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cache_hitrate_calculator: make cache hitrate calculation preemptable

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The calculation is done in a non preemptable loop over all tables, so if
numbers of tables is very large it may take a while since we also build
a string for gossiper state. Make the loop preemtable and also make
the string calculation more efficient by preallocating memory for it.
Message-Id: <20190516132748.6469-3-gleb@scylladb.com>
This commit is contained in:
Gleb Natapov
2019-05-16 16:27:48 +03:00
committed by Tomasz Grabiec
parent 4517c56a57
commit 31bf4cfb5e
2 changed files with 19 additions and 15 deletions
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2
service/cache_hitrate_calculator.hh
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@@ -46,6 +46,8 @@ class cache_hitrate_calculator : public seastar::async_sharded_service<cache_hit
bool _stopped = false;
float _diff = 0;
std::unordered_map<utils::UUID, stat> _rates;
size_t _slen = 0;
std::string _gstate;
future<> _done = make_ready_future();
future<lowres_clock::duration> recalculate_hitrates();

32
service/misc_services.cc
View File

@@ -134,16 +134,18 @@ future<lowres_clock::duration> cache_hitrate_calculator::recalculate_hitrates()
return _db.map_reduce0(cf_to_cache_hit_stats, std::unordered_map<utils::UUID, stat>(), sum_stats_per_cf).then([this, non_system_filter] (std::unordered_map<utils::UUID, stat> rates) mutable {
_diff = 0;
_gstate.reserve(_slen); // assume length did not change from previous iteration
_slen = 0;
_rates = std::move(rates);
// set calculated rates on all shards
return _db.invoke_on_all([this, cpuid = engine().cpu_id(), non_system_filter] (database& db) {
sstring gstate;
for (auto& cf : db.get_column_families() | boost::adaptors::filtered(non_system_filter)) {
auto it = _rates.find(cf.first);
if (it == _rates.end()) { // a table may be added before map/reduce completes and this code runs
continue;
return do_for_each(_rates, [this, cpuid, &db] (auto&& r) mutable {
auto it = db.get_column_families().find(r.first);
if (it == db.get_column_families().end()) { // a table may be added before map/reduce completes and this code runs
return;
}
stat s = it->second;
auto& cf = *it;
stat& s = r.second;
float rate = 0;
if (s.h) {
rate = s.h / (s.h + s.m);
@@ -151,25 +153,25 @@ future<lowres_clock::duration> cache_hitrate_calculator::recalculate_hitrates()
if (engine().cpu_id() == cpuid) {
// calculate max difference between old rate and new one for all cfs
_diff = std::max(_diff, std::abs(float(cf.second->get_global_cache_hit_rate()) - rate));
gstate += format("{}.{}:{:f};", cf.second->schema()->ks_name(), cf.second->schema()->cf_name(), rate);
_gstate += format("{}.{}:{:0.6f};", cf.second->schema()->ks_name(), cf.second->schema()->cf_name(), rate);
}
cf.second->set_global_cache_hit_rate(cache_temperature(rate));
}
if (gstate.size()) {
auto& g = gms::get_local_gossiper();
auto& ss = get_local_storage_service();
return g.add_local_application_state(gms::application_state::CACHE_HITRATES, ss.value_factory.cache_hitrates(std::move(gstate)));
}
return make_ready_future<>();
});
});
}).then([this] {
_rates.clear();
auto& g = gms::get_local_gossiper();
auto& ss = get_local_storage_service();
_slen = _gstate.size();
g.add_local_application_state(gms::application_state::CACHE_HITRATES, ss.value_factory.cache_hitrates(_gstate));
// if max difference during this round is big schedule next recalculate earlier
if (_diff < 0.01) {
return std::chrono::milliseconds(2000);
} else {
return std::chrono::milliseconds(500);
}
}).finally([this] {
_gstate = std::string(); // free memory, do not trust clear() to do that for string
_rates.clear();
});
}