Merge 'Don't do any I/O if top level operator is Nothing' from Jussi Saurio

Small tweak Before: ``` limbo> explain select * from users where 0; addr opcode p1 p2 p3 p4 p5 comment ---- ----------------- ---- ---- ---- ------------- -- ------- 0 Init 0 21 0 0 Start at 21 1 OpenReadAsync 0 2 0 0 table=users, root=2 2 OpenReadAwait 0 0 0 0 3 RewindAsync 0 0 0 0 4 RewindAwait 0 20 0 0 Rewind table users 5 Integer 0 1 0 0 r[1]=0 6 IfNot 1 18 1 0 if !r[1] goto 18 7 RowId 0 2 0 0 r[2]=users.rowid 8 Column 0 1 3 0 r[3]=users.first_name 9 Column 0 2 4 0 r[4]=users.last_name 10 Column 0 3 5 0 r[5]=users.email 11 Column 0 4 6 0 r[6]=users.phone_number 12 Column 0 5 7 0 r[7]=users.address 13 Column 0 6 8 0 r[8]=users.city 14 Column 0 7 9 0 r[9]=users.state 15 Column 0 8 10 0 r[10]=users.zipcode 16 Column 0 9 11 0 r[11]=users.age 17 ResultRow 2 10 0 0 output=r[2..11] 18 NextAsync 0 0 0 0 19 NextAwait 0 4 0 0 20 Halt 0 0 0 0 21 Transaction 0 0 0 0 22 Goto 0 1 0 0 ``` After: ``` limbo> explain select * from users where 0; addr opcode p1 p2 p3 p4 p5 comment ---- ----------------- ---- ---- ---- ------------- -- ------- 0 Init 0 2 0 0 Start at 2 1 Halt 0 0 0 0 2 Transaction 0 0 0 0 3 Goto 0 1 0 0 ``` Closes #306
2026-01-05 01:04:22 +01:00 · 2024-08-25 13:23:20 +03:00
parent 84ed081f19 d1059da9f1
commit 053ba5e126
2 changed files with 57 additions and 30 deletions
--- a/core/translate/optimizer.rs
+++ b/core/translate/optimizer.rs
@@ -16,7 +16,14 @@ pub fn optimize_plan(mut select_plan: Plan) -> Result<Plan> {
        &mut select_plan.root_operator,
        &select_plan.referenced_tables,
    )?;
-    eliminate_constants(&mut select_plan.root_operator)?;
+    if eliminate_constants(&mut select_plan.root_operator)?
+        == ConstantConditionEliminationResult::ImpossibleCondition
+    {
+        return Ok(Plan {
+            root_operator: Operator::Nothing,
+            referenced_tables: vec![],
+        });
+    }
    use_indexes(
        &mut select_plan.root_operator,
        &select_plan.referenced_tables,
@@ -116,9 +123,15 @@ fn use_indexes(
    }
 }

+#[derive(Debug, PartialEq, Clone)]
+enum ConstantConditionEliminationResult {
+    Continue,
+    ImpossibleCondition,
+}
+
 // removes predicates that are always true
-// returns false if there is an impossible predicate that is always false
-fn eliminate_constants(operator: &mut Operator) -> Result<bool> {
+// returns a ConstantEliminationResult indicating whether any predicates are always false
+fn eliminate_constants(operator: &mut Operator) -> Result<ConstantConditionEliminationResult> {
    match operator {
        Operator::Filter {
            source, predicates, ..
@@ -129,7 +142,7 @@ fn eliminate_constants(operator: &mut Operator) -> Result<bool> {
                if predicate.is_always_true()? {
                    predicates.remove(i);
                } else if predicate.is_always_false()? {
-                    return Ok(false);
+                    return Ok(ConstantConditionEliminationResult::ImpossibleCondition);
                } else {
                    i += 1;
                }
@@ -142,7 +155,7 @@ fn eliminate_constants(operator: &mut Operator) -> Result<bool> {
                eliminate_constants(source)?;
            }

-            return Ok(true);
+            return Ok(ConstantConditionEliminationResult::Continue);
        }
        Operator::Join {
            left,
@@ -151,15 +164,19 @@ fn eliminate_constants(operator: &mut Operator) -> Result<bool> {
            outer,
            ..
        } => {
-            if !eliminate_constants(left)? {
-                return Ok(false);
+            if eliminate_constants(left)? == ConstantConditionEliminationResult::ImpossibleCondition
+            {
+                return Ok(ConstantConditionEliminationResult::ImpossibleCondition);
            }
-            if !eliminate_constants(right)? && !*outer {
-                return Ok(false);
+            if eliminate_constants(right)?
+                == ConstantConditionEliminationResult::ImpossibleCondition
+                && !*outer
+            {
+                return Ok(ConstantConditionEliminationResult::ImpossibleCondition);
            }

            if predicates.is_none() {
-                return Ok(true);
+                return Ok(ConstantConditionEliminationResult::Continue);
            }

            let predicates = predicates.as_mut().unwrap();
@@ -170,20 +187,22 @@ fn eliminate_constants(operator: &mut Operator) -> Result<bool> {
                if predicate.is_always_true()? {
                    predicates.remove(i);
                } else if predicate.is_always_false()? && !*outer {
-                    return Ok(false);
+                    return Ok(ConstantConditionEliminationResult::ImpossibleCondition);
                } else {
                    i += 1;
                }
            }

