SERVER-58276 Add collscan plan if collection is clustered and collscan uses clustered index

5 files changed, 66 insertions, 29 deletions

diff --git a/jstests/core/cover_null_queries.js b/jstests/core/cover_null_queries.js
index c17b9e71929..7054a16039d 100644
--- a/jstests/core/cover_null_queries.js
+++ b/jstests/core/cover_null_queries.js
@@ -11,6 +11,7 @@
 
 load("jstests/aggregation/extras/utils.js");  // For arrayEq().
 load("jstests/libs/analyze_plan.js");         // For getAggPlanStages() and getPlanStages().
+load("jstests/libs/clustered_collections/clustered_collection_util.js");
 
 const coll = db.cover_null_queries;
 coll.drop();
@@ -95,6 +96,15 @@ function validateCountAggCmdOutputAndPlan({filter, expectedStages, expectedCount
     validateStages({cmdObj, expectedStages, isAgg: true});
 }
 
+function getExpectedStagesIndexScanAndFetch(extraStages) {
+    const clustered = ClusteredCollectionUtil.areAllCollectionsClustered(db.getMongo());
+    const result = clustered ? {"CLUSTERED_IXSCAN": 1} : {"FETCH": 1, "IXSCAN": 1};
+    for (const stage in extraStages) {
+        result[stage] = extraStages[stage];
+    }
+    return result;
+}
+
 assert.commandWorked(coll.createIndex({a: 1, _id: 1}));
 
 // Verify count({a: null}) can be covered by an index. In the simplest case we can use two count
@@ -272,18 +282,18 @@ validateFindCmdOutputAndPlan({
 validateSimpleCountCmdOutputAndPlan({
     filter: {a: null, _id: 3},
     expectedCount: 1,
-    expectedStages: {"FETCH": 1, "IXSCAN": 1, "OR": 0, "COUNT_SCAN": 0}
+    expectedStages: getExpectedStagesIndexScanAndFetch({"OR": 0, "COUNT_SCAN": 0}),
 });
 validateCountAggCmdOutputAndPlan({
     filter: {a: null, _id: 3},
     expectedCount: 1,
-    expectedStages: {"FETCH": 1, "IXSCAN": 1, "OR": 0, "COUNT_SCAN": 0},
+    expectedStages: getExpectedStagesIndexScanAndFetch({"OR": 0, "COUNT_SCAN": 0}),
 });
 validateFindCmdOutputAndPlan({
     filter: {a: null, _id: 3},
     projection: {_id: 1},
     expectedOutput: [{_id: 3}],
-    expectedStages: {"IXSCAN": 1, "FETCH": 1, "PROJECTION_SIMPLE": 1},
+    expectedStages: getExpectedStagesIndexScanAndFetch({"PROJECTION_SIMPLE": 1}),
 });
 
 // Verify that if the index is multikey and the query searches for null and empty array values, then
diff --git a/jstests/core/profile_update.js b/jstests/core/profile_update.js
index deeeb8ee8a3..ebd0505e58d 100644
--- a/jstests/core/profile_update.js
+++ b/jstests/core/profile_update.js
@@ -100,12 +100,9 @@ assert.commandWorked(coll.update({_id: "new value", a: 4}, {$inc: {b: 1}}, {upse
 profileObj = getLatestProfilerEntry(testDB);
 
 const collectionIsClustered = ClusteredCollectionUtil.areAllCollectionsClustered(db.getMongo());
-// A clustered collection has no actual index on _id. While a bounded collection scan is in
-// principle an efficient option, the query planner only defaults to collection scan if no suitable
-// index is available.
-const expectedPlan = collectionIsClustered ? "IXSCAN { a: 1 }" : "IXSCAN { _id: 1 }";
-const expectedKeysExamined = collectionIsClustered ? 1 : 0;
-const expectedDocsExamined = expectedKeysExamined;
+const expectedPlan = collectionIsClustered ? "CLUSTERED_IXSCAN" : "IXSCAN { _id: 1 }";
+const expectedKeysExamined = 0;
+const expectedDocsExamined = collectionIsClustered ? 1 : 0;
 const expectedKeysInserted = collectionIsClustered ? 1 : 2;
 
 assert.eq(profileObj.command,
@@ -149,13 +146,17 @@ for (var i = 0; i < indices.length; i++) {
     const profileObj = profiles[i];
     const index = indices[i];
 
-    // A clustered collection has no actual index on _id. While a bounded collection scan is in
-    // principle an efficient option, the query planner only defaults to collection scan if no
-    // suitable index is available.
-    const expectedPlan = collectionIsClustered ? "IXSCAN { a: 1 }" : "IXSCAN { _id: 1 }";
-    const expectedKeysExamined = collectionIsClustered ? 1 : 0;
-    const expectedDocsExamined = expectedKeysExamined;
-    const expectedKeysInserted = collectionIsClustered ? 1 : 2;
+    let expectedPlan = "IXSCAN { _id: 1 }";
+    let expectedKeysExamined = 0;
+    let expectedDocsExamined = 0;
+    let expectedKeysInserted = 2;
+
+    if (collectionIsClustered) {
+        expectedPlan = "CLUSTERED_IXSCAN";
+        expectedKeysExamined = 0;
+        expectedDocsExamined = (i + 1 == indices.length) ? 1 : 2;
+        expectedKeysInserted = 1;
+    }
 
     assert.eq(
         profileObj.command,
diff --git a/jstests/core/timeseries/timeseries_index_partial.js b/jstests/core/timeseries/timeseries_index_partial.js
index 55ece446457..7d97209173e 100644
--- a/jstests/core/timeseries/timeseries_index_partial.js
+++ b/jstests/core/timeseries/timeseries_index_partial.js
@@ -97,10 +97,24 @@ assert.commandFailedWithCode(coll.createIndex({a: 1}, {partialFilterExpression:
 
