SERVER-47640 $lookup should increment the serverStatus metrics.queryExecutor counters

1 files changed, 114 insertions, 0 deletions

diff --git a/jstests/aggregation/sources/lookup/lookup_query_stats.js b/jstests/aggregation/sources/lookup/lookup_query_stats.js
new file mode 100644
index 00000000000..9b5c3ca2099
--- /dev/null
+++ b/jstests/aggregation/sources/lookup/lookup_query_stats.js
@@ -0,0 +1,114 @@
+/**
+ * Tests that the queryExecutor stats are correctly returned when $lookup is performed on
+ * foreign collection.
+ *
+ * @tags: [assumes_unsharded_collection]
+ */
+(function() {
+"use strict";
+
+const testDB = db.getSiblingDB("lookup_query_stats");
+testDB.dropDatabase();
+
+const localColl = testDB.getCollection("local");
+const fromColl = testDB.getCollection("foreign");
+const foreignDocCount = 10;
+const localDocCount = 2;
+
+// Keeps track of the last query execution stats.
+let lastScannedObjects = 0;
+let lastScannedKeys = 0;
+
+let insertDocumentToCollection = function(collection, docCount, fieldName) {
+    const bulk = collection.initializeUnorderedBulkOp();
+    for (let i = 0; i < docCount; i++) {
+        let doc = {_id: i};
+        doc[fieldName] = i;
+        bulk.insert(doc);
+    }
+    assert.commandWorked(bulk.execute());
+};
+
+let doAggregationLookup = function(localColl, fromColl) {
+    return localColl.aggregate([
+        {
+            $lookup: {
+                from: fromColl.getName(),
+                localField: "localField",
+                foreignField: "foreignField",
+                as: "output"
+            }
+        },
+        {
+            $sort: {_id: 1}
+        }]).toArray();
+};
+
+let getCurentQueryExecutorStats = function() {
+    let queryExecutor = testDB.serverStatus().metrics.queryExecutor;
+
+    let curScannedObjects = queryExecutor.scannedObjects - lastScannedObjects;
+    let curScannedKeys = queryExecutor.scanned - lastScannedKeys;
+
+    lastScannedObjects = queryExecutor.scannedObjects;
+    lastScannedKeys = queryExecutor.scanned;
+
+    return [curScannedObjects, curScannedKeys];
+};
+
+let testQueryExecutorStatsWithCollectionScan = function() {
+    let output = doAggregationLookup(localColl, fromColl);
+
+    let expectedOutput = [
+        {_id: 0, localField: 0, output: [{_id: 0, foreignField: 0}]},
+        {_id: 1, localField: 1, output: [{_id: 1, foreignField: 1}]}
+    ];
+
+    assert.eq(output, expectedOutput);
+
+    let [curScannedObjects, curScannedKeys] = getCurentQueryExecutorStats();
+
+    // For collection scan, total scannedObjects should be sum of
+    // (total documents in local collection +
+    //  total documents in local collection * total documents in foreign collection)
+    assert.eq(localDocCount + localDocCount * foreignDocCount, curScannedObjects);
+
+    // There is no index in the collection.
+    assert.eq(0, curScannedKeys);
+};
+
+let createIndexForCollection = function(collection, fieldName) {
+    let request = {};
+    request[fieldName] = 1;
+    assert.commandWorked(collection.createIndex(request));
+};
+
+let testQueryExecutorStatsWithIndexScan = function() {
+    createIndexForCollection(fromColl, "foreignField");
+
+    let output = doAggregationLookup(localColl, fromColl);
+
+    let expectedOutput = [
+        {_id: 0, localField: 0, output: [{_id: 0, foreignField: 0}]},
+        {_id: 1, localField: 1, output: [{_id: 1, foreignField: 1}]}
+    ];
+
+    assert.eq(output, expectedOutput);
+
+    let [curScannedObjects, curScannedKeys] = getCurentQueryExecutorStats();
+
+    // For index scan, total scannedObjects should be sum of
+    // (total documents in local collection + total matched documents in foreign collection)
+    assert.eq(localDocCount + localDocCount, curScannedObjects);
+
+    // Number of keys scanned in the foreign collection should be equal number of keys in local
+    // collection.
+    assert.eq(localDocCount, curScannedKeys);
+};
+
+insertDocumentToCollection(fromColl, foreignDocCount, "foreignField");
+insertDocumentToCollection(localColl, localDocCount, "localField");
+
+testQueryExecutorStatsWithCollectionScan();
+testQueryExecutorStatsWithIndexScan();
+}());