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MXS-1777 Make "Sample Max" of the server EMAverage adaptive

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A rather simple but very effective method as testing shows.
This commit is contained in:
Niclas Antti 2018-10-03 19:05:31 +03:00
parent 19f8e1697b
commit e56492c23f
2 changed files with 34 additions and 8 deletions
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9
server/core/internal/server.hh
View File

@ -47,18 +47,11 @@ public:
return m_response_time.average();
}
void response_time_add(double ave, int num_samples)
{
m_response_time.add(ave, num_samples);
}
void response_time_add(double ave, int num_samples);
mutable std::mutex m_lock;
private:
// nantti, TODO. Decide whether to expose some of this in config, or if the values
// can be calculated at runtime. The "500" or sample_max affects how often a
// session should updates this stat. sample_max should be slightly lower than max sample
// rate (which is less than qps due to the noise filter).
maxbase::EMAverage m_response_time;
};

33
server/core/server.cc
View File

@ -1560,3 +1560,36 @@ double server_response_time_average(const SERVER* srv)
const Server* server = static_cast<const Server*>(srv);
return server->response_time_average();
}
/** Apply backend average and adjust sample_max, which determines the weight of a new average
* applied to EMAverage.
* Sample max is raised if the server is fast, aggresively lowered if the incoming average is clearly
* lower than the EMA, else just lowered a bit. The normal increase and decrease, drifting, of the max
* is done to follow the speed of a server. The important part is the lowering of max, to allow for a
* server that is speeding up to be adjusted and used.
*
* Three new magic numbers to replace the sample max magic number...
*
*/
void Server::response_time_add(double ave, int num_samples)
{
constexpr double drift {1.1};
int current_max = m_response_time.sample_max();
int new_max {0};
if (num_samples >= current_max)
{
new_max = num_samples * drift;
}
else if (m_response_time.average() / ave > 2)
{
new_max = current_max * 0.5;
}
else
{
new_max = current_max / drift;
}
m_response_time.set_sample_max(new_max);
m_response_time.add(ave, num_samples);
}