SERVER-26741 Retain temp collections when node restarted w/o --replSet.

Fixes an issue where temporary collections would be dropped after a
replica set member was restarted as a stand-alone mongod.

(cherry picked from commit 43e9c303c08f73b56490b662b3d11988cafafdf4)

2 files changed, 96 insertions, 4 deletions

diff --git a/jstests/replsets/temp_namespace_restart_as_standalone.js b/jstests/replsets/temp_namespace_restart_as_standalone.js
new file mode 100644
index 00000000000..063b1f3bbf4
--- /dev/null
+++ b/jstests/replsets/temp_namespace_restart_as_standalone.js
@@ -0,0 +1,87 @@
+/**
+ * Tests that temporary collections are not dropped when a member of a replica set is started up as
+ * a stand-alone mongod, i.e. without the --replSet parameter.
+ *
+ * @tags: [requires_persistence]
+ */
+(function() {
+    var rst = new ReplSetTest({nodes: 2});
+    rst.startSet();
+
+    // Rig the election so that the first node becomes the primary and remains primary despite the
+    // secondary being terminated during this test.
+    var replSetConfig = rst.getReplSetConfig();
+    replSetConfig.members[1].priority = 0;
+    replSetConfig.members[1].votes = 0;
+    rst.initiate(replSetConfig);
+
+    var primaryConn = rst.getPrimary();
+    var secondaryConn = rst.getSecondary();
+
+    var primaryDB = primaryConn.getDB("test");
+    var secondaryDB = secondaryConn.getDB("test");
+
+    // Create a temporary collection and wait until the operation has replicated to the secondary.
+    assert.commandWorked(primaryDB.runCommand({
+        create: "temp_collection",
+        temp: true,
+    }));
+
+    // Verify that the temporary collection exists on the primary and has temp=true.
+    var primaryCollectionInfos = primaryDB.getCollectionInfos({name: "temp_collection"});
+    assert.eq(1, primaryCollectionInfos.length, "'temp_collection' wasn't created on the primary");
+    assert.eq("temp_collection",
+              primaryCollectionInfos[0].name,
+              "'temp_collection' wasn't created on the primary");
+    assert.eq(true,
+              primaryCollectionInfos[0].options.temp,
+              "'temp_collection' wasn't created as temporary on the primary: " +
+                  tojson(primaryCollectionInfos[0].options));
+
+    rst.awaitReplication();
+
+    // Verify that the temporary collection exists on the secondary and has temp=true.
+    var secondaryCollectionInfos = secondaryDB.getCollectionInfos({name: "temp_collection"});
+    assert.eq(
+        1, secondaryCollectionInfos.length, "'temp_collection' wasn't created on the secondary");
+    assert.eq("temp_collection",
+              secondaryCollectionInfos[0].name,
+              "'temp_collection' wasn't created on the secondary");
+    assert.eq(true,
+              secondaryCollectionInfos[0].options.temp,
+              "'temp_collection' wasn't created as temporary on the secondary: " +
+                  tojson(secondaryCollectionInfos[0].options));
+
+    // Shut down the secondary and restart it as a stand-alone mongod.
+    var secondaryNodeId = rst.getNodeId(secondaryDB.getMongo());
+    rst.stop(secondaryNodeId);
+
+    secondaryConn = MongoRunner.runMongod({dbpath: secondaryConn.dbpath, noCleanData: true});
+    assert.neq(null, secondaryConn, "secondary failed to start up as a stand-alone mongod");
+    secondaryDB = secondaryConn.getDB("test");
+
+    // Verify that the temporary collection still exists on the secondary and has temp=true.
+    secondaryCollectionInfos = secondaryDB.getCollectionInfos({name: "temp_collection"});
+    assert.eq(1,
+              secondaryCollectionInfos.length,
+              "'temp_collection' was dropped after restarting the secondary as a stand-alone");
+    assert.eq("temp_collection",
+              secondaryCollectionInfos[0].name,
+              "'temp_collection' was dropped after restarting the secondary as a stand-alone");
+    assert.eq(true,
+              secondaryCollectionInfos[0].options.temp,
+              "'temp_collection' is no longer temporary after restarting the secondary as a" +
+                  " stand-alone: " + tojson(secondaryCollectionInfos[0].options));
+
+    // Shut down the secondary and restart it as a member of the replica set.
+    MongoRunner.stopMongod(secondaryConn);
+
+    var restart = true;
+    rst.start(secondaryNodeId, {}, restart);
+
+    // Verify that writes are replicated to the temporary collection and can successfully be applied
+    // by the secondary after having restarted it.
+    assert.writeOK(primaryDB.temp_collection.insert({}, {writeConcern: {w: 2, wtimeout: 60000}}));
+
+    rst.stopSet();
+})();
diff --git a/src/mongo/db/db.cpp b/src/mongo/db/db.cpp
index f5346915216..6b0dda65150 100644
--- a/src/mongo/db/db.cpp
+++ b/src/mongo/db/db.cpp
@@ -152,6 +152,7 @@ extern int diagLogging;
 namespace {
 
 const NamespaceString startupLogCollectionName("local.startup_log");
+const NamespaceString kSystemReplSetCollection("local.system.replset");
 
 #ifdef _WIN32
 ntservice::NtServiceDefaultStrings defaultServiceStrings = {
@@ -296,12 +297,9 @@ void checkForIdIndexes(OperationContext* txn, Database* db) {
  *          --replset.
  */
 unsigned long long checkIfReplMissingFromCommandLine(OperationContext* txn) {
-    // This is helpful for the query below to work as you can't open files when readlocked
-    ScopedTransaction transaction(txn, MODE_X);
-    Lock::GlobalWrite lk(txn->lockState());
     if (!repl::getGlobalReplicationCoordinator()->getSettings().usingReplSets()) {
         DBDirectClient c(txn);
-        return c.count("local.system.replset");
+        return c.count(kSystemReplSetCollection.ns());
     }
     return 0;
 }
@@ -414,6 +412,13 @@ void repairDatabasesAndCheckVersion(OperationContext* txn) {
 
     const repl::ReplSettings& replSettings = repl::getGlobalReplicationCoordinator()->getSettings();
 
+    // We open the "local" database before calling checkIfReplMissingFromCommandLine() to ensure the
+    // in-memory catalog entries for the 'kSystemReplSetCollection' collection have been populated
+    // if the collection exists. If the "local" database didn't exist at this point yet, then it
+    // will be created.
+    Lock::DBLock dbLock(txn->lockState(), kSystemReplSetCollection.db(), MODE_X);
+    dbHolder().openDb(txn, kSystemReplSetCollection.db());
+
     // On replica set members we only clear temp collections on DBs other than "local" during
     // promotion to primary. On pure slaves, they are only cleared when the oplog tells them
     // to. The local DB is special because it is not replicated.  See SERVER-10927 for more