Method findBestOrder

src/jrd/optimizer/InnerJoin.cpp:355–491

//

void InnerJoin::findBestOrder(unsigned position,
							  StreamInfo* stream,
							  IndexedRelationships& processList,
							  double cost,
							  double cardinality)
{
	const auto tail = &csb->csb_rpt[stream->number];

	// Do some initializations
	tail->activate();
	joinedStreams[position].reset(stream->number);

	// Save the various flag bits from the optimizer block to reset its
	// state after each test
	HalfStaticArray<bool, OPT_STATIC_ITEMS> streamFlags(innerStreams.getCount());
	for (const auto innerStream : innerStreams)
		streamFlags.add(innerStream->used);

	// Compute delta and total estimate cost to fetch this stream
	double positionCost = 0, positionCardinality = cardinality, newCost = 0, newCardinality = 0;

	if (!plan)
	{
		estimateCost(position, stream, positionCost, positionCardinality);
		newCost = cost + positionCost;
		newCardinality = cardinality * positionCardinality;
	}

	position++;

	// If the partial order is either longer than any previous partial order,
	// or the same length and cheap, save order as "best"
	if (position > bestCount || (position == bestCount && newCost < bestCost))
	{
		bestCount = position;
		bestCost = newCost;
		bestStreams.assign(joinedStreams.begin(), position);
	}

#ifdef OPT_DEBUG
	// Debug information
	printFoundOrder(position, positionCost, positionCardinality, newCost, newCardinality);
#endif

	// Mark this stream as "used" in the sense that it is already included
	// in this particular proposed stream ordering
	stream->used = true;
	bool done = false;

	// If we've used up all the streams there's no reason to go any further
	if (position == remainingStreams)
		done = true;

	// If we know a combination with all streams used and the
	// current cost is higher as the one from the best we're done
	if (bestCount == remainingStreams && bestCost < newCost)
		done = true;