fix splitter condition to avoid split micro-chunks (#10375)

Author: ivanmorozov333

ydb/core/tx/columnshard/splitter/batch_slice.cpp

@@ -99,6 +99,8 @@ bool TGeneralSerializedSlice::GroupBlobsImpl(const NSplitter::TGroupFeatures& fe
                         chunksInProgress.PopFront(i);
                         hasNoSplitChanges = true;
                     } else {
+                        // in this case chunksInProgress[i] size >= Max - Min for case nextPartSize >= features.GetSplitSettings().GetMaxBlobSize()
+                        // in this case chunksInProgress[i] size >= Max - 2 * Min for case nextOtherSize < features.GetSplitSettings().GetMinBlobSize()
                         Y_ABORT_UNLESS((i64)chunksInProgress[i]->GetPackedSize() > features.GetSplitSettings().GetMinBlobSize() - partSize);
                         Y_ABORT_UNLESS(otherSize - (features.GetSplitSettings().GetMinBlobSize() - partSize) >= features.GetSplitSettings().GetMinBlobSize());
 

ydb/core/tx/columnshard/splitter/settings.h

@@ -14,8 +14,10 @@ namespace NKikimr::NOlap::NSplitter {
 
 class TSplitSettings {
 private:
+// DefaultMaxBlobSize - 2 * DefaultMinBlobSize have to been enought to "guarantee" records count > 1 through blobs splitting
     static const inline i64 DefaultMaxBlobSize = 8 * 1024 * 1024;
-    static const inline i64 DefaultMinBlobSize = 4 * 1024 * 1024;
+    static const inline i64 DefaultMinBlobSize = 3 * 1024 * 1024;
+
     static const inline i64 DefaultMinRecordsCount = 10000;
     static const inline i64 DefaultMaxPortionSize = 6 * DefaultMaxBlobSize;
     YDB_ACCESSOR(i64, MaxBlobSize, DefaultMaxBlobSize);