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Posted to dev@brpc.apache.org by GitBox <gi...@apache.org> on 2019/12/29 10:46:40 UTC
[GitHub] [incubator-brpc] yanglimingcn opened a new issue #1006: auto
concurrency limiter
yanglimingcn opened a new issue #1006: auto concurrency limiter
URL: https://github.com/apache/incubator-brpc/issues/1006
**Describe the bug (描述bug)**
目前对auto_concurrency_limiter这块的实现遇到些问题，想在这里问一下。现象就是我的服务的latency大概是25us，qps是10000/s,
计算出来的concurrency小于1，导致服务请求都不成功。
自适应算法的公式为：next_max_concurrency = _min_latency_us * _ema_max_qps / 1000000 * (1 + XXX_ratio)
（这里先忽略_explore_ratio 或者 reduce_ratio）
我举个例子说明问题：
1、qps = 10000/s latency = 2500us concurrency = 25
2、qps = 10000/s latency = 25us concurrency = 0.25
直观上看这个latency小的concurrency也小，这个很难理解。
换个角度说一下就是，上面两组数据使用这个公式计算的concurrency 1）代表在2500us时间段内处理25个请求，2）代表在25us时间段内处理0.25个请求。
其实在2500us时间段内2）也能处理25个请求，并且它的qps探索空间应该能更大。但是现在的值是0.25，导致max_concurrency的值一直是0（concurrency是整形），并且恢复不了（因为所有请求都被拒绝了）。
目前的实现有一定的局限性。
**To Reproduce (复现方法)**
auto_concurrency_limiter例子里面的echo处理每个请求的延时修改为25us
**Expected behavior (期望行为)**
能适用到各种数据范围，产生正确的结果。
**Versions (各种版本)**
OS: debian
Compiler:
g++ (Debian 4.9.2-10+deb8u1) 4.9.2
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
brpc: master
protobuf:
**Additional context/screenshots (更多上下文/截图)**
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[GitHub] [incubator-brpc] zyearn commented on issue #1006: auto concurrency
limiter
Posted by GitBox <gi...@apache.org>.
zyearn commented on issue #1006: auto concurrency limiter
URL: https://github.com/apache/incubator-brpc/issues/1006#issuecomment-570985514
little's law说的就是long-term average，均值稳定就可以
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[GitHub] [incubator-brpc] yanglimingcn commented on issue #1006: auto
concurrency limiter
Posted by GitBox <gi...@apache.org>.
yanglimingcn commented on issue #1006: auto concurrency limiter
URL: https://github.com/apache/incubator-brpc/issues/1006#issuecomment-570181153
再请教个问题，是不是服务的请求执行时间不是很稳定的服务不太适合这个算法啊？的确根据little‘s law的理论，得到并发度，但是我测试发现，相比最小latency，我放宽一些latency，qps就高起来了。
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[GitHub] [incubator-brpc] zyearn commented on issue #1006: auto concurrency
limiter
Posted by GitBox <gi...@apache.org>.
zyearn commented on issue #1006: auto concurrency limiter
URL: https://github.com/apache/incubator-brpc/issues/1006#issuecomment-569686934
latency qps和 concurrency满足[little's law](https://en.wikipedia.org/wiki/Little%27s_law)，也是目前这套自适应限流的理论基础。你说的concurrency小于1的问题应该在https://github.com/apache/incubator-brpc/pull/1003 要修复的问题
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[GitHub] [incubator-brpc] zyearn edited a comment on issue #1006: auto
concurrency limiter
Posted by GitBox <gi...@apache.org>.
zyearn edited a comment on issue #1006: auto concurrency limiter
URL: https://github.com/apache/incubator-brpc/issues/1006#issuecomment-569686934
latency qps和 concurrency满足[little's law](https://en.wikipedia.org/wiki/Little%27s_law)，也是目前这套自适应限流的理论基础。你说的concurrency小于1的问题应该是 https://github.com/apache/incubator-brpc/pull/1003 要修复的问题
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