From 4c5a7cda088457d7b823a82d22d87d52d7eabf48 Mon Sep 17 00:00:00 2001
From: Pekka Enberg <penberg@iki.fi>
Date: Thu, 2 Oct 2025 12:24:53 +0300
Subject: [PATCH] core/vdbe: Avoid cloning Arc<MvStore> on every VDBE step

The VDBE step() function was taking Arc<MvStore> by value, causing it to
be cloned on every single step of query execution. This resulted in
thousands of atomic reference count increments/decrements per query,
showing up as a major hotspot in profiling.

Changed step() and related functions to take Option<&Arc<MvStore>>
instead, passing a reference rather than cloning the Arc. This eliminates
the unnecessary atomic operations while maintaining the same semantics.
---
 core/lib.rs      |  6 +++---
 core/vdbe/mod.rs | 14 +++++++-------
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/core/lib.rs b/core/lib.rs
index 034c01d08..55370df4c 100644
--- a/core/lib.rs
+++ b/core/lib.rs
@@ -2472,7 +2472,7 @@ impl Statement {
         let mut res = if !self.accesses_db {
             self.program.step(
                 &mut self.state,
-                self.mv_store.clone(),
+                self.mv_store.as_ref(),
                 self.pager.clone(),
                 self.query_mode,
             )
@@ -2480,7 +2480,7 @@ impl Statement {
             const MAX_SCHEMA_RETRY: usize = 50;
             let mut res = self.program.step(
                 &mut self.state,
-                self.mv_store.clone(),
+                self.mv_store.as_ref(),
                 self.pager.clone(),
                 self.query_mode,
             );
@@ -2493,7 +2493,7 @@ impl Statement {
                 self.reprepare()?;
                 res = self.program.step(
                     &mut self.state,
-                    self.mv_store.clone(),
+                    self.mv_store.as_ref(),
                     self.pager.clone(),
                     self.query_mode,
                 );
diff --git a/core/vdbe/mod.rs b/core/vdbe/mod.rs
index fa0521b2a..f688e09a3 100644
--- a/core/vdbe/mod.rs
+++ b/core/vdbe/mod.rs
@@ -512,7 +512,7 @@ impl Program {
     pub fn step(
         &self,
         state: &mut ProgramState,
-        mv_store: Option<Arc<MvStore>>,
+        mv_store: Option<&Arc<MvStore>>,
         pager: Arc<Pager>,
         query_mode: QueryMode,
     ) -> Result<StepResult> {
@@ -526,7 +526,7 @@ impl Program {
     fn explain_step(
         &self,
         state: &mut ProgramState,
-        _mv_store: Option<Arc<MvStore>>,
+        _mv_store: Option<&Arc<MvStore>>,
         pager: Arc<Pager>,
     ) -> Result<StepResult> {
         debug_assert!(state.column_count() == EXPLAIN_COLUMNS.len());
@@ -580,7 +580,7 @@ impl Program {
     fn explain_query_plan_step(
         &self,
         state: &mut ProgramState,
-        _mv_store: Option<Arc<MvStore>>,
+        _mv_store: Option<&Arc<MvStore>>,
         pager: Arc<Pager>,
     ) -> Result<StepResult> {
         debug_assert!(state.column_count() == EXPLAIN_QUERY_PLAN_COLUMNS.len());
@@ -628,7 +628,7 @@ impl Program {
     fn normal_step(
         &self,
         state: &mut ProgramState,
-        mv_store: Option<Arc<MvStore>>,
+        mv_store: Option<&Arc<MvStore>>,
         pager: Arc<Pager>,
     ) -> Result<StepResult> {
         let enable_tracing = tracing::enabled!(tracing::Level::TRACE);
@@ -650,7 +650,7 @@ impl Program {
                 }
                 if let Some(err) = io.get_error() {
                     let err = err.into();
-                    handle_program_error(&pager, &self.connection, &err, mv_store.as_ref())?;
+                    handle_program_error(&pager, &self.connection, &err, mv_store)?;
                     return Err(err);
                 }
                 state.io_completions = None;
@@ -665,7 +665,7 @@ impl Program {
             // Always increment VM steps for every loop iteration
             state.metrics.vm_steps = state.metrics.vm_steps.saturating_add(1);
 
-            match insn_function(self, state, insn, &pager, mv_store.as_ref()) {
+            match insn_function(self, state, insn, &pager, mv_store) {
                 Ok(InsnFunctionStepResult::Step) => {
                     // Instruction completed, moving to next
                     state.metrics.insn_executed = state.metrics.insn_executed.saturating_add(1);
@@ -694,7 +694,7 @@ impl Program {
                     return Ok(StepResult::Busy);
                 }
                 Err(err) => {
-                    handle_program_error(&pager, &self.connection, &err, mv_store.as_ref())?;
+                    handle_program_error(&pager, &self.connection, &err, mv_store)?;
                     return Err(err);
                 }
             }