review fixes

Author: ztlpn

ydb/core/statistics/aggregator/analyze_actor.cpp

@@ -24,14 +24,16 @@ class TCMSEval : public IColumnStatisticEval {
     static std::optional<TCMSEval> MaybeCreate(
             const NKikimrStat::TSimpleColumnStatistics& simpleStats,
             const NScheme::TTypeInfo&) {
-        if (simpleStats.GetCountDistinct() >= 0.8 * simpleStats.GetCount()) {
+        if (simpleStats.GetCount() == 0 || simpleStats.GetCountDistinct() == 0) {
+            // Empty table
             return std::nullopt;
         }
 
         const double n = simpleStats.GetCount();
         const double ndv = simpleStats.GetCountDistinct();
-        if (ndv == 0) {
-            return TCMSEval(MIN_WIDTH);
+
+        if (ndv >= 0.8 * n) {
+            return std::nullopt;
         }
 
         const double c = 10;
@@ -208,7 +210,7 @@ void TAnalyzeActor::Handle(TEvTxProxySchemeCache::TEvNavigateKeySetResult::TPtr&
         for (const auto& colTag : RequestedColumnTags) {
             auto colIt = tag2Column.find(colTag);
             if (colIt == tag2Column.end()) {
-                // Column probably already deleted, skip it.
+                // Column probably already dropped, skip it.
                 continue;
             }
             addColumn(colIt->second);
@@ -219,6 +221,14 @@ void TAnalyzeActor::Handle(TEvTxProxySchemeCache::TEvNavigateKeySetResult::TPtr&
         }
     }
 
+    if (Columns.empty()) {
+        // All requested columns were already dropped. Send empty response right away.
+        auto response = std::make_unique<TEvStatistics::TEvFinishTraversal>(std::move(Results));
+        Send(Parent, response.release());
+        PassAway();
+        return;
+    }
+
     Become(&TThis::StateQueryStage1);
     auto actor = std::make_unique<TScanActor>(
         SelfId(), DatabaseName, stage1Builder.Build(TableName), stage1Builder.ColumnCount());
@@ -263,7 +273,6 @@ void TAnalyzeActor::HandleStage1(TEvPrivate::TEvAnalyzeScanResult::TPtr& ev) {
                 continue;
             }
             if (statEval->EstimateSize() >= 4_MB) {
-                // To avoid: Error: ydb/library/yql/dq/runtime/dq_output_channel.cpp:405: Row data size is too big: 53839241 bytes, exceeds limit of 50331648 bytes
                 continue;
             }
             statEval->AddAggregations(col.Name, stage2Builder);

ydb/core/statistics/aggregator/analyze_actor.h

@@ -55,7 +55,7 @@ class TAnalyzeActor : public NActors::TActorBootstrapped<TAnalyzeActor> {
             , Name(std::move(name))
         {}
         TColumnDesc(TColumnDesc&&) noexcept = default;
-        TColumnDesc& operator=(TColumnDesc&) noexcept = default;
+        TColumnDesc& operator=(TColumnDesc&&) noexcept = default;
 
         NKikimrStat::TSimpleColumnStatistics ExtractSimpleStats(
             ui64 count, const TVector<NYdb::TValue>& aggColumns) const;

ydb/core/statistics/service/ut/ut_column_statistics.cpp

@@ -34,7 +34,7 @@ Y_UNIT_TEST_SUITE(ColumnStatistics) {
 
         std::vector<TCountMinSketchProbes> expected = {
             {
-                .Tag = 2, // Key column
+                .Tag = 2, // Value column
                 .Probes{ {"1", 100}, {"2", 100} }
             }
         };