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[improvement](scan) Align scanner split to segments for MATCH #67915

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[improvement](scan) Align scanner split to segments for MATCH #67915

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36 changes: 27 additions & 9 deletions be/src/exec/operator/olap_scan_operator.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -460,6 +460,17 @@ static bool contains_expr_node_type(const VExprSPtr& expr, TExprNodeType::type n
});
}

// Find MATCH recursively; ones nested in AND / OR / NOT count too.
static bool is_match_expr(const VExprSPtr& expr) {
DORIS_CHECK(expr != nullptr);
if (expr->node_type() == TExprNodeType::MATCH_PRED ||

@github-actions github-actions Bot Sep 14, 2026

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[P1] Gate this on index execution, not only on expression shape. With enable_inverted_index_query=false (or a MATCH column without an iterator), this still returns true even though SegmentIterator skips index evaluation and runs the supported row fallback. On a single large segment, the old row-count builder can split that expensive fallback across scanners, while this route creates exactly one scanner and serializes it; on many segments it also triggers the unbounded population noted separately. Row-only wrappers have the same false positive because their roots never dispatch evaluate_inverted_index() to the MATCH child. Require index execution to be enabled and a usable/index-evaluable root before selecting this strategy.

@csun5285 csun5285 Sep 14, 2026

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在cloud 上可以认为 match 的执行一定有倒排索引的

expr->node_type() == TExprNodeType::SEARCH_EXPR || expr->can_push_down_to_index()) {
return true;
}
return std::ranges::any_of(expr->children(),
[](const auto& child) { return is_match_expr(child); });
}

static Status validate_residual_scan_conjuncts(RuntimeState* state,
TPushAggOp::type push_down_agg_type,
const VExprContextSPtrs& conjuncts) {
Expand Down Expand Up @@ -635,6 +646,21 @@ bool OlapScanLocalState::_is_binlog_merge_scan() const {
return scan_type == TBinlogScanType::MIN_DELTA || scan_type == TBinlogScanType::DETAIL;
}

// Give each segment a scanner of its own for queries like:
// SELECT k1 FROM t ORDER BY l2_distance_approximate(embedding, [1.0, 2.0]) LIMIT 2
// SELECT k1 FROM t WHERE msg MATCH_PHRASE 'error timeout'
bool OlapScanLocalState::_use_scan_parallelism_by_per_segment() {
// TODO: Use optimize_index_scan_parallelism for ann range search in the future.
// Currently, ann topn is enough
if (state()->query_options().__isset.optimize_index_scan_parallelism &&
state()->query_options().optimize_index_scan_parallelism && _ann_topn_runtime != nullptr) {
return true;
}
return config::is_cloud_mode() &&

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[P1] Preserve global BM25 statistics before splitting by segment. This branch also covers score-enabled MATCH/SEARCH scans. Each generated scanner gets one segment from one rowset, and OlapScanner::_prepare_impl() builds a fresh CollectionStatistics from only that scanner's rs_splits; those rowset-local document-frequency and length values feed BM25. Rows from different rowsets are therefore ranked with incompatible IDF/avgdl values, so a final ORDER BY score() LIMIT ... can return the wrong row. Also, collection walks every segment of the supplied rowset, so an N-segment rowset now repeats that work N times. Compute/share statistics from the original complete read source, or keep score queries on the prior strategy, and add a cloud multi-rowset TopN regression.

@csun5285 csun5285 Sep 14, 2026

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CollectionStatistics 一直是按scanner 的粒度构建的

std::ranges::any_of(_common_expr_ctxs_push_down,

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[P2] Include pushed-down MATCH virtual-column projections in this decision. Projection-only MATCH is stored in _slot_id_to_virtual_column_expr, not _common_expr_ctxs_push_down, yet every scanner clones that context and SegmentIterator evaluates it over num_rows() for the whole segment before materializing the selected row range. A large segment split among N scanners therefore still repeats the same index evaluation N times, so this misses a supported path with the exact cost the PR targets. Inspect the virtual-column roots here as well (including any VirtualSlotRef unwrapping) and add a cloud projection regression.

@csun5285 csun5285 Sep 14, 2026 •
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不考虑 projection 先，仅针对 where 后面的倒排索引计算

[](const auto& ctx) { return is_match_expr(ctx->root()); });
}

Status OlapScanLocalState::_init_scanners(std::list<ScannerSPtr>* scanners) {
if (_scan_ranges.empty()) {
_eos = true;
Expand Down Expand Up @@ -764,15 +790,7 @@ Status OlapScanLocalState::_init_scanners(std::list<ScannerSPtr>* scanners) {
std::max<int64_t>(1024, state()->parallel_scan_min_rows_per_scanner());
scanner_builder.set_max_scanners_count(max_scanners_count);
scanner_builder.set_min_rows_per_scanner(min_rows_per_scanner);
// If the session variable is set, force one scanner per segment.
if (state()->query_options().__isset.optimize_index_scan_parallelism &&
state()->query_options().optimize_index_scan_parallelism) {
// TODO: Use optimize_index_scan_parallelism for ann range search in the future.
// Currently, ann topn is enough
if (_ann_topn_runtime != nullptr) {
scanner_builder.set_scan_parallelism_by_per_segment(true);
}
}
scanner_builder.set_scan_parallelism_by_per_segment(_use_scan_parallelism_by_per_segment());

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[P1] Keep segment-aligned scans within the configured scanner cap. _build_scanners_by_per_segment() creates one scanner for every segment and never consults parallel_scan_max_scanners_count or the minimum-rows setting; initialization then creates a delegate and pending task for every scanner before execution concurrency is applied. A cloud table with many historical segments can therefore allocate an unbounded scanner/task population even with the cap set to 1, and LIMIT/cancellation only clean it up afterward. Group whole segments into at most the configured number of scanner read sources so no segment is split while scanner cardinality remains bounded.

@csun5285 csun5285 Sep 14, 2026

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scanner 变多的代价很低


RETURN_IF_ERROR(scanner_builder.build_scanners(*scanners));
for (auto& scanner : *scanners) {
Expand Down
3 changes: 3 additions & 0 deletions be/src/exec/operator/olap_scan_operator.h
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Original file line number Diff line number Diff line change
Expand Up @@ -135,6 +135,9 @@ class OlapScanLocalState final : public ScanLocalState<OlapScanLocalState> {

Status _init_scanners(std::list<ScannerSPtr>* scanners) override;

// Whether each segment should be scanned by a scanner of its own.
bool _use_scan_parallelism_by_per_segment();

Status _build_key_ranges_and_filters();

bool _is_tablet_pruned_by_runtime_filter(int64_t partition_id, int32_t bucket_seq,
Expand Down
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