Waloid24 commented on PR #2067:
URL: https://github.com/apache/cloudberry/pull/2067#issuecomment-5917388183
It literally does the same as
`CScaleFactorUtils::CalcScaleFactorCumulativeConj` here:
```
void
CScaleFactorUtils::SortScalingFactor(CDoubleArray *scale_factors,
BOOL
is_descending)
{
GPOS_ASSERT(nullptr != scale_factors);
const ULONG num_cols = scale_factors->Size();
if (1 < num_cols)
{
if (is_descending)
{
// sort (in desc order) the scaling factor based on the
selectivity of each column
scale_factors->Sort(CScaleFactorUtils::DescendingOrderCmpFunc);
}
else
{
// sort (in ascending order) the scaling factor based
on the selectivity of each column
scale_factors->Sort(CScaleFactorUtils::AscendingOrderCmpFunc);
}
}
}
```
We have descending order, so we will do the same action:
`scale_factors->Sort(CScaleFactorUtils::DescendingOrderCmpFunc);` as
`CScaleFactorUtils::CalcScaleFactorCumulativeConj` (see below) does:
- `if (1 < num_cols)` then we sort it in the descending order:
`scale_factors->Sort(CScaleFactorUtils::DescendingOrderCmpFunc);`
- otherwise doesn't sort at all
```
CDouble
CScaleFactorUtils::CalcScaleFactorCumulativeConj(
const CStatisticsConfig *stats_config, CDoubleArray *scale_factors)
{
GPOS_ASSERT(nullptr != stats_config);
GPOS_ASSERT(nullptr != scale_factors);
const ULONG num_cols = scale_factors->Size();
CDouble scale_factor(1.0);
if (1 < num_cols)
{
// sort (in desc order) the scaling factor based on the
selectivity of each column
scale_factors->Sort(CScaleFactorUtils::DescendingOrderCmpFunc);
}
for (ULONG ul = 0; ul < num_cols; ul++)
{
// apply damping factor
CDouble local_scale_factor = *(*scale_factors)[ul];
scale_factor =
scale_factor * std::max(CStatistics::MinRows.Get(),
(local_scale_factor *
CScaleFactorUtils::DampedFilterScaleFactor(
stats_config, ul + 1))
.Get());
}
return scale_factor;
}
```
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