[ML] Replace CResourceMonitor::m_AllocationFailures to reduce the memory footprint (#2527)

Fixes #2524

Author: valeriy42

include/model/CResourceMonitor.h

@@ -179,7 +179,6 @@ class MODEL_EXPORT CResourceMonitor {
 private:
     using TMonitoredResourcePtrSizeUMap =
         boost::unordered_map<CMonitoredResource*, std::size_t>;
-    using TTimeSizeMap = std::map<core_t::TTime, std::size_t>;
     using TMeanVarAccumulator =
         maths::common::CBasicStatistics::SSampleMeanVar<double>::TAccumulator;
 
@@ -258,8 +257,11 @@ class MODEL_EXPORT CResourceMonitor {
     //! Callback function to fire when memory usage increases by 1%
     TMemoryUsageReporterFunc m_MemoryUsageReporter;
 
-    //! Keep track of times of anomaly detector allocation failures
-    TTimeSizeMap m_AllocationFailures;
+    //! Keep track of the number of distinct allocation failures
+    std::size_t m_AllocationFailuresCount{0};
+
+    //! The time at which the last allocation failure occurred
+    core_t::TTime m_LastAllocationFailureTime{0};
 
     //! The time at which the last allocation failure was reported
     core_t::TTime m_LastAllocationFailureReport{0};

lib/model/CResourceMonitor.cc

@@ -318,9 +318,8 @@ bool CResourceMonitor::needToSendReport(model_t::EAssignmentMemoryBasis currentA
     }
 
     // Have we had new allocation failures
-    if (!m_AllocationFailures.empty()) {
-        core_t::TTime latestAllocationError{(--m_AllocationFailures.end())->first};
-        if (latestAllocationError > m_LastAllocationFailureReport) {
+    if (m_AllocationFailuresCount != 0) {
+        if (m_LastAllocationFailureTime > m_LastAllocationFailureReport) {
             return true;
         }
     }
@@ -369,8 +368,8 @@ void CResourceMonitor::sendMemoryUsageReport(core_t::TTime bucketStartTime,
         total);
     if (m_MemoryUsageReporter) {
         m_MemoryUsageReporter(this->createMemoryUsageReport(bucketStartTime));
-        if (!m_AllocationFailures.empty()) {
-            m_LastAllocationFailureReport = m_AllocationFailures.rbegin()->first;
+        if (m_AllocationFailuresCount != 0) {
+            m_LastAllocationFailureReport = m_LastAllocationFailureTime;
         }
     }
     m_PreviousTotal = total;
@@ -395,7 +394,7 @@ CResourceMonitor::createMemoryUsageReport(core_t::TTime bucketStartTime) {
     for (const auto& resource : m_Resources) {
         resource.first->updateModelSizeStats(res);
     }
-    res.s_AllocationFailures += m_AllocationFailures.size();
+    res.s_AllocationFailures += m_AllocationFailuresCount;
     res.s_OverallCategorizerStats.s_MemoryCategorizationFailures += m_CategorizerAllocationFailures;
     return res;
 }
@@ -428,7 +427,10 @@ std::size_t CResourceMonitor::persistenceMemoryIncreaseFactor() const {
 
 void CResourceMonitor::acceptAllocationFailureResult(core_t::TTime time) {
     m_MemoryStatus = model_t::E_MemoryStatusHardLimit;
-    ++m_AllocationFailures[time];
+    if (time > m_LastAllocationFailureTime) {
+        m_AllocationFailuresCount += 1;
+        m_LastAllocationFailureTime = time;
+    }
 }
 
 void CResourceMonitor::startPruning() {

lib/model/unittest/CResourceMonitorTest.cc

@@ -341,7 +341,7 @@ BOOST_FIXTURE_TEST_CASE(testMonitor, CTestFixture) {
         mon.acceptAllocationFailureResult(14401000);
         mon.acceptAllocationFailureResult(14402000);
 
-        BOOST_REQUIRE_EQUAL(3, mon.m_AllocationFailures.size());
+        BOOST_REQUIRE_EQUAL(3, mon.m_AllocationFailuresCount);
         BOOST_REQUIRE_EQUAL(core_t::TTime(0), mon.m_LastAllocationFailureReport);
         mon.refresh(categorizer);
         mon.refresh(detector1);