SERVER-63283 Add query knob to guard HJ plans for $lookup

3 files changed, 29 insertions, 0 deletions

diff --git a/jstests/noPassthrough/lookup_pushdown.js b/jstests/noPassthrough/lookup_pushdown.js
index 22a7806f5d2..0c13dadc16d 100644
--- a/jstests/noPassthrough/lookup_pushdown.js
+++ b/jstests/noPassthrough/lookup_pushdown.js
@@ -378,6 +378,30 @@ MongoRunner.stopMongod(conn);
             JoinAlgorithm.HJ,
             {allowDiskUse: true});
 
+    // Setting the 'internalQueryDisableLookupExecutionUsingHashJoin' knob to true will disable
+    // HJ plans from being chosen and since the pipeline is SBE compatible it will fallback to
+    // NLJ.
+    assert.commandWorked(db.adminCommand({
+        setParameter: 1,
+        internalQueryDisableLookupExecutionUsingHashJoin: true,
+    }));
+
+    runTest(lcoll,
+            [{$lookup: {from: fcoll.getName(), localField: "a", foreignField: "a", as: "out"}}],
+            JoinAlgorithm.NLJ,
+            {allowDiskUse: true});
+
+    // Test that we can go back to generating HJ plans.
+    assert.commandWorked(db.adminCommand({
+        setParameter: 1,
+        internalQueryDisableLookupExecutionUsingHashJoin: false,
+    }));
+
+    runTest(lcoll,
+            [{$lookup: {from: fcoll.getName(), localField: "a", foreignField: "a", as: "out"}}],
+            JoinAlgorithm.HJ,
+            {allowDiskUse: true});
+
     // Setting the 'internalQueryCollectionMaxNoOfDocumentsToChooseHashJoin' to count - 1 results in
     // choosing the NLJ algorithm.
     assert.commandWorked(db.adminCommand({
diff --git a/jstests/noPassthrough/query_knobs_validation.js b/jstests/noPassthrough/query_knobs_validation.js
index 671a95d7b84..36db1f286f2 100644
--- a/jstests/noPassthrough/query_knobs_validation.js
+++ b/jstests/noPassthrough/query_knobs_validation.js
@@ -53,6 +53,7 @@ const expectedParamDefaults = {
     internalQueryCollectionMaxNoOfDocumentsToChooseHashJoin: 10 * 1000,
     internalQueryCollectionMaxDataSizeBytesToChooseHashJoin: 100 * 1024 * 1024,
     internalQueryCollectionMaxStorageSizeBytesToChooseHashJoin: 100 * 1024 * 1024,
+    internalQueryDisableLookupExecutionUsingHashJoin: false,
 };
 
 function assertDefaultParameterValues() {
@@ -224,5 +225,8 @@ assertSetParameterSucceeds("internalQueryCollectionMaxStorageSizeBytesToChooseHa
 assertSetParameterFails("internalQueryCollectionMaxStorageSizeBytesToChooseHashJoin", 0);
 assertSetParameterFails("internalQueryCollectionMaxStorageSizeBytesToChooseHashJoin", -1);
 
+assertSetParameterSucceeds("internalQueryDisableLookupExecutionUsingHashJoin", true);
+assertSetParameterSucceeds("internalQueryDisableLookupExecutionUsingHashJoin", false);
+
 MongoRunner.stopMongod(conn);
 })();
diff --git a/jstests/noPassthrough/sbe_plan_cache_clear_on_param_change.js b/jstests/noPassthrough/sbe_plan_cache_clear_on_param_change.js
index e1b3e39b417..8a9cc66e4e7 100644
--- a/jstests/noPassthrough/sbe_plan_cache_clear_on_param_change.js
+++ b/jstests/noPassthrough/sbe_plan_cache_clear_on_param_change.js
@@ -34,6 +34,7 @@ const paramList = [
     {name: "internalQueryCollectionMaxNoOfDocumentsToChooseHashJoin", value: 1},
     {name: "internalQueryCollectionMaxDataSizeBytesToChooseHashJoin", value: 100},
     {name: "internalQueryCollectionMaxStorageSizeBytesToChooseHashJoin", value: 100},
+    {name: "internalQueryDisableLookupExecutionUsingHashJoin", value: true},
 ];
 
 const conn = MongoRunner.runMongod();