SERVER-20520 Include index key in $indexStats return documents

8 files changed, 55 insertions, 21 deletions

diff --git a/jstests/core/index_stats.js b/jstests/core/index_stats.js
index f2f913b3235..1fc028fca31 100644
--- a/jstests/core/index_stats.js
+++ b/jstests/core/index_stats.js
@@ -17,6 +17,19 @@
         return undefined;
     }
 
+    var getIndexKey = function (indexName) {
+        var cursor = col.aggregate([{$indexStats: {}}]);
+        while (cursor.hasNext()) {
+            var doc = cursor.next();
+
+            if (doc.name === indexName) {
+                return doc.key;
+            }
+        }
+
+        return undefined;
+    }
+
     assert.writeOK(col.insert({a: 1, b: 1, c: 1}));
     assert.writeOK(col.insert({a: 2, b: 2, c: 2}));
     assert.writeOK(col.insert({a: 3, b: 3, c: 3}));
@@ -33,6 +46,7 @@
 
     // Confirm a stats object exists post index creation (with 0 count).
     assert.eq(countA, getUsageCount("a_1"));
+    assert.eq({a: 1}, getIndexKey("a_1"));
 
     // Confirm index stats tick on find().
     col.findOne({a: 1});
diff --git a/src/mongo/db/catalog/collection_info_cache.cpp b/src/mongo/db/catalog/collection_info_cache.cpp
index 9682ee40899..0f1e6409c4b 100644
--- a/src/mongo/db/catalog/collection_info_cache.cpp
+++ b/src/mongo/db/catalog/collection_info_cache.cpp
@@ -175,18 +175,20 @@ void CollectionInfoCache::init(OperationContext* txn) {
         _collection->getIndexCatalog()->getIndexIterator(txn, includeUnfinishedIndexes);
     while (ii.more()) {
         const IndexDescriptor* desc = ii.next();
-        _indexUsageTracker.registerIndex(desc->indexName());
+        _indexUsageTracker.registerIndex(desc->indexName(), desc->keyPattern());
     }
 
     rebuildIndexData(txn);
 }
 
-void CollectionInfoCache::addedIndex(OperationContext* txn, StringData indexName) {
+void CollectionInfoCache::addedIndex(OperationContext* txn, const IndexDescriptor* desc) {
     // Requires exclusive collection lock.
     invariant(txn->lockState()->isCollectionLockedForMode(_collection->ns().ns(), MODE_X));
+    invariant(desc);
 
     rebuildIndexData(txn);
-    _indexUsageTracker.registerIndex(indexName);
+
+    _indexUsageTracker.registerIndex(desc->indexName(), desc->keyPattern());
 }
 
 void CollectionInfoCache::droppedIndex(OperationContext* txn, StringData indexName) {
diff --git a/src/mongo/db/catalog/collection_info_cache.h b/src/mongo/db/catalog/collection_info_cache.h
index 46d3a9e1784..4c5b67ed880 100644
--- a/src/mongo/db/catalog/collection_info_cache.h
+++ b/src/mongo/db/catalog/collection_info_cache.h
@@ -38,6 +38,7 @@
 namespace mongo {
 
 class Collection;
+class IndexDescriptor;
 class OperationContext;
 
 /**
@@ -83,7 +84,7 @@ public:
      *
      * Must be called under exclusive collection lock.
      */
-    void addedIndex(OperationContext* txn, StringData indexName);
+    void addedIndex(OperationContext* txn, const IndexDescriptor* desc);
 
     /**
      * Deregister a newly-dropped index with the cache.  Must be called whenever an index is
diff --git a/src/mongo/db/catalog/index_catalog.cpp b/src/mongo/db/catalog/index_catalog.cpp
index d0da634ac21..8662eb0f906 100644
--- a/src/mongo/db/catalog/index_catalog.cpp
+++ b/src/mongo/db/catalog/index_catalog.cpp
@@ -414,7 +414,7 @@ void IndexCatalog::IndexBuildBlock::success() {
 
     entry->setIsReady(true);
 
-    collection->infoCache()->addedIndex(_txn, _indexName);
+    collection->infoCache()->addedIndex(_txn, desc);
 }
 
 namespace {
@@ -792,7 +792,7 @@ public:
 
     void rollback() final {
         _entries->add(_entry);
-        _collection->infoCache()->addedIndex(_txn, _entry->descriptor()->indexName());
+        _collection->infoCache()->addedIndex(_txn, _entry->descriptor());
     }
 
 private:
diff --git a/src/mongo/db/collection_index_usage_tracker.cpp b/src/mongo/db/collection_index_usage_tracker.cpp
index 10894bcfe6e..9b1d0e17b22 100644
--- a/src/mongo/db/collection_index_usage_tracker.cpp
+++ b/src/mongo/db/collection_index_usage_tracker.cpp
@@ -49,12 +49,12 @@ void CollectionIndexUsageTracker::recordIndexAccess(StringData indexName) {
     _indexUsageMap[indexName].accesses.fetchAndAdd(1);
 }
 
