[GitHub] [doris] xiaokang commented on a diff in pull request #15558: [Improvement](topn) runtime prune for topn query

[GitBox <gi...@apache.org>]

xiaokang commented on code in PR #15558:
URL: https://github.com/apache/doris/pull/15558#discussion_r1060690642


##########
be/src/vec/exec/vsort_node.cpp:
##########
@@ -123,6 +126,33 @@ Status VSortNode::open(RuntimeState* state) {
                                   _children[0], std::placeholders::_1, std::placeholders::_2,
                                   std::placeholders::_3)),
                 child(0)->get_next_span(), eos);
+
+        if (upstream_block->rows() != 0) {
+            RETURN_IF_ERROR(_sorter->append_block(upstream_block.get()));
+            RETURN_IF_CANCELLED(state);
+            RETURN_IF_ERROR(state->check_query_state("vsort, while sorting input."));
+
+            // runtime predicate
+            // SCOPED_TIMER(_update_runtime_predicate_timer);
+            if (_use_topn_opt) {
+                Field new_top = _sorter->get_top_value();
+                if (!new_top.is_null() && new_top != old_top) {
+                    auto & sort_description = _sorter->get_sort_description();
+                    auto col = upstream_block->get_by_position(sort_description[0].column_number);
+                    auto type = remove_nullable(col.type)->get_type_id();
+                    bool is_reverse = sort_description[0].direction < 0;
+                    auto query_ctx = _runtime_state->get_query_fragments_ctx();
+                    std::vector<vectorized::Field> values = {new_top};

Review Comment:
   Using vector is for further processing for multiple sort columns in query like `ORDER BY a, b LIMIT n`. But now only values[0] is used.
   
   After more consideration, I think only the first column can be used for push down even for multiple sort columns. So I will change the vector to a single value.



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