Function reduce_scan_op

src/execution_plan/optimizations/utilize_indices.c:291–420

try to replace given Label Scan operation and a set of Filter operations with a single Index Scan operation

// try to replace given Label Scan operation and a set of Filter operations with
// a single Index Scan operation
void reduce_scan_op
(
	ExecutionPlan *plan,
	NodeByLabelScan *scan
) {
	// in the multi-label case, we want to pick the label which will allow us to
	// both utilize an index and iterate over the fewest values
	GraphContext *gc  =  QueryCtx_GetGraphCtx();
	Graph        *g   =  QueryCtx_GetGraph();
	QueryGraph   *qg  =  scan->op.plan->query_graph;

	// find label with filtered indexed properties
	// that has the minimum NNZ entries
	int         min_label_id;                 // tracks min label ID
	uint64_t    min_nnz        = UINT64_MAX;  // tracks min entries
	RSIndex     *rs_idx        = NULL;        // the index to be applied
	OpFilter    **filters      = NULL;        // tracks indexed filters to apply
	uint        filters_count  = 0;           // number of matching filters
	const char  *min_label_str = NULL;        // tracks min label name

	// see if scanned node has multiple labels
	const char *node_alias = scan->n->alias;
	QGNode *qn = QueryGraph_GetNodeByAlias(qg, node_alias);
	ASSERT(qn != NULL);

	uint label_count = QGNode_LabelCount(qn);
	for(uint i = 0; i < label_count; i++) {
		Index idx;
		uint64_t nnz;
		int label_id = QGNode_GetLabelID(qn, i);
		const char *label = QGNode_GetLabel(qn, i);

		// unknown label
		if(label_id == GRAPH_UNKNOWN_LABEL) continue;

		idx = GraphContext_GetIndexByID(gc, label_id, NULL, 0, IDX_EXACT_MATCH,
				GETYPE_NODE);

		// no index for current label
		if(idx == NULL) continue;

		ASSERT(Index_Enabled(idx));

		// TODO switch to reusable array
		OpFilter **cur_filters = _applicableFilters((OpBase *)scan, scan->n->alias, idx);

		// TODO consider heuristic which combines max
		// number / restrictiveness of applicable filters
		// vs. the label's NNZ?
		uint cur_filters_count = array_len(cur_filters);
		if(cur_filters_count == 0) {
			// no filters
			array_free(cur_filters);
			continue;
		}

		// get all applicable filter for index
		RSIndex *cur_idx = Index_RSIndex(idx);