From 6d4bb36425e36c56946b99a3b1a35cd309044a3d Mon Sep 17 00:00:00 2001
From: Tpt <thomaspt@hotmail.fr>
Date: Wed, 13 Oct 2021 19:25:16 +0200
Subject: [PATCH] Uses Reduced everywhere cardinality is not important

Allows avoiding dumb downstream duplicated work and should hopefully unlock optimizations in the future.
---
 lib/src/sparql/mod.rs          |  8 ++++----
 lib/src/sparql/plan_builder.rs | 11 +++++++++++
 lib/src/sparql/update.rs       |  2 +-
 3 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/lib/src/sparql/mod.rs b/lib/src/sparql/mod.rs
index 0042421e..16c17f85 100644
--- a/lib/src/sparql/mod.rs
+++ b/lib/src/sparql/mod.rs
@@ -48,7 +48,7 @@ pub(crate) fn evaluate_query(
         spargebra::Query::Select {
             pattern, base_iri, ..
         } => {
-            let (plan, variables) = PlanBuilder::build(&dataset, &pattern)?;
+            let (plan, variables) = PlanBuilder::build(&dataset, &pattern, true)?;
             Ok(SimpleEvaluator::new(
                 Rc::new(dataset),
                 base_iri.map(Rc::new),
@@ -67,7 +67,7 @@ pub(crate) fn evaluate_query(
         spargebra::Query::Ask {
             pattern, base_iri, ..
         } => {
-            let (plan, _) = PlanBuilder::build(&dataset, &pattern)?;
+            let (plan, _) = PlanBuilder::build(&dataset, &pattern, false)?;
             SimpleEvaluator::new(
                 Rc::new(dataset),
                 base_iri.map(Rc::new),
@@ -81,7 +81,7 @@ pub(crate) fn evaluate_query(
             base_iri,
             ..
         } => {
-            let (plan, variables) = PlanBuilder::build(&dataset, &pattern)?;
+            let (plan, variables) = PlanBuilder::build(&dataset, &pattern, false)?;
             let construct = PlanBuilder::build_graph_template(&dataset, &template, variables);
             Ok(SimpleEvaluator::new(
                 Rc::new(dataset),
@@ -93,7 +93,7 @@ pub(crate) fn evaluate_query(
         spargebra::Query::Describe {
             pattern, base_iri, ..
         } => {
-            let (plan, _) = PlanBuilder::build(&dataset, &pattern)?;
+            let (plan, _) = PlanBuilder::build(&dataset, &pattern, false)?;
             Ok(SimpleEvaluator::new(
                 Rc::new(dataset),
                 base_iri.map(Rc::new),
diff --git a/lib/src/sparql/plan_builder.rs b/lib/src/sparql/plan_builder.rs
index d5b4da72..8afb8396 100644
--- a/lib/src/sparql/plan_builder.rs
+++ b/lib/src/sparql/plan_builder.rs
@@ -19,6 +19,7 @@ impl<'a> PlanBuilder<'a> {
     pub fn build(
         dataset: &'a DatasetView,
         pattern: &GraphPattern,
+        is_cardinality_meaningful: bool,
     ) -> Result<(PlanNode, Vec<Variable>), EvaluationError> {
         let mut variables = Vec::default();
         let plan = PlanBuilder { dataset }.build_for_graph_pattern(
@@ -26,6 +27,15 @@ impl<'a> PlanBuilder<'a> {
             &mut variables,
             &PatternValue::Constant(EncodedTerm::DefaultGraph),
         )?;
+        let plan = if is_cardinality_meaningful {
+            plan
+        } else {
+            // let's reduce downstream task.
+            // TODO: avoid if already REDUCED or DISTINCT
+            PlanNode::Reduced {
+                child: Box::new(plan),
+            }
+        };
         Ok((plan, variables))
     }
 
@@ -1253,6 +1263,7 @@ impl<'a> PlanBuilder<'a> {
                 expression,
                 position,
             } => {
+                //TODO: handle the case where the filter generates an expression variable
                 if filter_variables.iter().all(|v| child.is_variable_bound(*v)) {
                     PlanNode::Extend {
                         child: Box::new(Self::push_filter(child, filter)),
diff --git a/lib/src/sparql/update.rs b/lib/src/sparql/update.rs
index 744d9592..59628216 100644
--- a/lib/src/sparql/update.rs
+++ b/lib/src/sparql/update.rs
@@ -120,7 +120,7 @@ impl<'a> SimpleUpdateEvaluator<'a> {
         algebra: &GraphPattern,
     ) -> Result<(), EvaluationError> {
         let dataset = Rc::new(DatasetView::new(self.storage.clone(), using));
-        let (plan, variables) = PlanBuilder::build(dataset.as_ref(), algebra)?;
+        let (plan, variables) = PlanBuilder::build(dataset.as_ref(), algebra, false)?;
         let evaluator = SimpleEvaluator::new(
             dataset.clone(),
             self.base_iri.clone(),