github-actions[bot] commented on code in PR #66849:
URL: https://github.com/apache/doris/pull/66849#discussion_r3796864543
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be/src/exec/scan/olap_scanner.cpp:
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@@ -496,16 +497,26 @@ Status OlapScanner::_init_tablet_reader_params(
add_return_column_if_absent(static_cast<uint32_t>(op_idx));
}
- for (auto cid : _return_columns) {
- if (cid >= tablet_schema->num_key_columns()) {
- const auto& col_name = tablet_schema->column(cid).name();
- std::string before_col_name;
- before_col_name.append("__BEFORE__");
- before_col_name.append(col_name);
- before_col_name.append("__");
- if (int32_t before_idx =
tablet_schema->field_index(before_col_name);
- before_idx >= 0) {
-
add_return_column_if_absent(static_cast<uint32_t>(before_idx));
+ if (is_min_delta_scan) {
+ // No-op UPDATE detection compares the complete row state at the
two ends of the
+ // window. Read every AFTER/BEFORE value column even when SQL
projects only a subset;
+ // BlockReader's return-column mapping keeps these comparison-only
columns hidden.
+ for (uint32_t cid = tablet_schema->num_key_columns();
+ cid < tablet_schema->num_columns(); ++cid) {
+ add_return_column_if_absent(cid);
Review Comment:
[P1] Build this full projection without a linear search per column.
add_return_column_if_absent() runs std::find over the growing return_columns
vector, and this new loop calls it for all C physical binlog columns, so each
tablet/range scanner now does roughly C^2/2 integer comparisons even for a
narrow query. That is separate from the quadratic name lookup later in
BlockReader. Please track selected dense column ids with a bitmap/set or append
the remaining schema columns in one linear pass while preserving the required
output order.
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