-void CollectionIndexUsageTracker::registerIndex(StringData indexName) {
+void CollectionIndexUsageTracker::registerIndex(StringData indexName, const BSONObj& indexKey) {
     invariant(!indexName.empty());
     dassert(_indexUsageMap.find(indexName) == _indexUsageMap.end());
 
     // Create map entry.
-    _indexUsageMap[indexName] = IndexUsageStats(_clockSource->now());
+    _indexUsageMap[indexName] = IndexUsageStats(_clockSource->now(), indexKey);
 }
 
 void CollectionIndexUsageTracker::unregisterIndex(StringData indexName) {
diff --git a/src/mongo/db/collection_index_usage_tracker.h b/src/mongo/db/collection_index_usage_tracker.h
index def45712aad..ad55c229972 100644
--- a/src/mongo/db/collection_index_usage_tracker.h
+++ b/src/mongo/db/collection_index_usage_tracker.h
@@ -30,6 +30,7 @@
 
 #include "mongo/base/disallow_copying.h"
 #include "mongo/base/string_data.h"
+#include "mongo/bson/bsonobj.h"
 #include "mongo/platform/atomic_word.h"
 #include "mongo/util/string_map.h"
 #include "mongo/util/time_support.h"
@@ -51,14 +52,18 @@ class CollectionIndexUsageTracker {
 public:
     struct IndexUsageStats {
         IndexUsageStats() = default;
-        explicit IndexUsageStats(Date_t now) : trackerStartTime(now) {}
+        explicit IndexUsageStats(Date_t now, const BSONObj& key)
+            : trackerStartTime(now), indexKey(key.getOwned()) {}
 
         IndexUsageStats(const IndexUsageStats& other)
-            : accesses(other.accesses.load()), trackerStartTime(other.trackerStartTime) {}
+            : accesses(other.accesses.load()),
+              trackerStartTime(other.trackerStartTime),
+              indexKey(other.indexKey) {}
 
         IndexUsageStats& operator=(const IndexUsageStats& other) {
             accesses.store(other.accesses.load());
             trackerStartTime = other.trackerStartTime;
+            indexKey = other.indexKey;
             return *this;
         }
 
@@ -67,6 +72,9 @@ public:
 
         // Date/Time that we started tracking index usage.
         Date_t trackerStartTime;
+
+        // An owned copy of the associated IndexDescriptor's index key.
+        BSONObj indexKey;
     };
 
     /**
@@ -87,7 +95,7 @@ public:
      * Add map entry for 'indexName' stats collection. Must be called under exclusive collection
      * lock.
      */
-    void registerIndex(StringData indexName);
+    void registerIndex(StringData indexName, const BSONObj& indexKey);
 
     /**
      * Erase statistics for index 'indexName'. Must be called under exclusive collection lock.
diff --git a/src/mongo/db/collection_index_usage_tracker_test.cpp b/src/mongo/db/collection_index_usage_tracker_test.cpp
index 39a31120903..5ce0988452c 100644
--- a/src/mongo/db/collection_index_usage_tracker_test.cpp
+++ b/src/mongo/db/collection_index_usage_tracker_test.cpp
@@ -29,6 +29,7 @@
 #include "mongo/platform/basic.h"
 
 #include "mongo/db/collection_index_usage_tracker.h"
+#include "mongo/db/jsobj.h"
 #include "mongo/unittest/unittest.h"
 #include "mongo/util/clock_source_mock.h"
 
@@ -65,7 +66,7 @@ TEST_F(CollectionIndexUsageTrackerTest, Empty) {
 
 // Test that recording of a single index hit is reflected in returned stats map.
 TEST_F(CollectionIndexUsageTrackerTest, SingleHit) {
-    getTracker()->registerIndex("foo");
+    getTracker()->registerIndex("foo", BSON("foo" << 1));
     getTracker()->recordIndexAccess("foo");
     CollectionIndexUsageMap statsMap = getTracker()->getUsageStats();
     ASSERT(statsMap.find("foo") != statsMap.end());
@@ -74,7 +75,7 @@ TEST_F(CollectionIndexUsageTrackerTest, SingleHit) {
 
 // Test that recording of multiple index hits are reflected in stats map.
 TEST_F(CollectionIndexUsageTrackerTest, MultipleHit) {
-    getTracker()->registerIndex("foo");
+    getTracker()->registerIndex("foo", BSON("foo" << 1));
     getTracker()->recordIndexAccess("foo");
     getTracker()->recordIndexAccess("foo");
     CollectionIndexUsageMap statsMap = getTracker()->getUsageStats();
@@ -82,18 +83,25 @@ TEST_F(CollectionIndexUsageTrackerTest, MultipleHit) {
     ASSERT_EQUALS(2, statsMap["foo"].accesses.loadRelaxed());
 }
 
