我在我的Mint/Debian机器上安装了CouchDB。我的Java Web应用程序在查询CouchDB时遇到了相当长的延迟，所以我开始寻找原因。
编辑：查询模式是很多小查询和小JSON对象（如300字节/1K字节）。Wireshark转储非常好，显示大多数请求-响应时间为3-5毫秒。JVM帧采样向我展示套接字代码（客户端对Couch的查询）有些繁忙，但没有什么值得注意的地方。然后我尝试使用ApacheBench进行相同的分析，结果出乎意料：我发现保持连接会比非持久设置多稳定的39ms延迟。
有人知道如何解释这个问题吗？也许持久连接会增加TCP层的拥塞窗口，然后由于TCP_WAIT和小的请求/响应大小而处于空闲状态，或者类似的情况？这个选项（TCP_WAIT）是否应该对环回tcp连接启用？
没有保持连接，然后就出现了 - 每个请求平均1毫秒。
有人知道如何解释这个问题吗？也许持久连接会增加TCP层的拥塞窗口，然后由于TCP_WAIT和小的请求/响应大小而处于空闲状态，或者类似的情况？这个选项（TCP_WAIT）是否应该对环回tcp连接启用？
w@mint ~ $ uname -a
Linux mint 2.6.39-2-486 #1 Tue Jul 5 02:52:23 UTC 2011 i686 GNU/Linux
w@mint ~ $ curl http://127.0.0.1:5984/
{"couchdb":"Welcome","version":"1.1.1"}
保持连接运行，平均每个请求40毫秒
w@mint ~ $ ab -n 1024 -c 1 -k http://127.0.0.1:5984/
>>>snip
Server Software: CouchDB/1.1.1
Server Hostname: 127.0.0.1
Server Port: 5984
Document Path: /
Document Length: 40 bytes
Concurrency Level: 1
Time taken for tests: 41.001 seconds
Complete requests: 1024
Failed requests: 0
Write errors: 0
Keep-Alive requests: 1024
Total transferred: 261120 bytes
HTML transferred: 40960 bytes
Requests per second: 24.98 [#/sec] (mean)
Time per request: 40.040 [ms] (mean)
Time per request: 40.040 [ms] (mean, across all concurrent requests)
Transfer rate: 6.22 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 0 0 0.0 0 0
Processing: 1 40 1.4 40 48
Waiting: 0 1 0.7 1 8
Total: 1 40 1.3 40 48
Percentage of the requests served within a certain time (ms)
50% 40
>>>snip
95% 40
98% 41
99% 44
100% 48 (longest request)
没有保持连接，然后就出现了 - 每个请求平均1毫秒。
w@mint ~ $ ab -n 1024 -c 1 http://127.0.0.1:5984/
>>>snip
Time taken for tests: 1.080 seconds
Complete requests: 1024
Failed requests: 0
Write errors: 0
Total transferred: 236544 bytes
HTML transferred: 40960 bytes
Requests per second: 948.15 [#/sec] (mean)
Time per request: 1.055 [ms] (mean)
Time per request: 1.055 [ms] (mean, across all concurrent requests)
Transfer rate: 213.89 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 0 0 0.0 0 0
Processing: 1 1 1.0 1 11
Waiting: 1 1 0.9 1 11
Total: 1 1 1.0 1 11
Percentage of the requests served within a certain time (ms)
50% 1
>>>snip
80% 1
90% 2
95% 3
98% 5
99% 6
100% 11 (longest request)
现在，我们开启了keep-alive并通过http头部请求关闭连接。每个请求大约需要1毫秒的时间。
w@mint ~ $ ab -n 1024 -c 1 -k -H 'Connection: close' http://127.0.0.1:5984/
>>>snip
Time taken for tests: 1.131 seconds
Complete requests: 1024
Failed requests: 0
Write errors: 0
Keep-Alive requests: 0
Total transferred: 236544 bytes
HTML transferred: 40960 bytes
Requests per second: 905.03 [#/sec] (mean)
Time per request: 1.105 [ms] (mean)
Time per request: 1.105 [ms] (mean, across all concurrent requests)
Transfer rate: 204.16 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 0 0 0.0 0 0
Processing: 1 1 1.2 1 14
Waiting: 0 1 1.1 1 13
Total: 1 1 1.2 1 14
Percentage of the requests served within a certain time (ms)
50% 1
>>>snip
80% 1
90% 2
95% 3
98% 6
99% 7
100% 14 (longest request)
nodelay，但我不确定是否正确以及如何确认它。 - JasonSmith