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Avoid large alloc in prometheus metrics with unordered_dense #104

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Avoid large alloc in prometheus metrics with unordered_dense #104

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ed9d967
cmake: add unordered_dense dependency
ballard26 Apr 5, 2024
7fc06e4
core: switch from std::unordered_map to ankerl::unordered_dense::segm…
ballard26 Apr 5, 2024
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1 change: 1 addition & 0 deletions CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -798,6 +798,7 @@ target_link_libraries (seastar
lksctp-tools::lksctp-tools
rt::rt
yaml-cpp::yaml-cpp
unordered_dense::unordered_dense
"$<BUILD_INTERFACE:Valgrind::valgrind>"
Threads::Threads)

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5 changes: 4 additions & 1 deletion cmake/SeastarDependencies.cmake
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Expand Up @@ -103,7 +103,8 @@ macro (seastar_find_dependencies)
lksctp-tools # No version information published.
numactl # No version information published.
rt
yaml-cpp)
yaml-cpp
unordered_dense)

# Arguments to `find_package` for each 3rd-party dependency.
# Note that the version specification is a "minimal" version requirement.
Expand Down Expand Up @@ -143,6 +144,8 @@ macro (seastar_find_dependencies)
OPTION ${Seastar_NUMA})
seastar_set_dep_args (yaml-cpp REQUIRED
VERSION 0.5.1)
seastar_set_dep_args (unordered_dense
VERSION 4.4.0 CONFIG REQUIRED)

foreach (third_party ${_seastar_all_dependencies})
if (NOT _seastar_dep_skip_${third_party})
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8 changes: 5 additions & 3 deletions src/core/prometheus.cc
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Expand Up @@ -33,6 +33,8 @@
#include <seastar/core/loop.hh>
#include <regex>

#include <ankerl/unordered_dense.h>

namespace seastar {

extern seastar::logger seastar_logger;
Expand Down Expand Up @@ -531,7 +533,7 @@ void write_summary(std::stringstream& s, const config& ctx, const sstring& name,
*/
class metric_aggregate_by_labels {
std::vector<std::string> _labels_to_aggregate_by;
std::unordered_map<std::map<sstring, sstring>, seastar::metrics::impl::metric_value> _values;
ankerl::unordered_dense::segmented_map<std::map<sstring, sstring>, seastar::metrics::impl::metric_value> _values;
public:
metric_aggregate_by_labels(std::vector<std::string> labels) : _labels_to_aggregate_by(std::move(labels)) {
}
Expand All @@ -548,14 +550,14 @@ class metric_aggregate_by_labels {
for (auto&& l : _labels_to_aggregate_by) {
labels.erase(l);
}
std::unordered_map<std::map<sstring, sstring>, seastar::metrics::impl::metric_value>::iterator i = _values.find(labels);
auto i = _values.find(labels);
if ( i == _values.end()) {
_values.emplace(std::move(labels), m);
} else {
i->second += m;
}
}
const std::unordered_map<std::map<sstring, sstring>, seastar::metrics::impl::metric_value>& get_values() const noexcept {
const auto& get_values() const noexcept {
return _values;
}
bool empty() const noexcept {
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