Merge 7af3488 into 77844b4

Author: ulya-sidorina

ydb/core/kqp/common/kqp_tx.cpp

@@ -184,6 +184,11 @@ bool NeedSnapshot(const TKqpTransactionContext& txCtx, const NYql::TKikimrConfig
         return true;
     }
 
+    // We always need snapshot for stream lookup, besause it's used for dependent reads
+    if (hasStreamLookup) {
+        return true;
+    }
+
     // We don't want snapshot when there are effects at the moment,
     // because it hurts performance when there are multiple single-shard
     // reads and a single distributed commit. Taking snapshot costs

ydb/core/kqp/executer_actor/kqp_tasks_graph.cpp

@@ -536,7 +536,8 @@ bool IsCrossShardChannel(const TKqpTasksGraph& tasksGraph, const TChannel& chann
         return false;
     }
 
-    return targetShard != tasksGraph.GetTask(channel.SrcTask).Meta.ShardId;
+    ui64 srcShard = tasksGraph.GetTask(channel.SrcTask).Meta.ShardId;
+    return srcShard && targetShard != srcShard;
 }
 
 void TShardKeyRanges::AddPoint(TSerializedCellVec&& point) {