From 6e894361a4d9949e619c270bf2bf4ba13892821f Mon Sep 17 00:00:00 2001
From: Joan Fontanals <jfontanalsmartinez@gmail.com>
Date: Wed, 25 Mar 2026 17:07:27 +0100
Subject: [PATCH] MOD-14618 Fix race condition when calling `indexLabelCount`
 on SVS without locks (#919)

* proposal to fix flaky test

* clarify scope

* fiox preferAdHocSearch and add comment to indexLabelCount()

* revert preferAdHocSearch

---------

Co-authored-by: meiravgri <meirav.grimberg@redis.com>
(cherry picked from commit 42fdc908140236aea0ca359904f202080b935848)
---
 src/VecSim/vec_sim_tiered_index.h | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/src/VecSim/vec_sim_tiered_index.h b/src/VecSim/vec_sim_tiered_index.h
index ae18b8571..1e7708765 100644
--- a/src/VecSim/vec_sim_tiered_index.h
+++ b/src/VecSim/vec_sim_tiered_index.h
@@ -420,14 +420,22 @@ VecSimDebugInfoIterator *VecSimTieredIndex<DataType, DistType>::debugInfoIterato
                          .fieldType = INFOFIELD_UINT64,
                          .fieldValue = {FieldValue{.uintegerValue = info.tieredInfo.bufferLimit}}});
 
-    infoIterator->addInfoField(VecSim_InfoField{
-        .fieldName = VecSimCommonStrings::FRONTEND_INDEX_STRING,
-        .fieldType = INFOFIELD_ITERATOR,
-        .fieldValue = {FieldValue{.iteratorValue = this->frontendIndex->debugInfoIterator()}}});
+    // Acquire shared locks to safely access each sub-index's debug info during background indexing.
+    // Only hold each lock while accessing its respective index to minimize contention.
+    {
+        std::shared_lock<std::shared_mutex> flat_lock(this->flatIndexGuard);
+        infoIterator->addInfoField(VecSim_InfoField{
+            .fieldName = VecSimCommonStrings::FRONTEND_INDEX_STRING,
+            .fieldType = INFOFIELD_ITERATOR,
+            .fieldValue = {FieldValue{.iteratorValue = this->frontendIndex->debugInfoIterator()}}});
+    }
 
-    infoIterator->addInfoField(VecSim_InfoField{
-        .fieldName = VecSimCommonStrings::BACKEND_INDEX_STRING,
-        .fieldType = INFOFIELD_ITERATOR,
-        .fieldValue = {FieldValue{.iteratorValue = this->backendIndex->debugInfoIterator()}}});
+    {
+        std::shared_lock<std::shared_mutex> main_lock(this->mainIndexGuard);
+        infoIterator->addInfoField(VecSim_InfoField{
+            .fieldName = VecSimCommonStrings::BACKEND_INDEX_STRING,
+            .fieldType = INFOFIELD_ITERATOR,
+            .fieldValue = {FieldValue{.iteratorValue = this->backendIndex->debugInfoIterator()}}});
+    }
     return infoIterator;
 };