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MXS-1777 MXS-1777 ResponseStat improvements (take 2).

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Fix comments.
Fix a bug in make_valid().
Change sync time (when the average should be pushed to the server EMA)
to only depend on time, not use sample_max. This decreases the amount of
sync calls, and allows for a much shorter sync time. Testing shows this to be
more stabel and allows to make sample_max adaptive .
This commit is contained in:
Niclas Antti 2018-10-03 17:29:35 +03:00
parent 0ff72c5d5e
commit 415c7fa2d7
2 changed files with 14 additions and 24 deletions
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29
include/maxscale/response_stat.hh
View File

@ -16,42 +16,33 @@
#include <maxbase/stopwatch.hh>
#include <maxbase/average.hh>
/** This could arguably be a utility, but is written specifically for rwsplit
* so it stays here at least for now.
*/
namespace maxscale
{
/**
* Query response statistics. Uses median of N samples to filter noise, then
* uses those medians to calculate the average response time.
* The class makes an average of the durations between calls to query_started()
* and query_ended(). Once the stats are good, sync_time_reached(int max) returns true,
* based on the average containing at least max samples (or medians), or the time
* sync_duration (constructor arg) has passed since the last reset().
* Query response time average for a backend. Uses median of N samples to filter noise,
* then uses those medians to calculate the average response time.
*/
class ResponseStat
{
public:
/*
* @param num_filter_samples - collect num samples, use median
* @param num_synch_medians - this many medians before the average should be synced, or
* @param sync_duration - this much time between syncs.
* @param num_filter_samples - collect num samples, use median (digital filter)
* @param sync_duration - this much time between synchronize to server stats.
*/
ResponseStat(int num_filter_samples = 5,
int num_synch_medians = 500,
maxbase::Duration sync_duration = std::chrono::seconds(5));
ResponseStat(int num_filter_samples = 9,
maxbase::Duration sync_duration = std::chrono::milliseconds(250));
void query_started();
void query_ended();// ok to call without a query_started
bool make_valid(); // make valid even if there are too few filter_samples
void query_ended(); // ok to call without a query_started
bool make_valid(); // make valid even if there are only filter_samples
bool is_valid() const;
int num_samples() const;
maxbase::Duration average() const;
bool sync_time_reached(); // is it time to apply the average?
bool sync_time_reached(); // is it time to apply the average to the server?
void reset();
private:
const int m_num_filter_samples;
const int m_num_synch_medians;
const maxbase::Duration m_sync_duration;
int m_sample_count;
std::vector<maxbase::Duration> m_samples; // N sampels from which median is used

9
server/core/response_stat.cc
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@ -17,10 +17,8 @@
namespace maxscale
{
ResponseStat::ResponseStat(int num_filter_samples,
int num_synch_medians,
maxbase::Duration sync_duration)
: m_num_filter_samples {num_filter_samples}
, m_num_synch_medians{num_synch_medians}
, m_sync_duration{sync_duration}
, m_sample_count{0}
, m_samples(num_filter_samples)
@ -39,7 +37,7 @@ void ResponseStat::query_ended()
{
if (m_last_start == maxbase::TimePoint())
{
// m_last_start is defaulted. Ignore, avoids extra logic in call sites.
// m_last_start is defaulted. Ignore, avoids extra logic at call sites.
return;
}
m_samples[m_sample_count] = maxbase::Clock::now() - m_last_start;
@ -58,9 +56,11 @@ bool ResponseStat::make_valid()
{
if (!m_average.num_samples() && m_sample_count)
{
std::sort(m_samples.begin(), m_samples.begin() + m_sample_count);
maxbase::Duration new_sample = m_samples[m_sample_count / 2];
m_average.add(std::chrono::duration<double>(new_sample).count());
m_sample_count = 0;
m_last_start = maxbase::TimePoint();
}
return is_valid();
@ -84,8 +84,7 @@ maxbase::Duration ResponseStat::average() const
bool ResponseStat::sync_time_reached()
{
auto now = maxbase::Clock::now();
bool reached = m_next_sync < now
|| m_average.num_samples() >= m_num_synch_medians;
bool reached = m_next_sync < now;
if (reached)
{