From 50e9dc01436854bb31ed1187dbfd5c8054b4e6c3 Mon Sep 17 00:00:00 2001
From: mmusich <marco.musich@cern.ch>
Date: Fri, 18 Oct 2024 22:58:53 +0200
Subject: [PATCH] make AlcaBeamMonitor hoard less memory, use a dedicated
 struct instead of storing raw vertices

---
 DQM/BeamMonitor/plugins/AlcaBeamMonitor.cc | 45 ++++++++++++----------
 DQM/BeamMonitor/plugins/AlcaBeamMonitor.h  | 20 +++++++++-
 2 files changed, 43 insertions(+), 22 deletions(-)

diff --git a/DQM/BeamMonitor/plugins/AlcaBeamMonitor.cc b/DQM/BeamMonitor/plugins/AlcaBeamMonitor.cc
index efdd24ab55848..511aa155b7bae 100644
--- a/DQM/BeamMonitor/plugins/AlcaBeamMonitor.cc
+++ b/DQM/BeamMonitor/plugins/AlcaBeamMonitor.cc
@@ -245,8 +245,8 @@ std::shared_ptr<alcabeammonitor::BeamSpotInfo> AlcaBeamMonitor::globalBeginLumin
     BeamSpot::Point apoint(spotDB->x(), spotDB->y(), spotDB->z());
 
     BeamSpot::CovarianceMatrix matrix;
-    for (int i = 0; i < 7; ++i) {
-      for (int j = 0; j < 7; ++j) {
+    for (int i = 0; i < reco::BeamSpot::dimension; ++i) {
+      for (int j = 0; j < reco::BeamSpot::dimension; ++j) {
         matrix(i, j) = spotDB->covariance(i, j);
       }
     }
@@ -296,7 +296,15 @@ void AlcaBeamMonitor::analyze(const Event& iEvent, const EventSetup& iSetup) {
   //------ Primary Vertices
   Handle<VertexCollection> PVCollection;
   if (iEvent.getByToken(primaryVertexLabel_, PVCollection)) {
-    beamSpotInfo->vertices_.push_back(*PVCollection.product());
+    std::vector<alcabeammonitor::pvPosAndErr> vertices;
+    vertices.reserve(PVCollection->size());
+    for (const auto& pv : *PVCollection.product()) {
+      if (pv.isFake() || pv.tracksSize() < 10)
+        continue;
+      vertices.emplace_back(pv);
+    }
+    vertices.shrink_to_fit();
+    beamSpotInfo->vertices_.emplace_back(std::move(vertices));
   }
 
   if (beamSpotInfo->beamSpotMap_.find("SC") == beamSpotInfo->beamSpotMap_.end()) {
@@ -363,24 +371,19 @@ void AlcaBeamMonitor::globalEndLuminosityBlock(const LuminosityBlock& iLumi, con
       }
     }
     vertexResults.clear();
-    for (vector<VertexCollection>::iterator itPV = beamSpotInfo->vertices_.begin();
-         itPV != beamSpotInfo->vertices_.end();
-         itPV++) {
-      if (!itPV->empty()) {
-        for (VertexCollection::const_iterator pv = itPV->begin(); pv != itPV->end(); pv++) {
-          if (pv->isFake() || pv->tracksSize() < 10)
-            continue;
-          if (*itV == "x") {
-            vertexResults.push_back(pair<double, double>(pv->x(), pv->xError()));
-          } else if (*itV == "y") {
-            vertexResults.push_back(pair<double, double>(pv->y(), pv->yError()));
-          } else if (*itV == "z") {
-            vertexResults.push_back(pair<double, double>(pv->z(), pv->zError()));
-          } else if (*itV != "sigmaX" && *itV != "sigmaY" && *itV != "sigmaZ") {
-            LogInfo("AlcaBeamMonitor") << "The histosMap_ has been built with the name " << *itV
-                                       << " that I can't recognize!";
-            //assert(0);
-          }
+
+    for (const auto& itPV : beamSpotInfo->vertices_) {
+      for (const auto& pv : itPV) {
+        if (*itV == "x") {
+          vertexResults.push_back(pv.xWithError());
+        } else if (*itV == "y") {
+          vertexResults.push_back(pv.yWithError());
+        } else if (*itV == "z") {
+          vertexResults.push_back(pv.zWithError());
+        } else if (*itV != "sigmaX" && *itV != "sigmaY" && *itV != "sigmaZ") {
+          LogInfo("AlcaBeamMonitor") << "The histosMap_ has been built with the name " << *itV
+                                     << " that I can't recognize!";
+          //assert(0);
         }
       }
     }
diff --git a/DQM/BeamMonitor/plugins/AlcaBeamMonitor.h b/DQM/BeamMonitor/plugins/AlcaBeamMonitor.h
index 56fcca62531d5..00fb67fbe0e9a 100644
--- a/DQM/BeamMonitor/plugins/AlcaBeamMonitor.h
+++ b/DQM/BeamMonitor/plugins/AlcaBeamMonitor.h
@@ -8,8 +8,11 @@
  */
 // C++
 #include <map>
+#include <array>
 #include <vector>
 #include <string>
+#include <utility>
+
 // CMS
 #include "FWCore/Framework/interface/Frameworkfwd.h"
 #include "FWCore/Framework/interface/Event.h"
@@ -28,8 +31,23 @@ class BeamFitter;
 class PVFitter;
 
 namespace alcabeammonitor {
+
+  struct pvPosAndErr {
+    // Array of pairs: (value, error) for x, y, z
+    std::array<std::pair<double, double>, 3> data;
+
+    // Constructor initializes the array with values and errors from a reco::Vertex
+    pvPosAndErr(const reco::Vertex& vertex)
+        : data{{{vertex.x(), vertex.xError()}, {vertex.y(), vertex.yError()}, {vertex.z(), vertex.zError()}}} {}
+
+    // Accessor functions that return pairs (value, error) directly
+    std::pair<double, double> xWithError() const { return data[0]; }
+    std::pair<double, double> yWithError() const { return data[1]; }
+    std::pair<double, double> zWithError() const { return data[2]; }
+  };
+
   struct BeamSpotInfo {
-    std::vector<reco::VertexCollection> vertices_;
+    std::vector<std::vector<pvPosAndErr>> vertices_;
     typedef std::map<std::string, reco::BeamSpot> BeamSpotContainer;
     BeamSpotContainer beamSpotMap_;
   };