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misc_services: Fix cache hitrate update

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This patch avoids unncessary CACHE_HITRATES updates through gossip.

After this patch:

Publish CACHE_HITRATES in case:

- We haven't published it at all
- The diff is bigger than 1% and we haven't published in the last 5 seconds
- The diff is really big 10%

Note: A peer node can know the cache hitrate through read_data
read_mutation_data and read_digest RPC verbs which have cache_temperature in
the response. So there is no need to update CACHE_HITRATES through gossip in
high frequency.

We do the recalculation faster if the diff is bigger than 0.01. It is useful to
do the calculation even if we do not publish the CACHE_HITRATES though gossip,
since the recalculation will call the table->set_global_cache_hit_rate to set
the hitrate.

Fixes #5971

Closes #11079
This commit is contained in:
Asias He
2022-07-20 08:52:18 +08:00
committed by Nadav Har'El
parent 5faf3c711d
commit 39db15d2cb
2 changed files with 34 additions and 8 deletions
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2
service/cache_hitrate_calculator.hh
View File

@@ -38,6 +38,8 @@ class cache_hitrate_calculator : public seastar::async_sharded_service<cache_hit
std::unordered_map<utils::UUID, stat> _rates;
size_t _slen = 0;
std::string _gstate;
uint64_t _published_nr = 0;
lowres_clock::time_point _published_time;
future<> _done = make_ready_future();
future<lowres_clock::duration> recalculate_hitrates();

40
service/misc_services.cc
View File

@@ -184,14 +184,38 @@ future<lowres_clock::duration> cache_hitrate_calculator::recalculate_hitrates()
}).then([this] {
_slen = _gstate.size();
using namespace std::chrono_literals;
return _gossiper.add_local_application_state(gms::application_state::CACHE_HITRATES, gms::versioned_value::cache_hitrates(_gstate)).then([this] {
// if max difference during this round is big schedule next recalculate earlier
if (_diff < 0.01) {
return lowres_clock::duration(2000ms);
} else {
return lowres_clock::duration(500ms);
}
});
auto now = lowres_clock::now();
// Publish CACHE_HITRATES in case:
//
// - We haven't published it at all
// - The diff is bigger than 1% and we haven't published in the last 5 seconds
// - The diff is really big 10%
//
// Note: A peer node can know the cache hitrate through read_data
// read_mutation_data and read_digest RPC verbs which have
// cache_temperature in the response. So there is no need to update
// CACHE_HITRATES through gossip in high frequency.
bool do_publish = (_published_nr == 0) ||
(_diff > 0.1) ||
( _diff > 0.01 && (now - _published_time) > 5000ms);
// We do the recalculation faster if the diff is bigger than 0.01. It
// is useful to do the calculation even if we do not publish the
// CACHE_HITRATES though gossip, since the recalculation will call the
// table->set_global_cache_hit_rate to set the hitrate.
auto recalculate_duration = _diff > 0.01 ? lowres_clock::duration(500ms) : lowres_clock::duration(2000ms);
if (do_publish) {
llogger.debug("Send CACHE_HITRATES update max_diff={}, published_nr={}", _diff, _published_nr);
++_published_nr;
_published_time = now;
return _gossiper.add_local_application_state(gms::application_state::CACHE_HITRATES,
gms::versioned_value::cache_hitrates(_gstate)).then([this, recalculate_duration] {
return recalculate_duration;
});
} else {
llogger.debug("Skip CACHE_HITRATES update max_diff={}, published_nr={}", _diff, _published_nr);
return make_ready_future<lowres_clock::duration>(recalculate_duration);
}
}).finally([this] {
_gstate = std::string(); // free memory, do not trust clear() to do that for string
_rates.clear();