-            return Ok(true);
+            return Ok(ConstantConditionEliminationResult::Continue);
        }
        Operator::Aggregate { source, .. } => {
-            let ok = eliminate_constants(source)?;
-            if !ok {
+            if eliminate_constants(source)?
+                == ConstantConditionEliminationResult::ImpossibleCondition
+            {
                *source = Box::new(Operator::Nothing);
            }
-            return Ok(ok);
+            // Aggregation operator can return a row even if the source is empty e.g. count(1) from users where 0
+            return Ok(ConstantConditionEliminationResult::Continue);
        }
        Operator::SeekRowid {
            rowid_predicate,
@@ -197,7 +216,7 @@ fn eliminate_constants(operator: &mut Operator) -> Result<bool> {
                    if predicate.is_always_true()? {
                        predicates.remove(i);
                    } else if predicate.is_always_false()? {
-                        return Ok(false);
+                        return Ok(ConstantConditionEliminationResult::ImpossibleCondition);
                    } else {
                        i += 1;
                    }
@@ -205,31 +224,38 @@ fn eliminate_constants(operator: &mut Operator) -> Result<bool> {
            }

            if rowid_predicate.is_always_false()? {
-                return Ok(false);
+                return Ok(ConstantConditionEliminationResult::ImpossibleCondition);
            }

-            return Ok(true);
+            return Ok(ConstantConditionEliminationResult::Continue);
        }
        Operator::Limit { source, .. } => {
-            let ok = eliminate_constants(source)?;
-            if !ok {
+            let constant_elimination_result = eliminate_constants(source)?;
+            if constant_elimination_result
+                == ConstantConditionEliminationResult::ImpossibleCondition
+            {
                *operator = Operator::Nothing;
            }
-            return Ok(ok);
+            return Ok(constant_elimination_result);
        }
        Operator::Order { source, .. } => {
-            let ok = eliminate_constants(source)?;
-            if !ok {
+            if eliminate_constants(source)?
+                == ConstantConditionEliminationResult::ImpossibleCondition
+            {
                *operator = Operator::Nothing;
+                return Ok(ConstantConditionEliminationResult::ImpossibleCondition);
            }
-            return Ok(true);
+            return Ok(ConstantConditionEliminationResult::Continue);
        }
        Operator::Projection { source, .. } => {
-            let ok = eliminate_constants(source)?;
-            if !ok {
+            if eliminate_constants(source)?
+                == ConstantConditionEliminationResult::ImpossibleCondition
+            {
                *operator = Operator::Nothing;
+                return Ok(ConstantConditionEliminationResult::ImpossibleCondition);
            }
-            return Ok(ok);
+
+            return Ok(ConstantConditionEliminationResult::Continue);
        }
        Operator::Scan { predicates, .. } => {
            if let Some(ps) = predicates {
@@ -239,7 +265,7 @@ fn eliminate_constants(operator: &mut Operator) -> Result<bool> {
                    if predicate.is_always_true()? {
                        ps.remove(i);
                    } else if predicate.is_always_false()? {
-                        return Ok(false);
+                        return Ok(ConstantConditionEliminationResult::ImpossibleCondition);
                    } else {
                        i += 1;
                    }
@@ -249,9 +275,9 @@ fn eliminate_constants(operator: &mut Operator) -> Result<bool> {
                    *predicates = None;
                }
            }
-            return Ok(true);
+            return Ok(ConstantConditionEliminationResult::Continue);
        }
-        Operator::Nothing => return Ok(true),
+        Operator::Nothing => return Ok(ConstantConditionEliminationResult::Continue),
    }
 }

--- a/core/translate/plan.rs
+++ b/core/translate/plan.rs
@@ -8,6 +8,7 @@ use sqlite3_parser::ast;

 use crate::{function::AggFunc, schema::BTreeTable, util::normalize_ident, Result};

+#[derive(Debug)]
 pub struct Plan {
    pub root_operator: Operator,
    pub referenced_tables: Vec<(Rc<BTreeTable>, String)>,