From 173d5d0b98e6bcdf1b97ddf31152a5a6b76b3841 Mon Sep 17 00:00:00 2001
From: Antonio Andelic <antonio@clickhouse.com>
Date: Wed, 8 May 2024 12:15:54 +0200
Subject: [PATCH] Keep parent part alive for read task

---
 .../MergeTree/MergeTreePrefetchedReadPool.cpp  |  2 +-
 .../MergeTree/MergeTreeReadPoolBase.cpp        | 18 ++++++++++++++++++
 src/Storages/MergeTree/MergeTreeReadTask.h     |  2 ++
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/src/Storages/MergeTree/MergeTreePrefetchedReadPool.cpp b/src/Storages/MergeTree/MergeTreePrefetchedReadPool.cpp
index ebd19093f68..91cbdc79624 100644
--- a/src/Storages/MergeTree/MergeTreePrefetchedReadPool.cpp
+++ b/src/Storages/MergeTree/MergeTreePrefetchedReadPool.cpp
@@ -53,7 +53,7 @@ MergeTreePrefetchedReadPool::PrefetchedReaders::PrefetchedReaders(
     MergeTreePrefetchedReadPool & read_prefetch)
     : is_valid(true)
     , readers(std::move(readers_))
-    , prefetch_runner(pool, "Prefetch")
+    , prefetch_runner(pool, "ReadPrepare")
 {
     prefetch_runner(read_prefetch.createPrefetchedTask(readers.main.get(), priority_));
 
diff --git a/src/Storages/MergeTree/MergeTreeReadPoolBase.cpp b/src/Storages/MergeTree/MergeTreeReadPoolBase.cpp
index 0cbb0a86b2f..d4b9ce34796 100644
--- a/src/Storages/MergeTree/MergeTreeReadPoolBase.cpp
+++ b/src/Storages/MergeTree/MergeTreeReadPoolBase.cpp
@@ -6,6 +6,11 @@
 namespace DB
 {
 
+namespace ErrorCodes
+{
+    extern const int LOGICAL_ERROR;
+}
+
 MergeTreeReadPoolBase::MergeTreeReadPoolBase(
     RangesInDataParts && parts_,
     VirtualFields shared_virtual_fields_,
@@ -48,6 +53,19 @@ void MergeTreeReadPoolBase::fillPerPartInfos()
         MergeTreeReadTaskInfo read_task_info;
 
         read_task_info.data_part = part_with_ranges.data_part;
+
+        const auto & data_part = read_task_info.data_part;
+        if (data_part->isProjectionPart())
+        {
+            read_task_info.parent_part = data_part->storage.getPartIfExists(
+                data_part->getParentPartName(),
+                {MergeTreeDataPartState::PreActive, MergeTreeDataPartState::Active, MergeTreeDataPartState::Outdated});
+
+            if (!read_task_info.parent_part)
+                throw Exception(ErrorCodes::LOGICAL_ERROR, "Did not find parent part {} for projection part {}",
+                            data_part->getParentPartName(), data_part->getDataPartStorage().getFullPath());
+        }
+
         read_task_info.part_index_in_query = part_with_ranges.part_index_in_query;
         read_task_info.alter_conversions = part_with_ranges.alter_conversions;
 
diff --git a/src/Storages/MergeTree/MergeTreeReadTask.h b/src/Storages/MergeTree/MergeTreeReadTask.h
index c8bb501c0e8..3af95b9cdce 100644
--- a/src/Storages/MergeTree/MergeTreeReadTask.h
+++ b/src/Storages/MergeTree/MergeTreeReadTask.h
@@ -56,6 +56,8 @@ struct MergeTreeReadTaskInfo
 {
     /// Data part which should be read while performing this task
     DataPartPtr data_part;
+    /// Parent part of the projection part
+    DataPartPtr parent_part;
     /// For `part_index` virtual column
     size_t part_index_in_query;
     /// Alter converversionss that should be applied on-fly for part.