Function delete_tree

src/jrd/btr.cpp:3678–3742

static void delete_tree(thread_db* tdbb,
						USHORT rel_id, USHORT idx_id, PageNumber next, PageNumber prior)
{
/**************************************
 *
 *	d e l e t e _ t r e e
 *
 **************************************
 *
 * Functional description
 *	Release index pages back to free list.
 *
 **************************************/

	SET_TDBB(tdbb);
	WIN window(next.getPageSpaceID(), -1);
	window.win_flags = WIN_large_scan;
	window.win_scans = 1;

	ULONG down = next.getPageNum();
	// Delete the index tree from the top down.
	while (next.getPageNum())
	{
		window.win_page = next;
		btree_page* page = (btree_page*) CCH_FETCH(tdbb, &window, LCK_write, 0);

		// do a little defensive programming--if any of these conditions
		// are true we have a damaged pointer, so just stop deleting. At
		// the same time, allow updates of indexes with id > 255 even though
		// the page header uses a byte for its index id.  This requires relaxing
		// the check slightly introducing a risk that we'll pick up a page belonging
		// to some other index that is ours +/- (256*n).  On the whole, unlikely.
		if (page->btr_header.pag_type != pag_index ||
			page->btr_id != (UCHAR)(idx_id % 256) || page->btr_relation != rel_id)
		{
			CCH_RELEASE(tdbb, &window);
			return;
		}

		// if we are at the beginning of a non-leaf level, position
		// "down" to the beginning of the next level down
		if (next.getPageNum() == down)
		{
			if (page->btr_level)
			{
				UCHAR* pointer = page->btr_nodes + page->btr_jump_size;
				IndexNode pageNode;
				pageNode.readNode(pointer, false);
				down = pageNode.pageNumber;
			}
			else
				down = 0;
		}

		// go through all the sibling pages on this level and release them
		next = page->btr_sibling;
		CCH_RELEASE_TAIL(tdbb, &window);
		PAG_release_page(tdbb, window.win_page, prior);