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MXS-1777 Make sure slower servers are sampled sufficiently

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This commit is contained in:
Niclas Antti
2018-10-03 18:01:34 +03:00
parent 415c7fa2d7
commit ada91f2d53
1 changed files with 15 additions and 5 deletions
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20
server/modules/routing/readwritesplit/rwsplit_select_backends.cc
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@ -109,7 +109,8 @@ SRWBackendVector::iterator backend_cmp_behind_master(SRWBackendVector& sBackends
SRWBackendVector::iterator backend_cmp_current_load(SRWBackendVector& sBackends) SRWBackendVector::iterator backend_cmp_current_load(SRWBackendVector& sBackends)
{ {
static auto server_score = [](SERVER_REF* server) { static auto server_score = [](SERVER_REF* server) {
return server->server_weight ? (server->server->stats.n_current_ops + 1) / server->server_weight : 0; return server->server_weight ? (server->server->stats.n_current_ops + 1)
/ server->server_weight : 0;
}; };
return best_score(sBackends, server_score); return best_score(sBackends, server_score);
@ -122,23 +123,32 @@ SRWBackendVector::iterator backend_cmp_response_time(SRWBackendVector& sBackends
// fill slots with inverses of averages // fill slots with inverses of averages
double total {0}; double total {0};
double fastest {0};
for (int i = 0; i < SZ; ++i) for (int i = 0; i < SZ; ++i)
{ {
SERVER_REF* server = (**sBackends[i]).backend(); SERVER_REF* server = (**sBackends[i]).backend();
auto ave = server_response_time_average(server->server); double ave = server_response_time_average(server->server);
if (ave == 0) if (ave == 0)
{ {
constexpr double very_quick = 1.0 / 10000000; // arbitrary very short duration (0.1 constexpr double very_quick = 1.0 / 10000000; // arbitrary very short duration (0.1 us)
// microseconds)
slot[i] = 1 / very_quick; // will be used and updated (almost) immediately. slot[i] = 1 / very_quick; // will be used and updated (almost) immediately.
} }
else else
{ {
slot[i] = 1 / ave; slot[i] = 1 / ave;
} }
slot[i] = slot[i] * slot[i]; // favor faster servers even more slot[i] = slot[i] * slot[i] * slot[i]; // favor faster servers even more
total += slot[i]; total += slot[i];
fastest = std::max(fastest, slot[i]);
}
// make the slowest server at least a good fraction of the fastest to guarantee
// some amount of sampling, should the slow server become faster.
constexpr int divisor = 200; // 0.5%
for (int i = 0; i < SZ; ++i)
{
slot[i] = std::max(slot[i], fastest / divisor);
} }
// turn slots into a roulette wheel, where sum of slots is 1.0 // turn slots into a roulette wheel, where sum of slots is 1.0