Show every group w.r.t. an object when an object belongs to multiple groups in the same partition

Summary:
The object table currently shows only one group when an object belongs to multiple groups in an overlapping partition. [[https://www.internalfb.com/code/fbsource/[573d17b48f]/fbcode/rebalancer/explorer/cpp_server/lib/LoadModel.cpp?lines=138-160 | The partition column overwrites the object's group name]] as it visits each group, so only the last group remains.

In this diff, [[https://www.internalfb.com/code/fbsource/[00b5e442e4cc]/fbcode/rebalancer/explorer/cpp_server/lib/LoadModel.cpp?lines=138-166 | disjoint partitions keep their existing construction, while overlapping partitions collect, sort, and join every group name]]. Objects in one group and objects outside the partition keep their existing output.

Reviewed By: sud03r

Differential Revision: D116634650

fbshipit-source-id: 62be80852f27ab38fb9e9314e15640c06d271577

Author: vj-menon

algopt/rebalancer/explorer/cpp_server/lib/LoadModel.cpp

@@ -21,6 +21,7 @@
 #include <fmt/core.h>
 #include <folly/FileUtil.h>
 #include <folly/futures/SharedPromise.h>
+#include <folly/String.h>
 #include <folly/Synchronized.h>
 #include <folly/system/HardwareConcurrency.h>
 
@@ -138,11 +139,19 @@ static std::vector<std::shared_ptr<const Column>> buildPartitionCols(
     auto& partition = universe.getPartition(partitionId);
     auto& partitionName = universe.getEntityName(partitionId);
     Map<EntityId, DataCell> objectToCell;
-    for (auto groupId : partition.getGroupIds()) {
-      auto& groupName = universe.getEntityName(groupId);
-      for (auto objectId : partition.getObjectIds(groupId)) {
-        const DataCell name(groupName);
-        objectToCell[toEntityId(objectId)] = name;
+    for (const auto& [objectId, groupIds] : partition.getObjectIdToGroupIds()) {
+      if (groupIds.size() == 1) {
+        objectToCell[toEntityId(objectId)] =
+            DataCell(universe.getEntityName(groupIds.front()));
+      } else {
+        std::vector<std::string> groupNames;
+        groupNames.reserve(groupIds.size());
+        for (const auto groupId : groupIds) {
+          groupNames.push_back(universe.getEntityName(groupId));
+        }
+        std::sort(groupNames.begin(), groupNames.end());
+        objectToCell[toEntityId(objectId)] =
+            DataCell(folly::join(", ", groupNames));
       }
     }
     DataCell defaultPartition("");

algopt/rebalancer/explorer/cpp_server/tests/LoadModelTest.cpp

@@ -311,6 +311,26 @@ TEST(LoadModelTest, Basic) {
   }
 }
 
+TEST(LoadModelTest, OverlappingPartitionJoinsGroups) {
+  auto bundle = TestUtils::buildBundle({.includeOverlappedPartition = true});
+  auto explorerModel = LoadModel::buildData(std::move(bundle));
+  addObjectTable(explorerModel);
+
+  const auto& universe = *explorerModel.universe;
+  const auto& table = explorerModel.tableData.at("host");
+  const auto partitionColumn =
+      Utils::fetchColumn(table.getColumnData(), "overlapped");
+  EXPECT_EQ(
+      "group1, group2",
+      partitionColumn->getStrView(toEntityId(universe.getObjectId("host0"))));
+  EXPECT_EQ(
+      "group1",
+      partitionColumn->getStrView(toEntityId(universe.getObjectId("host3"))));
+  EXPECT_EQ(
+      "",
+      partitionColumn->getStrView(toEntityId(universe.getObjectId("host4"))));
+}
+
 TEST(LoadModelTest, DynamicDimensionTableUsesGroupRowsForCompactStorage) {
   UniverseProblemBuilder builder(
       std::make_unique<AsyncConfig>(getTestExecutor(/*numThreads=*/true)));