Allow position cardinality < 1, it's valid when multiple conjuncts are used (and it provides better cost estimations)

Author: dyemanov

src/jrd/optimizer/InnerJoin.cpp

@@ -189,15 +189,14 @@ void InnerJoin::estimateCost(unsigned position,
 	// Remember selectivity of this stream
 	joinedStreams[position].selectivity = candidate->selectivity;
 
+	// Calculate the nested loop cost, it's our default option
+	const auto loopCost = candidate->cost * cardinality;
+	cost = loopCost;
+
 	// Get the stream cardinality
 	const auto streamCardinality = csb->csb_rpt[stream->number].csb_cardinality;
 
-	// If the table looks like empty during preparation time, we cannot be sure about
-	// its real cardinality during execution. So, unless we have some index-based
-	// filtering applied, let's better be pessimistic and avoid hash joining due to
-	// likely cardinality under-estimation.
-	const bool avoidHashJoin = (streamCardinality <= MINIMUM_CARDINALITY && !stream->baseIndexes);
-
+	// Calculate the retrieval cardinality
 	auto currentCardinality = streamCardinality * candidate->selectivity;
 
 	// Given the "first-rows" mode specified (or implied)
@@ -212,9 +211,11 @@ void InnerJoin::estimateCost(unsigned position,
 	if ((candidate->unique || firstRows) && currentCardinality > MINIMUM_CARDINALITY)
 		currentCardinality = MINIMUM_CARDINALITY;
 
-	// Calculate the nested loop cost, it's our default option
-	const auto loopCost = candidate->cost * cardinality;
-	cost = loopCost;
+	// If the table looks like empty during preparation time, we cannot be sure about
+	// its real cardinality during execution. So, unless we have some index-based
+	// filtering applied, let's better be pessimistic and avoid hash joining due to
+	// likely cardinality under-estimation.
+	const bool avoidHashJoin = (streamCardinality <= MINIMUM_CARDINALITY && !stream->baseIndexes);
 
 	// Consider whether the current stream can be hash-joined to the prior ones.
 	// Beware conditional retrievals, this is impossible for them.
@@ -271,7 +272,7 @@ void InnerJoin::estimateCost(unsigned position,
 		}
 	}
 
-	cardinality = MAX(currentCardinality, MINIMUM_CARDINALITY);
+	cardinality = currentCardinality;
 }
 
 

src/jrd/optimizer/Optimizer.h

@@ -434,15 +434,9 @@ class Optimizer final : public Firebird::PermanentStorage
 		return MIN(selectivity, MAXIMUM_SELECTIVITY / 2);
 	}
 
-	static void adjustSelectivity(double& selectivity, double factor, double cardinality) noexcept
+	static void adjustSelectivity(double& selectivity, double factor) noexcept
 	{
-		if (!cardinality)
-			cardinality = DEFAULT_CARDINALITY;
-
-		const auto minSelectivity = MAXIMUM_SELECTIVITY / cardinality;
-		const auto diffSelectivity = selectivity > minSelectivity ?
-			selectivity - minSelectivity : 0;
-		selectivity = minSelectivity + diffSelectivity * factor;
+		selectivity = MIN(selectivity * factor, MAXIMUM_SELECTIVITY);
 	}
 
 	bool deliverJoinConjuncts(const BoolExprNodeStack& conjuncts) const

src/jrd/optimizer/Retrieval.cpp

@@ -355,7 +355,7 @@ InversionCandidate* Retrieval::getInversion()
 		}
 	}
 
-	Optimizer::adjustSelectivity(invCandidate->selectivity, selectivity, cardinality);
+	Optimizer::adjustSelectivity(invCandidate->selectivity, selectivity);
 
 	// Add the streams where this stream is depending on
 	for (auto match : invCandidate->matches)
@@ -419,7 +419,7 @@ IndexTableScan* Retrieval::getNavigation(const InversionCandidate* candidate)
 			}
 		}
 
-		Optimizer::adjustSelectivity(selectivity, factor, streamCardinality);
+		Optimizer::adjustSelectivity(selectivity, factor);
 
 		// Don't consider external sorting if optimization for first rows is requested
 		// and we have no local filtering applied

src/jrd/recsrc/FilteredStream.cpp

@@ -46,14 +46,7 @@ FilteredStream::FilteredStream(CompilerScratch* csb, RecordSource* next,
 	fb_assert(m_next && m_boolean);
 
 	m_impure = csb->allocImpure<Impure>();
-
-	auto cardinality = next->getCardinality();
-	if (selectivity)
-	{
-		Optimizer::adjustSelectivity(selectivity, MAXIMUM_SELECTIVITY, cardinality);
-		cardinality *= selectivity;
-	}
-	m_cardinality = cardinality;
+	m_cardinality = next->getCardinality() * selectivity;
 }
 
 FilteredStream::FilteredStream(CompilerScratch* csb, RecordSource* next,