Function BTR_selectivity

src/jrd/btr.cpp:2387–2589

void BTR_selectivity(thread_db* tdbb, jrd_rel* relation, USHORT id, SelectivityList& selectivity)
{
/**************************************
 *
 *	B T R _ s e l e c t i v i t y
 *
 **************************************
 *
 * Functional description
 *	Update index selectivity on the fly.
 *	Note that index leaf pages are walked
 *	without visiting data pages. Thus the
 *	effects of uncommitted transactions
 *	will be included in the calculation.
 *
 **************************************/

	SET_TDBB(tdbb);
	RelationPages* relPages = relation->getPages(tdbb);
	WIN window(relPages->rel_pg_space_id, -1);

	index_root_page* root = fetch_root(tdbb, &window, relation, relPages);
	if (!root)
		return;

	ULONG page;
	if (id >= root->irt_count || !(page = root->irt_rpt[id].getRoot()))
	{
		CCH_RELEASE(tdbb, &window);
		return;
	}

	const bool descending = (root->irt_rpt[id].irt_flags & irt_descending);
	const ULONG segments = root->irt_rpt[id].irt_keys;

	window.win_flags = WIN_large_scan;
	window.win_scans = 1;
	btree_page* bucket = (btree_page*) CCH_HANDOFF(tdbb, &window, page, LCK_read, pag_index);

	// go down the left side of the index to leaf level
	UCHAR* pointer = bucket->btr_nodes + bucket->btr_jump_size;
	while (bucket->btr_level)
	{
		IndexNode pageNode;
		pageNode.readNode(pointer, false);
		bucket = (btree_page*) CCH_HANDOFF(tdbb, &window, pageNode.pageNumber, LCK_read, pag_index);
		pointer = bucket->btr_nodes + bucket->btr_jump_size;
		page = pageNode.pageNumber;
	}

	FB_UINT64 nodes = 0;
	FB_UINT64 duplicates = 0;
	temporary_key key;
	key.key_flags = 0;
	key.key_length = 0;
	SSHORT l;
	bool firstNode = true;