chore: add some annotations for bugfix

Author: xudong963

src/query/service/src/pipelines/pipeline_builder.rs

@@ -829,7 +829,6 @@ impl PipelineBuilder {
             || join.join_type == JoinType::Single)
             && join.non_equi_conditions.is_empty()
         {
-            // self.main_pipeline.resize(1)?;
             self.main_pipeline.add_transform(|input, output| {
                 let transform = TransformLeftJoin::try_create(
                     input,

src/query/service/src/pipelines/processors/transforms/transform_left_join.rs

@@ -53,6 +53,8 @@ impl Compactor for LeftJoinCompactor {
 
     // `compact_final` is called when all the blocks are pushed
     fn compact_final(&self, blocks: &[DataBlock]) -> Result<Vec<DataBlock>> {
+        // If upstream data block is small, all blocks will be in rest blocks
+        // So compact partial won't be triggered, we still need to compact final here.
         self.hash_join_state.left_join_blocks(blocks)
     }
 }