 // Test creating and using a partial index.
 {
-    // Make sure the query uses the {a: 1} index.
+    let ixscanInWinningPlan = 0;
+
+    // Make sure the {a: 1} index was considered for this query.
     function checkPlan(predicate) {
         const explain = coll.find(predicate).explain();
-        const scan = getAggPlanStage(explain, 'IXSCAN');
+        let scan = getAggPlanStage(explain, 'IXSCAN');
+        // If scan is not present, check rejected plans
+        if (scan === null) {
+            const rejectedPlans = getRejectedPlans(getAggPlanStage(explain, "$cursor")["$cursor"]);
+            if (rejectedPlans.length === 1) {
+                const scans = getPlanStages(getRejectedPlan(rejectedPlans[0]), "IXSCAN");
+                if (scans.length === 1) {
+                    scan = scans[0];
+                }
+            }
+        } else {
+            ixscanInWinningPlan++;
+        }
         const indexes = buckets.getIndexes();
         assert(scan,
                "Expected an index scan for predicate: " + tojson(predicate) +
@@ -109,7 +123,7 @@ assert.commandFailedWithCode(coll.createIndex({a: 1}, {partialFilterExpression:
     }
     // Make sure the query results match a collection-scan plan.
     function checkResults(predicate) {
-        const result = coll.aggregate({$match: predicate}).toArray();
+        const result = coll.aggregate([{$match: predicate}], {hint: {a: 1}}).toArray();
         const unindexed =
             coll.aggregate([{$_internalInhibitOptimization: {}}, {$match: predicate}]).toArray();
         assert.docEq(result, unindexed);
@@ -152,10 +166,6 @@ assert.commandFailedWithCode(coll.createIndex({a: 1}, {partialFilterExpression:
         const t1 = ISODate('2000-01-01T00:00:01Z');
         const t2 = ISODate('2000-01-01T00:00:02Z');
 
-        // When the collection is sharded, there is an index on time that can win, instead of the
-        // partial index. So only check the results in that case, not the plan.
-        const check = FixtureHelpers.isSharded(buckets) ? checkResults : checkPlanAndResults;
-
         assert.commandWorked(coll.dropIndex({a: 1}));
         assert.commandWorked(
             coll.createIndex({a: 1}, {partialFilterExpression: {[timeField]: {$lt: t1}}}));
@@ -184,6 +194,7 @@ assert.commandFailedWithCode(coll.createIndex({a: 1}, {partialFilterExpression:
     assert.commandWorked(coll.dropIndex({a: 1}));
     assert.sameMembers(coll.getIndexes(), extraIndexes);
     assert.sameMembers(buckets.getIndexes(), extraBucketIndexes);
+    assert.gt(ixscanInWinningPlan, 0);
 }
 
 // Check that partialFilterExpression can use a mixture of metadata, time, and measurement fields,
diff --git a/jstests/core/timeseries/timeseries_index_use.js b/jstests/core/timeseries/timeseries_index_use.js
index b1106e4ead0..ebcea9d8e6b 100644
--- a/jstests/core/timeseries/timeseries_index_use.js
+++ b/jstests/core/timeseries/timeseries_index_use.js
@@ -58,8 +58,9 @@ const generateTest = (useHint) => {
 
         /**
          * Creates the index specified by the spec and options, then explains the query to ensure
-         * that the created index is used. Runs the query and verifies that the expected number of
-         * documents are matched. Finally, deletes the created index.
+         * that the created index is used or was considered by multi-planner.
+         * Runs the query and verifies that the expected number of documents are matched.
+         * Finally, deletes the created index.
          */
         const testQueryUsesIndex = function(
             filter, numMatches, indexSpec, indexOpts = {}, queryOpts = {}) {
@@ -75,9 +76,23 @@ const generateTest = (useHint) => {
             assert.eq(numMatches, query.itcount());
 
             const explain = query.explain();
-            const ixscan = getAggPlanStage(explain, "IXSCAN");
-            assert.neq(null, ixscan, tojson(explain));
-            assert.eq("testIndexName", ixscan.indexName, tojson(ixscan));
+            if (useHint) {
+                const ixscan = getAggPlanStage(explain, "IXSCAN");
+                assert.neq(null, ixscan, tojson(explain));
+                assert.eq("testIndexName", ixscan.indexName, tojson(ixscan));
+            } else {
+                let ixscan = getAggPlanStage(explain, "IXSCAN");
+                // If ixscan is not present, check rejected plans
+                if (ixscan === null) {
+                    const rejectedPlans =
+                        getRejectedPlans(getAggPlanStage(explain, "$cursor")["$cursor"]);
+                    assert.eq(1, rejectedPlans.length);
+                    const ixscans = getPlanStages(getRejectedPlan(rejectedPlans[0]), "IXSCAN");
+                    assert.eq(1, ixscans.length);
+                    ixscan = ixscans[0];
+                }
+                assert.eq("testIndexName", ixscan.indexName, tojson(ixscan));
+            }
             assert.commandWorked(coll.dropIndex("testIndexName"));
         };
 
diff --git a/jstests/sharding/timeseries_query.js b/jstests/sharding/timeseries_query.js
index 4cf3b1c28c5..7a8b835c876 100644
--- a/jstests/sharding/timeseries_query.js
+++ b/jstests/sharding/timeseries_query.js
@@ -122,7 +122,7 @@ function runQuery(
                 if (expectCollScan) {
                     assert(isCollscan(sDB, winningPlan));
                 } else {
-                    assert(isIxscan(sDB, winningPlan));
+                    assert(isIxscan(sDB, winningPlan) || isClusteredIxscan(sDB, winningPlan));
                 }
             });
         });