github-actions[bot] commented on code in PR #66849:
URL: https://github.com/apache/doris/pull/66849#discussion_r3796864537
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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();
Review Comment:
[P1] Preflight unsupported types before widening the projection. If any
value is BITMAP, HLL, QUANTILE_STATE, or another rejected shape, BlockReader
permanently sets comparison completeness to false, so this optimization can
never suppress a group. This loop nevertheless reads every unrequested AFTER
and BEFORE value on every block; even a key-only MIN_DELTA query on a BITMAP
table now pays the large extra I/O for no behavior change. When complete
comparison is statically impossible, preserve the old narrow projection (and
keep the runtime check conservative).
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