+TEST_F(CollectionIndexUsageTrackerTest, IndexKey) {
+    getTracker()->registerIndex("foo", BSON("foo" << 1));
+    CollectionIndexUsageMap statsMap = getTracker()->getUsageStats();
+    ASSERT(statsMap.find("foo") != statsMap.end());
+    ASSERT_EQUALS(BSON("foo" << 1), statsMap["foo"].indexKey);
+}
+
 // Test that index registration generates an entry in the stats map.
 TEST_F(CollectionIndexUsageTrackerTest, Register) {
-    getTracker()->registerIndex("foo");
+    getTracker()->registerIndex("foo", BSON("foo" << 1));
     ASSERT_EQUALS(1U, getTracker()->getUsageStats().size());
-    getTracker()->registerIndex("bar");
+    getTracker()->registerIndex("bar", BSON("bar" << 1));
     ASSERT_EQUALS(2U, getTracker()->getUsageStats().size());
 }
 
 // Test that index deregistration results in removal of an entry from the stats map.
 TEST_F(CollectionIndexUsageTrackerTest, Deregister) {
-    getTracker()->registerIndex("foo");
-    getTracker()->registerIndex("bar");
+    getTracker()->registerIndex("foo", BSON("foo" << 1));
+    getTracker()->registerIndex("bar", BSON("bar" << 1));
     ASSERT_EQUALS(2U, getTracker()->getUsageStats().size());
     getTracker()->unregisterIndex("foo");
     ASSERT_EQUALS(1U, getTracker()->getUsageStats().size());
@@ -103,7 +111,7 @@ TEST_F(CollectionIndexUsageTrackerTest, Deregister) {
 
 // Test that index deregistration results in reset of the usage counter.
 TEST_F(CollectionIndexUsageTrackerTest, HitAfterDeregister) {
-    getTracker()->registerIndex("foo");
+    getTracker()->registerIndex("foo", BSON("foo" << 1));
     getTracker()->recordIndexAccess("foo");
     getTracker()->recordIndexAccess("foo");
     CollectionIndexUsageMap statsMap = getTracker()->getUsageStats();
@@ -114,7 +122,7 @@ TEST_F(CollectionIndexUsageTrackerTest, HitAfterDeregister) {
     statsMap = getTracker()->getUsageStats();
     ASSERT(statsMap.find("foo") == statsMap.end());
 
-    getTracker()->registerIndex("foo");
+    getTracker()->registerIndex("foo", BSON("foo" << 1));
     getTracker()->recordIndexAccess("foo");
     statsMap = getTracker()->getUsageStats();
     ASSERT(statsMap.find("foo") != statsMap.end());
@@ -123,7 +131,7 @@ TEST_F(CollectionIndexUsageTrackerTest, HitAfterDeregister) {
 
 // Test that index tracker start date/time is reset on index deregistration/registration.
 TEST_F(CollectionIndexUsageTrackerTest, DateTimeAfterDeregister) {
-    getTracker()->registerIndex("foo");
+    getTracker()->registerIndex("foo", BSON("foo" << 1));
     CollectionIndexUsageMap statsMap = getTracker()->getUsageStats();
     ASSERT(statsMap.find("foo") != statsMap.end());
     ASSERT_EQUALS(statsMap["foo"].trackerStartTime, getClockSource()->now());
@@ -135,7 +143,7 @@ TEST_F(CollectionIndexUsageTrackerTest, DateTimeAfterDeregister) {
     // Increment clock source so that a new index registration has different start time.
     getClockSource()->advance(stdx::chrono::milliseconds(1));
 
-    getTracker()->registerIndex("foo");
+    getTracker()->registerIndex("foo", BSON("foo" << 1));
     statsMap = getTracker()->getUsageStats();
     ASSERT(statsMap.find("foo") != statsMap.end());
     ASSERT_EQUALS(statsMap["foo"].trackerStartTime, getClockSource()->now());
diff --git a/src/mongo/db/pipeline/document_source_index_stats.cpp b/src/mongo/db/pipeline/document_source_index_stats.cpp
index 65edfaea37d..517a781a71b 100644
--- a/src/mongo/db/pipeline/document_source_index_stats.cpp
+++ b/src/mongo/db/pipeline/document_source_index_stats.cpp
@@ -52,6 +52,7 @@ boost::optional<Document> DocumentSourceIndexStats::getNext() {
         const auto& stats = _indexStatsIter->second;
         MutableDocument doc;
         doc["name"] = Value(_indexStatsIter->first);
+        doc["key"] = Value(stats.indexKey);
         doc["host"] = Value(_processName);
         doc["accesses"]["ops"] = Value(stats.accesses.loadRelaxed());
         doc["accesses"]["since"] = Value(stats.trackerStartTime);