greenplumn CLimitStatsProcessor 源码
greenplumn CLimitStatsProcessor 代码
文件路径：/src/backend/gporca/libnaucrates/src/statistics/CLimitStatsProcessor.cpp
//---------------------------------------------------------------------------
// Greenplum Database
// Copyright 2018 VMware, Inc. or its affiliates.
//
// @filename:
// CLimitStatsProcessor.cpp
//
// @doc:
// Statistics helper routines for processing limit operations
//---------------------------------------------------------------------------
#include "naucrates/statistics/CLimitStatsProcessor.h"
using namespace gpopt;
// compute the statistics of a limit operation
CStatistics *
CLimitStatsProcessor::CalcLimitStats(CMemoryPool *mp,
const CStatistics *input_stats,
CDouble input_limit_rows)
{
GPOS_ASSERT(nullptr != input_stats);
// copy the hash map from colid -> histogram for resultant structure
UlongToHistogramMap *colid_histogram = input_stats->CopyHistograms(mp);
CDouble limit_rows = CStatistics::MinRows;
if (!input_stats->IsEmpty())
{
limit_rows = std::max(CStatistics::MinRows, input_limit_rows);
}
// create an output stats object
CStatistics *pstatsLimit = GPOS_NEW(mp) CStatistics(
mp, colid_histogram, input_stats->CopyWidths(mp), limit_rows,
input_stats->IsEmpty(), input_stats->GetNumberOfPredicates());
// In the output statistics object, the upper bound source cardinality of the join column
// cannot be greater than the upper bound source cardinality information maintained in the input
// statistics object. Therefore we choose CStatistics::EcbmMin the bounding method which takes
// the minimum of the cardinality upper bound of the source column (in the input hash map)
// and estimated limit cardinality.
// modify source id to upper bound card information
CStatisticsUtils::ComputeCardUpperBounds(
mp, input_stats, pstatsLimit, limit_rows,
CStatistics::EcbmMin /* card_bounding_method */);
return pstatsLimit;
}
// EOF
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