CouchDB/MochiWeb:持久连接的负面影响

Question

我在Mint/Debian盒子上设置了非常简单的CouchDB.我的Java webapp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:查询模式是许多小查询和小JSON对象(如300字节向上/ 1Kbyte向下).

Wireshark转储非常好,主要显示3-5毫秒的请求 - 响应周转.JVM帧采样向我展示了套接字代码(客户端查询到Couch)有点繁忙,但没什么了不起的.然后我尝试用ApacheBench和oops来描述它:我目前看到keep-alive在非持久性设置上引入了稳定的额外39ms延迟.

有谁知道如何解释这个？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/响应大小而空闲,或类似的东西？是否应该为环回tcp连接打开此选项(TCP_WAIT)？

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"}

保持活着,每次请求平均40毫升

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keepalive,并且瞧 - 每个请求大约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)

好的,现在保持活动状态,但也要求通过http标头关闭连接.每个请求大约1毫秒左右.

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)

Answer 1

是的,这与tcp套接字设置选项有关.现在,这种配置平稳了所有三种情况,每个请求1ms.

[httpd]
socket_options = [{nodelay, true}]

有关详细信息,请参阅此处:http: //wiki.apache.org/couchdb/Performance#Network