From e3a5d0f90621f6571892defe4ba6ffafcc68f8ce Mon Sep 17 00:00:00 2001
From: Rui Liu <rui.liu@mongodb.com>
Date: Wed, 16 Mar 2022 18:43:11 +0000
Subject: SERVER-64551 Add feature flag to temporarily disable index join in
 all feature variants

---
 buildscripts/resmokeconfig/fully_disabled_feature_flags.yml |  2 ++
 jstests/noPassthrough/lookup_pushdown.js                    | 11 +++++++++--
 jstests/noPassthrough/lookup_pushdown_semantics.js          |  4 +++-
 src/mongo/db/query/planner_analysis.cpp                     |  6 +++++-
 src/mongo/db/query/query_feature_flags.idl                  |  5 +++++
 5 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/buildscripts/resmokeconfig/fully_disabled_feature_flags.yml b/buildscripts/resmokeconfig/fully_disabled_feature_flags.yml
index 036bf0029fd..f0a8a0b180c 100644
--- a/buildscripts/resmokeconfig/fully_disabled_feature_flags.yml
+++ b/buildscripts/resmokeconfig/fully_disabled_feature_flags.yml
@@ -11,4 +11,6 @@
 # Disable featureFlagSBELookupPushdown until integration tests can pass with basic SBE
 # lookup translation.
 - featureFlagSBELookupPushdown
+# TODO(SERVER-63574): Remove this feature flag and enable index join in all feature flag variant once all types of local fields are supported.
+- featureFlagSBELookupPushdownIndexJoin
 - featureFlagAutoParameterization
diff --git a/jstests/noPassthrough/lookup_pushdown.js b/jstests/noPassthrough/lookup_pushdown.js
index 6b7a6d64198..fee90c772fc 100644
--- a/jstests/noPassthrough/lookup_pushdown.js
+++ b/jstests/noPassthrough/lookup_pushdown.js
@@ -19,7 +19,9 @@ const JoinAlgorithm = {
 };
 
 // Standalone cases.
-const conn = MongoRunner.runMongod({setParameter: "featureFlagSBELookupPushdown=true"});
+const conn = MongoRunner.runMongod({
+    setParameter: {featureFlagSBELookupPushdown: true, featureFlagSBELookupPushdownIndexJoin: true}
+});
 assert.neq(null, conn, "mongod was unable to start up");
 const name = "lookup_pushdown";
 const foreignCollName = "foreign_lookup_pushdown";
@@ -636,7 +638,12 @@ MongoRunner.stopMongod(conn);
 const st = new ShardingTest({
     shards: 2,
     mongos: 1,
-    other: {shardOptions: {setParameter: "featureFlagSBELookupPushdown=true"}}
+    other: {
+        shardOptions: {
+            setParameter:
+                {featureFlagSBELookupPushdown: true, featureFlagSBELookupPushdownIndexJoin: true}
+        }
+    }
 });
 db = st.s.getDB(name);
 
diff --git a/jstests/noPassthrough/lookup_pushdown_semantics.js b/jstests/noPassthrough/lookup_pushdown_semantics.js
index f03da9f76c0..ba6d4204a8b 100644
--- a/jstests/noPassthrough/lookup_pushdown_semantics.js
+++ b/jstests/noPassthrough/lookup_pushdown_semantics.js
@@ -8,7 +8,9 @@ load("jstests/libs/sbe_util.js");  // For 'checkSBEEnabled()'.
 load("jstests/aggregation/extras/utils.js");
 
 // Standalone cases.
-const conn = MongoRunner.runMongod({setParameter: "featureFlagSBELookupPushdown=true"});
+const conn = MongoRunner.runMongod({
+    setParameter: {featureFlagSBELookupPushdown: true, featureFlagSBELookupPushdownIndexJoin: true}
+});
 assert.neq(null, conn, "mongod was unable to start up");
 const db = conn.getDB("lookup_pushdown");
 if (!checkSBEEnabled(db, ["featureFlagSBELookupPushdown"])) {
diff --git a/src/mongo/db/query/planner_analysis.cpp b/src/mongo/db/query/planner_analysis.cpp
index eacb67b69c3..cc570708a09 100644
--- a/src/mongo/db/query/planner_analysis.cpp
+++ b/src/mongo/db/query/planner_analysis.cpp
@@ -625,6 +625,10 @@ bool isEligibleForHashJoin(const SecondaryCollectionInfo& foreignCollInfo) {
         internalQueryCollectionMaxStorageSizeBytesToChooseHashJoin.load();
 }
 
+bool isEligibleForIndexedLoopJoin() {
+    return feature_flags::gFeatureFlagSBELookupPushdownIndexJoin.isEnabledAndIgnoreFCV();
+}
+
 // static
 void QueryPlannerAnalysis::determineLookupStrategy(
     EqLookupNode* eqLookupNode,
@@ -667,7 +671,7 @@ void QueryPlannerAnalysis::determineLookupStrategy(
         return boost::none;
     }();
 
-    if (foreignIndex) {
+    if (foreignIndex && isEligibleForIndexedLoopJoin()) {
         eqLookupNode->lookupStrategy = EqLookupNode::LookupStrategy::kIndexedLoopJoin;
         eqLookupNode->idxEntry = foreignIndex;
     } else if (allowDiskUse && isEligibleForHashJoin(foreignCollItr->second)) {
diff --git a/src/mongo/db/query/query_feature_flags.idl b/src/mongo/db/query/query_feature_flags.idl
index b60ea4d04cc..b213db5c907 100644
--- a/src/mongo/db/query/query_feature_flags.idl
+++ b/src/mongo/db/query/query_feature_flags.idl
@@ -137,6 +137,11 @@ feature_flags:
       cpp_varname: gFeatureFlagSBELookupPushdown
       default: false
 
+    featureFlagSBELookupPushdownIndexJoin:
+      description: "Feature flag for allowing SBE $lookup pushdown to execute query using index join strategy"
+      cpp_varname: gFeatureFlagSBELookupPushdownIndexJoin
+      default: false
+
     featureFlagSearchShardedFacets:
       description: "Enable use of $$SEARCH_META on sharded collections"
       cpp_varname: gFeatureFlagSearchShardedFacets
-- 
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