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MXS-1777: Initial version of routing based on query response time.

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The main piece of code, slave selection (backend_cmp_response_time), uses the available
method of pair-wise comparison of slaves. This will be changed to selection using all
available slaves, along with removal of hard coded values.
This commit is contained in:
Niclas Antti
2018-07-27 13:07:18 +03:00
parent 1e6509423a
commit 6351ab9c73
10 changed files with 250 additions and 10 deletions
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44
server/modules/routing/readwritesplit/rwsplit_select_backends.cc
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@ -18,7 +18,9 @@
#include <string.h>
#include <stdlib.h>
#include <stdint.h>
#include <sstream>
#include <maxbase/stopwatch.hh>
#include <maxscale/router.h>
using namespace maxscale;
@ -179,6 +181,34 @@ static int backend_cmp_current_load(const SRWBackend& a, const SRWBackend& b)
((1000 + 1000 * second->server->stats.n_current_ops) / second->weight);
}
/** nantti. TODO. TEMP, this needs to see all eligible servers at the same time.
*/
static int backend_cmp_response_time(const SRWBackend& a, const SRWBackend& b)
{
// Minimum average response time for use in selection. Avoids special cases (zero),
// and new servers immediately get some traffic.
constexpr double min_average = 100.0/1000000000; // 100 nano seconds
// Invert the response times.
double lhs = 1/std::max(min_average, a->backend()->server->response_time->average());
double rhs = 1/std::max(min_average, b->backend()->server->response_time->average());
// Clamp values to a range where the slowest is at least some fraction of the speed of the
// fastest. This allows sampling of slaves that have experienced anomalies. Also, if one
// slave is really slow compared to another, something is wrong and perhaps we should
// log something informational.
constexpr int clamp = 20;
double fastest = std::max(lhs, rhs);
lhs = std::max(lhs, fastest / clamp);
rhs = std::max(rhs, fastest / clamp);
// If random numbers are too slow to generate, an array of, say 500'000
// random numbers in the range [0.0, 1.0] could be generated during startup.
double r = rand() / static_cast<double>(RAND_MAX);
return (r < (lhs / (lhs + rhs))) ? -1 : 1;
}
/**
* The order of functions _must_ match with the order the select criteria are
* listed in select_criteria_t definition in readwritesplit.h
@ -189,7 +219,8 @@ int (*criteria_cmpfun[LAST_CRITERIA])(const SRWBackend&, const SRWBackend&) =
backend_cmp_global_conn,
backend_cmp_router_conn,
backend_cmp_behind_master,
backend_cmp_current_load
backend_cmp_current_load,
backend_cmp_response_time
};
/**
@ -234,6 +265,17 @@ static void log_server_connections(select_criteria_t criteria, const SRWBackendL
b->server->port, STRSRVSTATUS(b->server));
break;
case LOWEST_RESPONSE_TIME:
{
maxbase::Duration response_ave(b->server->response_time->average());
std::ostringstream os;
os << response_ave;
MXS_INFO("Average response time : %s from \t[%s]:%d %s",
os.str().c_str(), b->server->address,
b->server->port, STRSRVSTATUS(b->server));
}
break;
default:
mxb_assert(!true);
break;