Do not force Sample+Reshuffle on the first level (#19154) (#20132)

Author: vitalif

ydb/core/tx/schemeshard/schemeshard_build_index__progress.cpp

@@ -821,10 +821,6 @@ struct TSchemeShard::TIndexBuilder::TTxProgress: public TSchemeShard::TIndexBuil
 
     void AddGlobalShardsForCurrentParent(TIndexBuildInfo& buildInfo) {
         Y_ENSURE(NoShardsAdded(buildInfo));
-        if (buildInfo.KMeans.Parent == 0) {
-            AddAllShards(buildInfo);
-            return;
-        }
         auto it = buildInfo.Cluster2Shards.lower_bound(buildInfo.KMeans.Parent);
         Y_ENSURE(it != buildInfo.Cluster2Shards.end());
         if (it->second.Shards.size() > 1) {

ydb/core/tx/schemeshard/schemeshard_info_types.cpp

@@ -2215,13 +2215,12 @@ void TIndexBuildInfo::SerializeToProto([[maybe_unused]] TSchemeShard* ss, NKikim
 }
 
 void TIndexBuildInfo::AddParent(const TSerializedTableRange& range, TShardIdx shard) {
-    if (KMeans.Parent == 0) {
-        // For Parent == 0 only single kmeans needed, so there is only two options:
-        // 1. It fits entirely in the single shard => local kmeans for single shard
-        // 2. It doesn't fit entirely in the single shard => global kmeans for all shards
-        return;
-    }
-    const auto [parentFrom, parentTo] = KMeans.RangeToBorders(range);
+    // For Parent == 0 only single kmeans needed, so there are two options:
+    // 1. It fits entirely in the single shard => local kmeans for single shard
+    // 2. It doesn't fit entirely in the single shard => global kmeans for all shards
+    const auto [parentFrom, parentTo] = KMeans.Parent == 0
+        ? std::pair<NTableIndex::TClusterId, NTableIndex::TClusterId>{0, 0}
+        : KMeans.RangeToBorders(range);
     // TODO(mbkkt) We can make it more granular
 
     // the new range does not intersect with other ranges, just add it with 1 shard

ydb/core/tx/schemeshard/ut_index_build/ut_vector_index_build.cpp

@@ -387,11 +387,10 @@ Y_UNIT_TEST_SUITE (VectorIndexBuildTest) {
         }
 
         // Wait and check Filling state:
-        TBlockEvents<TEvDataShard::TEvSampleKResponse> sampleKBlocker(runtime, [&](const auto&) {
+        TBlockEvents<TEvDataShard::TEvLocalKMeansResponse> localKBlocker(runtime, [&](const auto&) {
             return true;
         });
-        runtime.WaitFor("sampleK", [&]{ return sampleKBlocker.size(); });
-        sampleKBlocker.Stop().Unblock();
+        runtime.WaitFor("localK", [&]{ return localKBlocker.size(); });
         {
             auto buildIndexOperations = TestListBuildIndex(runtime, tenantSchemeShard, "/MyRoot/CommonDB");
             UNIT_ASSERT_VALUES_EQUAL(buildIndexOperations.EntriesSize(), 1);
@@ -406,6 +405,7 @@ Y_UNIT_TEST_SUITE (VectorIndexBuildTest) {
                 NLs::PathExist,
                 NLs::IndexState(NKikimrSchemeOp::EIndexState::EIndexStateWriteOnly)});
         }
+        localKBlocker.Stop().Unblock();
 
         // Wait Done state:
         env.TestWaitNotification(runtime, buildIndexTx, tenantSchemeShard);