SERVER-33272 Proactively close newly empty databases

5 files changed, 51 insertions, 3 deletions

diff --git a/src/mongo/db/catalog/collection_catalog.h b/src/mongo/db/catalog/collection_catalog.h
index f3886c3fea0..308c31173c5 100644
--- a/src/mongo/db/catalog/collection_catalog.h
+++ b/src/mongo/db/catalog/collection_catalog.h
@@ -216,7 +216,7 @@ public:
     void onCloseCatalog(OperationContext* opCtx);
 
     /**
-     * Puts the catatlog back in open state, removing the pre-close state. See onCloseCatalog.
+     * Puts the catalog back in open state, removing the pre-close state. See onCloseCatalog.
      *
      * Must be called with the global lock acquired in exclusive mode.
      */
@@ -226,6 +226,13 @@ public:
     iterator end() const;
 
     /**
+     * Returns whether the database contains any collections.
+     */
+    bool empty(StringData db) const {
+        return begin(db) == end();
+    }
+
+    /**
      * Lookup the name of a resource by its ResourceId. If there are multiple namespaces mapped to
      * the same ResourceId entry, we return the boost::none for those namespaces until there is
      * only one namespace in the set. If the ResourceId is not found, boost::none is returned.
diff --git a/src/mongo/db/catalog/collection_catalog_test.cpp b/src/mongo/db/catalog/collection_catalog_test.cpp
index 205a5647e75..0ae2f578d5f 100644
--- a/src/mongo/db/catalog/collection_catalog_test.cpp
+++ b/src/mongo/db/catalog/collection_catalog_test.cpp
@@ -64,8 +64,11 @@ public:
 
         auto collection = std::make_unique<CollectionMock>(nss);
         col = collection.get();
+        ASSERT_TRUE(catalog.empty(nss.db()));
+
         // Register dummy collection in catalog.
         catalog.registerCollection(colUUID, std::move(collection));
+        ASSERT_FALSE(catalog.empty(nss.db()));
     }
 
 protected:
diff --git a/src/mongo/db/catalog/drop_collection.cpp b/src/mongo/db/catalog/drop_collection.cpp
index b5f30ae2a3e..bcf17660ef4 100644
--- a/src/mongo/db/catalog/drop_collection.cpp
+++ b/src/mongo/db/catalog/drop_collection.cpp
@@ -34,6 +34,7 @@
 #include "mongo/db/catalog/drop_collection.h"
 
 #include "mongo/db/background.h"
+#include "mongo/db/catalog/database_holder.h"
 #include "mongo/db/catalog/index_catalog.h"
 #include "mongo/db/client.h"
 #include "mongo/db/concurrency/write_conflict_exception.h"
@@ -160,7 +161,7 @@ Status dropCollection(OperationContext* opCtx,
         log() << "Hanging drop collection before lock acquisition while fail point is set";
         MONGO_FAIL_POINT_PAUSE_WHILE_SET(hangDropCollectionBeforeLockAcquisition);
     }
-    return writeConflictRetry(opCtx, "drop", collectionName.ns(), [&] {
+    Status status = writeConflictRetry(opCtx, "drop", collectionName.ns(), [&] {
         AutoGetDb autoDb(opCtx, collectionName.db(), MODE_IX);
         Database* db = autoDb.getDb();
         if (!db) {
@@ -175,6 +176,29 @@ Status dropCollection(OperationContext* opCtx,
                 opCtx, db, collectionName, dropOpTime, systemCollectionMode, result);
         }
     });
+
+    if (!status.isOK()) {
+        return status;
+    }
+
+    // If this dropped the last collection in the database, we should close the database.
+    bool empty = CollectionCatalog::get(opCtx).empty(collectionName.db());
+    if (!empty) {
+        return Status::OK();
+    }
+
+    Lock::DBLock dbLock(opCtx, collectionName.db(), MODE_X);
+
+    // Double check that we're still empty. A new collection could've been created before we got the
+    // exclusive lock.
+    empty = CollectionCatalog::get(opCtx).empty(collectionName.db());
+    if (!empty) {
+        return Status::OK();
+    }
+
+    DatabaseHolder::get(opCtx)->close(opCtx, collectionName.db());
+
+    return Status::OK();
 }
 
 }  // namespace mongo
diff --git a/src/mongo/dbtests/plan_executor_invalidation_test.cpp b/src/mongo/dbtests/plan_executor_invalidation_test.cpp
index 61eedeab72f..7a62f40afb8 100644
--- a/src/mongo/dbtests/plan_executor_invalidation_test.cpp
+++ b/src/mongo/dbtests/plan_executor_invalidation_test.cpp
@@ -59,6 +59,10 @@ static const NamespaceString nss("unittests.PlanExecutorInvalidationTest");
 class PlanExecutorInvalidationTest : public unittest::Test {
 public:
     PlanExecutorInvalidationTest() : _client(&_opCtx) {
+        // Create an additional collection to prevent the database from closing when the other
+        // collection is dropped.
+        ASSERT_TRUE(_client.createCollection("unittests.PlanExecutorInvalidationTestUnused"));
+
         _ctx.reset(new dbtests::WriteContextForTests(&_opCtx, nss.ns()));
         _client.dropCollection(nss.ns());
 
@@ -67,6 +71,10 @@ public:
         }
     }
 
+    ~PlanExecutorInvalidationTest() {
+        _client.dropCollection("unittests.PlanExecutorInvalidationTestUnused");
+    }
+
     /**
      * Return a plan executor that is going over the collection in nss.ns().
      */
diff --git a/src/mongo/dbtests/rollbacktests.cpp b/src/mongo/dbtests/rollbacktests.cpp
index fd48e6f46a3..d5e69fce2f3 100644
--- a/src/mongo/dbtests/rollbacktests.cpp
+++ b/src/mongo/dbtests/rollbacktests.cpp
@@ -53,7 +53,7 @@ namespace {
 const auto kIndexVersion = IndexDescriptor::IndexVersion::kV2;
 
 void dropDatabase(OperationContext* opCtx, const NamespaceString& nss) {
-    Lock::GlobalWrite globalWriteLock(opCtx);
+    AutoGetDb autoDB(opCtx, nss.db(), MODE_X);
     auto databaseHolder = DatabaseHolder::get(opCtx);
     auto db = databaseHolder->getDb(opCtx, nss.db());
 
@@ -394,6 +394,12 @@ public:
                 assertGet(CollectionOptions::parse(BSONObj(), CollectionOptions::parseForCommand));
             ASSERT_OK(ctx.db()->userCreateNS(&opCtx, nss, collectionOptions, defaultIndexes));
             insertRecord(&opCtx, nss, oldDoc);
+
+            // Create an additional collection to prevent the database from closing when the other
+            // collection is dropped.
+            NamespaceString unusedCollectionNSS("unittests.rollback_replace_collection_unused");
+            ASSERT_OK(ctx.db()->userCreateNS(
+                &opCtx, unusedCollectionNSS, collectionOptions, defaultIndexes));
             uow.commit();
         }
         ASSERT(collectionExists(&opCtx, &ctx, nss.ns()));