Backport ClickHouse#84158 to 25.6: Fix crash during lighweight mutation with projections

Author: robot-clickhouse

src/Storages/MergeTree/MutateTask.cpp

@@ -1277,6 +1277,10 @@ bool PartMergerWriter::mutateOriginalPartAndPrepareProjections()
                 ProfileEventTimeIncrement<Microseconds> projection_watch(ProfileEvents::MutateTaskProjectionsCalculationMicroseconds);
                 Block block_to_squash = ctx->projections_to_build[i]->calculate(cur_block, ctx->context);
 
+                /// Everything is deleted by lighweight delete
+                if (block_to_squash.rows() == 0)
+                    continue;
+
                 projection_squashes[i].setHeader(block_to_squash.cloneEmpty());
                 squashed_chunk = Squashing::squash(projection_squashes[i].add({block_to_squash.getColumns(), block_to_squash.rows()}));
             }

src/Storages/ProjectionsDescription.cpp

@@ -167,6 +167,9 @@ class ProjectionDataSink : public ISink
 
     String getName() const override { return "ProjectionDataSink"; }
 
+    /// Accumulated data can be empty if DELETE query deleted all the rows from block
+    bool isAccumulatedSomething() const { return accumulated_chunk && accumulated_chunk.getNumRows() > 0; }
+
     Columns detachAccumulatedColumns() { return accumulated_chunk.detachColumns(); }
 
 protected:
@@ -499,19 +502,22 @@ Block ProjectionDescription::calculate(const Block & block, ContextPtr context,
     pipeline.complete(sink);
     CompletedPipelineExecutor executor(pipeline);
     executor.execute();
-    auto projection_block = sink->getPort().getHeader().cloneWithColumns(sink->detachAccumulatedColumns());
-    chassert(projection_block.rows() > 0);
-
-    /// Rename parent _part_offset to _parent_part_offset column
-    if (with_parent_part_offset)
+    Block projection_block;
+    if (sink->isAccumulatedSomething())
     {
-        chassert(projection_block.has("_part_offset"));
-        chassert(!projection_block.has("_parent_part_offset"));
-
-        auto new_column = projection_block.getByName("_part_offset");
-        new_column.name = "_parent_part_offset";
-        projection_block.erase("_part_offset");
-        projection_block.insert(std::move(new_column));
+      projection_block = sink->getPort().getHeader().cloneWithColumns(sink->detachAccumulatedColumns());
+
+      /// Rename parent _part_offset to _parent_part_offset column
+      if (with_parent_part_offset)
+      {
+          chassert(projection_block.has("_part_offset"));
+          chassert(!projection_block.has("_parent_part_offset"));
+
+          auto new_column = projection_block.getByName("_part_offset");
+          new_column.name = "_parent_part_offset";
+          projection_block.erase("_part_offset");
+          projection_block.insert(std::move(new_column));
+      }
     }
 
     return projection_block;

tests/queries/0_stateless/03571_lwd_and_projections.reference

@@ -0,0 +1,26 @@
+DROP TABLE IF EXISTS weird_projections;
+
+CREATE TABLE weird_projections(
+    `account_id` UInt64,
+    `user_id` String,
+    PROJECTION events_by_day_proj
+    (
+        SELECT
+            account_id,
+            countDistinct(user_id) AS total_users
+        GROUP BY
+            account_id
+    )
+)
+ENGINE = ReplicatedMergeTree('/clickhouse/{database}/tables/test', '1')
+ORDER BY (account_id)
+SETTINGS index_granularity = 8192, lightweight_mutation_projection_mode = 'rebuild';
+
+INSERT INTO weird_projections SELECT 134 as account_id, toString(account_id) as user_id FROM numbers(10000);
+INSERT INTO weird_projections SELECT 132 as account_id, toString(account_id) as user_id FROM numbers(10000);
+
+OPTIMIZE TABLE weird_projections FINAL;
+
+DELETE FROM weird_projections WHERE account_id = 134;
+
+DROP TABLE IF EXISTS weird_projections;