//--------------------------------------------------------------------------- // @function: // CCostContext::ComputeCost // // @doc: // Compute cost of current context, // // the function extracts cardinality and row width of owner operator // and child operators, and then adjusts row estimate obtained from // statistics based on data distribution obtained from plan properties, // // statistics row estimate is computed on logical expressions by // estimating the size of the whole relation regardless data // distribution, on the other hand, optimizer's cost model computes // the cost of a plan instance on some segment, // // when a plan produces tuples distributed to multiple segments, we // need to divide statistics row estimate by the number segments to // provide a per-segment row estimate for cost computation, // // Note that this scaling of row estimate cannot happen during // statistics derivation since plans are not created yet at this point // // this function also extracts number of rebinds of owner operator child // operators, if statistics are computed using predicates with external // parameters (outer references), number of rebinds is the total number // of external parameters' values // //--------------------------------------------------------------------------- CCost CCostContext::CostCompute ( IMemoryPool *pmp, DrgPcost *pdrgpcostChildren ) { // derive context stats DeriveStats(); ULONG ulArity = 0; if (NULL != m_pdrgpoc) { ulArity = Pdrgpoc()->UlLength(); } m_pstats->AddRef(); ICostModel::SCostingInfo ci(pmp, ulArity, GPOS_NEW(pmp) ICostModel::CCostingStats(m_pstats)); ICostModel *pcm = COptCtxt::PoctxtFromTLS()->Pcm(); CExpressionHandle exprhdl(pmp); exprhdl.Attach(this); // extract local costing info DOUBLE dRows = m_pstats->DRows().DVal(); if (CDistributionSpec::EdptPartitioned == Pdpplan()->Pds()->Edpt()) { // scale statistics row estimate by number of segments dRows = DRowsPerHost().DVal(); } ci.SetRows(dRows); DOUBLE dWidth = m_pstats->DWidth(pmp, m_poc->Prpp()->PcrsRequired()).DVal(); ci.SetWidth(dWidth); DOUBLE dRebinds = m_pstats->DRebinds().DVal(); ci.SetRebinds(dRebinds); GPOS_ASSERT_IMP(!exprhdl.FHasOuterRefs(), GPOPT_DEFAULT_REBINDS == (ULONG) (dRebinds) && "invalid number of rebinds when there are no outer references"); // extract children costing info for (ULONG ul = 0; ul < ulArity; ul++) { COptimizationContext *pocChild = (*m_pdrgpoc)[ul]; CCostContext *pccChild = pocChild->PccBest(); GPOS_ASSERT(NULL != pccChild); IStatistics *pstatsChild = pccChild->Pstats(); DOUBLE dRowsChild = pstatsChild->DRows().DVal(); if (CDistributionSpec::EdptPartitioned == pccChild->Pdpplan()->Pds()->Edpt()) { // scale statistics row estimate by number of segments dRowsChild = pccChild->DRowsPerHost().DVal(); } ci.SetChildRows(ul, dRowsChild); DOUBLE dWidthChild = pstatsChild->DWidth(pmp, pocChild->Prpp()->PcrsRequired()).DVal(); ci.SetChildWidth(ul, dWidthChild); DOUBLE dRebindsChild = pstatsChild->DRebinds().DVal(); ci.SetChildRebinds(ul, dRebindsChild); GPOS_ASSERT_IMP(!exprhdl.FHasOuterRefs(ul), GPOPT_DEFAULT_REBINDS == (ULONG) (dRebindsChild) && "invalid number of rebinds when there are no outer references"); DOUBLE dCostChild = (*pdrgpcostChildren)[ul]->DVal(); ci.SetChildCost(ul, dCostChild); } // compute cost using the underlying cost model return pcm->Cost(exprhdl, &ci); }