SERVER-21168 Update top on database drop

4 files changed, 46 insertions, 5 deletions

diff --git a/jstests/noPassthroughWithMongod/top_drop.js b/jstests/noPassthroughWithMongod/top_drop.js
new file mode 100644
index 00000000000..e31129b4a4d
--- /dev/null
+++ b/jstests/noPassthroughWithMongod/top_drop.js
@@ -0,0 +1,35 @@
+/**
+ * Checks that top removes entries after dropping a collection or database.
+ * TODO(SERVER-21167): Move this test from noPassthrough to core.
+ */
+(function() {
+    let topDB = db.getSiblingDB("topdrop");
+    assert.commandWorked(topDB.dropDatabase());
+
+    // Asserts that the output of top contains exactly these collection entries for topDB.
+    function checkTopEntries(expectedEntries) {
+        let res = topDB.adminCommand("top");
+        assert.commandWorked(res);
+        let namesFromTotals = Object.keys(res.totals).filter(function(ns) {
+            return ns.startsWith(topDB.getName() + ".");
+        });
+        let expectedEntryNames = expectedEntries.map(function(coll) {
+            return coll.getFullName();
+        });
+        assert.eq(namesFromTotals.sort(), expectedEntryNames.sort());
+    }
+
+    // Create a few entries in top.
+    assert.writeOK(topDB.coll1.insert({}));
+    assert.writeOK(topDB.coll2.insert({}));
+    assert.writeOK(topDB.coll3.insert({}));
+    checkTopEntries([topDB.coll1, topDB.coll2, topDB.coll3]);
+
+    // Check that dropping a collection removes that collection but leaves the others.
+    assert.commandWorked(topDB.runCommand({drop: "coll3"}));
+    checkTopEntries([topDB.coll1, topDB.coll2]);
+
+    // Check that dropping the database removes the remaining collections.
+    assert.commandWorked(topDB.dropDatabase());
+    checkTopEntries([]);
+}());
diff --git a/src/mongo/db/catalog/database.cpp b/src/mongo/db/catalog/database.cpp
index 8f88ff86e31..41746be60ef 100644
--- a/src/mongo/db/catalog/database.cpp
+++ b/src/mongo/db/catalog/database.cpp
@@ -632,6 +632,10 @@ void Database::dropDatabase(OperationContext* txn, Database* db) {
 
     audit::logDropDatabase(txn->getClient(), name);
 
+    for (auto&& coll : *db) {
+        Top::get(txn->getClient()->getServiceContext()).collectionDropped(coll->ns().ns(), true);
+    }
+
     dbHolder().close(txn, name);
     db = NULL;  // d is now deleted
 
diff --git a/src/mongo/db/stats/top.cpp b/src/mongo/db/stats/top.cpp
index 30e47a6e1be..8bfe3431f6d 100644
--- a/src/mongo/db/stats/top.cpp
+++ b/src/mongo/db/stats/top.cpp
@@ -84,8 +84,6 @@ void Top::record(OperationContext* txn,
         return;
 
     auto hashedNs = UsageMap::HashedKey(ns);
-
-    // cout << "record: " << ns << "\t" << op << "\t" << command << endl;
     stdx::lock_guard<SimpleMutex> lk(_lock);
 
     if ((command || logicalOp == LogicalOp::opQuery) && ns == _lastDropped) {
@@ -142,10 +140,14 @@ void Top::_record(OperationContext* txn,
     }
 }
 
-void Top::collectionDropped(StringData ns) {
+void Top::collectionDropped(StringData ns, bool databaseDropped) {
     stdx::lock_guard<SimpleMutex> lk(_lock);
     _usage.erase(ns);
-    _lastDropped = ns.toString();
+    if (!databaseDropped) {
+        // If a collection drop occurred, there will be a subsequent call to record for this
+        // collection namespace which must be ignored. This does not apply to a database drop.
+        _lastDropped = ns.toString();
+    }
 }
 
 void Top::cloneMap(Top::UsageMap& out) const {
diff --git a/src/mongo/db/stats/top.h b/src/mongo/db/stats/top.h
index a7d543e0ae0..c613a624e4d 100644
--- a/src/mongo/db/stats/top.h
+++ b/src/mongo/db/stats/top.h
@@ -99,7 +99,7 @@ public:
 
     void cloneMap(UsageMap& out) const;
 
-    void collectionDropped(StringData ns);
+    void collectionDropped(StringData ns, bool databaseDropped = false);
 
     /**
      * Appends the collection-level latency statistics