branch-4.0: [improvement](storage) Release unused memory earlier, rather than leaving it to the memory pool for guaranteed release #57215

be/src/olap/memtable.cpp

@@ -481,7 +481,7 @@ void MemTable::_clear_row_agg(RowInBlock* row) {
         row->remove_init_agg();
     }
 }
-
+// only in `to_block` the `is_final` flag will be true, in other cases, it will be false
 template <bool is_final, bool has_skip_bitmap_col>
 void MemTable::_aggregate() {
     SCOPED_RAW_TIMER(&_stat.agg_ns);
@@ -506,10 +506,15 @@ void MemTable::_aggregate() {
                 }
                 _stat.merged_rows++;
                 _aggregate_two_row_in_block<has_skip_bitmap_col>(mutable_block, cur_row, prev_row);
+                // Clean up aggregation state of the merged row to avoid memory leak
+                if (cur_row) {
+                    _clear_row_agg(cur_row);
+                }
             } else {
                 prev_row = cur_row;
                 if (!temp_row_in_blocks.empty()) {
-                    // no more rows to merge for prev row, finalize it
+                    // The rows from the previous batch of _row_in_blocks have been merged into temp_row_in_blocks,
+                    // now call finalize to write the aggregation results into _output_mutable_block.
                     _finalize_one_row<is_final>(temp_row_in_blocks.back().get(), block_data,
                                                 row_pos);
                 }