.92    0.000816           0      9921           gettimeofday
0.02    0.000014           0       200           fcntl
0.01    0.000007           0       100           accept
0.01    0.000007           0       100           getsockname
0.01    0.000006           0       100         1 shutdown
0.00    0.000002           1         2           fstat
0.00    0.000001           1         1           lseek
0.00    0.000001           1         1           mmap
0.00    0.000001           1         1           munmap
------ ----------- ----------- --------- --------- ----------------
100.00    0.089061                288408     29780 total

以上数据表明，长连接accept和shutdown次数仅为100次，而短连接为9997次，近100倍的差距，从这里就不难发现为什么长连接的TPS那么高了，省了这么多次系统调用，不快才怪啊。

本次试验得出验证来开始的理论分析：长连接比短连接能带来更高的TPS，更低的CPU消耗，更少的IO，更高的内存占用，更少的系统调用