C++ (Cpp) CBitSet::Equals Examples

Example #1

File: CJoinOrderDP.cpp Project: b-xiang/gporca

//---------------------------------------------------------------------------
//	@function:
//		CJoinOrderDP::PexprBestJoinOrder
//
//	@doc:
//		find best join order for a given set of elements;
//
//---------------------------------------------------------------------------
CExpression *
CJoinOrderDP::PexprBestJoinOrder
	(
	CBitSet *pbs
	)
{
	GPOS_CHECK_STACK_SIZE;
	GPOS_CHECK_ABORT;

	GPOS_ASSERT(NULL != pbs);

	// start by looking-up cost in the DP map
	CExpression *pexpr = PexprLookup(pbs);

	if (pexpr == m_pexprDummy)
	{
		// no join order could be created
		return NULL;
	}

	if (NULL != pexpr)
	{
		// join order is found by looking up map
		return pexpr;
	}

	// find maximal covered subset
	CBitSet *pbsCovered = PbsCovered(pbs);
	if (0 == pbsCovered->Size())
	{
		// set is not covered, return a cross product
		pbsCovered->Release();

		return PexprCross(pbs);
	}

	if (!pbsCovered->Equals(pbs))
	{
		// create a cross product for uncovered subset
		CBitSet *pbsUncovered = GPOS_NEW(m_mp) CBitSet(m_mp, *pbs);
		pbsUncovered->Difference(pbsCovered);
		CExpression *pexprResult =
			PexprJoinCoveredSubsetWithUncoveredSubset(pbs, pbsCovered, pbsUncovered);
		pbsCovered->Release();
		pbsUncovered->Release();

		return pexprResult;
	}
	pbsCovered->Release();

	// if set has size 2, there is only one possible solution
	if (2 == pbs->Size())
	{
		return PexprJoin(pbs);
	}

	// otherwise, compute best join order using dynamic programming
	CExpression *pexprBestJoinOrder = PexprBestJoinOrderDP(pbs);
	if (pexprBestJoinOrder == m_pexprDummy)
	{
		// no join order could be created
		return NULL;
	}

	return pexprBestJoinOrder;
}