From 588fdcffdf4f1883063db4f896d6a536291c072b Mon Sep 17 00:00:00 2001
From: vdimir <vdimir@clickhouse.com>
Date: Wed, 29 Mar 2023 09:42:32 +0000
Subject: [PATCH] comment child_plans in ReadFromMerge

---
 src/Storages/StorageMerge.cpp | 2 ++
 src/Storages/StorageMerge.h   | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/src/Storages/StorageMerge.cpp b/src/Storages/StorageMerge.cpp
index 40ad4ab0f26..00ccfebff25 100644
--- a/src/Storages/StorageMerge.cpp
+++ b/src/Storages/StorageMerge.cpp
@@ -655,6 +655,8 @@ QueryPipelineBuilderPtr ReadFromMerge::createSources(
         if (real_column_names.empty())
             real_column_names.push_back(ExpressionActions::getSmallestColumn(storage_snapshot->metadata->getColumns().getAllPhysical()).name);
 
+        /// Steps for reading from child tables should have the same lifetime as the current step
+        /// because `builder` can have references to them (mainly for EXPLAIN PIPELINE).
         QueryPlan & plan = child_plans.emplace_back();
 
         StorageView * view = dynamic_cast<StorageView *>(storage.get());
diff --git a/src/Storages/StorageMerge.h b/src/Storages/StorageMerge.h
index 602da045dfb..d53dcd34f5f 100644
--- a/src/Storages/StorageMerge.h
+++ b/src/Storages/StorageMerge.h
@@ -159,6 +159,8 @@ private:
     StoragePtr storage_merge;
     StorageSnapshotPtr merge_storage_snapshot;
 
+    /// Store read plan for each child table.
+    /// It's needed to guarantee lifetime for child steps to be the same as for this step.
     std::vector<QueryPlan> child_plans;
 
     SelectQueryInfo query_info;