From 9bd5e1f1de06b7d6f97030036a2d03424399b5d0 Mon Sep 17 00:00:00 2001
From: Benety Goh <benety@mongodb.com>
Date: Tue, 11 Jul 2017 13:09:35 -0400
Subject: [PATCH] SERVER-29373 relax index name constraint when doing two phase
 collection drops under non-mmapv1 storage engines

---
 .../replsets/drop_collections_two_phase.js    | 15 ++++++++++++
 src/mongo/db/catalog/database_impl.cpp        | 23 +++++++++++--------
 src/mongo/db/catalog/index_catalog_impl.cpp   | 17 +++++++++-----
 3 files changed, 40 insertions(+), 15 deletions(-)

diff --git a/jstests/replsets/drop_collections_two_phase.js b/jstests/replsets/drop_collections_two_phase.js
index fb35984704d9c..18d63f12a2407 100644
--- a/jstests/replsets/drop_collections_two_phase.js
+++ b/jstests/replsets/drop_collections_two_phase.js
@@ -60,6 +60,21 @@
     primaryDB.createCollection(collToDrop);
     replTest.awaitReplication();
 
+    // Two phase collection should handle long index names gracefully.
+    // MMAP imposes a hard limit on index namespaces so we have to drop indexes that are too long
+    // to store on disk after renaming the collection. See SERVER-29747.
+    // Other storage engines should allow the implicit index renames to proceed because these
+    // renamed indexes are internal and will not be visible to users (no risk of being exported to
+    // another storage engine).
+    // TODO: remove storage engine check when SERVER-29474 is completed.
+    var storageEngine = jsTest.options().storageEngine;
+    if (storageEngine !== 'mmapv1') {
+        var coll = primaryDB.getCollection(collToDrop);
+        var maxNsLength = 127;
+        var indexName = ''.pad(maxNsLength - (coll.getFullName() + '.$').length, true, 'a');
+        assert.commandWorked(coll.ensureIndex({a: 1}, {name: indexName}));
+    }
+
     // Pause application on secondary so that commit point doesn't advance, meaning that a dropped
     // collection on the primary will remain in 'drop-pending' state.
     jsTestLog("Pausing oplog application on the secondary node.");
diff --git a/src/mongo/db/catalog/database_impl.cpp b/src/mongo/db/catalog/database_impl.cpp
index e96bd7325d6d0..1141dab3c722b 100644
--- a/src/mongo/db/catalog/database_impl.cpp
+++ b/src/mongo/db/catalog/database_impl.cpp
@@ -511,16 +511,21 @@ Status DatabaseImpl::dropCollectionEvenIfSystem(OperationContext* opCtx,
         }
     }
 
-    // Check if drop-pending namespace is too long for the index names in the collection.
     auto dpns = fullns.makeDropPendingNamespace(dropOpTime);
-    auto status =
-        dpns.checkLengthForRename(collection->getIndexCatalog()->getLongestIndexNameLength(opCtx));
-    if (!status.isOK()) {
-        log() << "dropCollection: " << fullns
-              << " - cannot proceed with collection rename for pending-drop: " << status
-              << ". Dropping collection immediately.";
-        fassertStatusOK(40463, _finishDropCollection(opCtx, fullns, collection));
-        return Status::OK();
+
+    // MMAPv1 requires that index namespaces are subject to the same length constraints as indexes
+    // in collections that are not in a drop-pending state. Therefore, we check if the drop-pending
+    // namespace is too long for the index names in the collection.
+    if (opCtx->getServiceContext()->getGlobalStorageEngine()->isMmapV1()) {
+        auto status = dpns.checkLengthForRename(
+            collection->getIndexCatalog()->getLongestIndexNameLength(opCtx));
+        if (!status.isOK()) {
+            log() << "dropCollection: " << fullns
+                  << " - cannot proceed with collection rename for pending-drop: " << status
+                  << ". Dropping collection immediately.";
+            fassertStatusOK(40463, _finishDropCollection(opCtx, fullns, collection));
+            return Status::OK();
+        }
     }
 
     // Rename collection using drop-pending namespace generated from drop optime.
diff --git a/src/mongo/db/catalog/index_catalog_impl.cpp b/src/mongo/db/catalog/index_catalog_impl.cpp
index e9cfd3a4f0cac..40f2ecb1c0d7b 100644
--- a/src/mongo/db/catalog/index_catalog_impl.cpp
+++ b/src/mongo/db/catalog/index_catalog_impl.cpp
@@ -590,12 +590,17 @@ Status IndexCatalogImpl::_isSpecOk(OperationContext* opCtx, const BSONObj& spec)
     if (name.empty())
         return Status(ErrorCodes::CannotCreateIndex, "index name cannot be empty");
 
-    const std::string indexNamespace = IndexDescriptor::makeIndexNamespace(nss.ns(), name);
-    if (indexNamespace.length() > NamespaceString::MaxNsLen)
-        return Status(ErrorCodes::CannotCreateIndex,
-                      str::stream() << "namespace name generated from index name \""
-                                    << indexNamespace
-                                    << "\" is too long (127 byte max)");
+    // Drop pending collections are internal to the server and will not be exported to another
+    // storage engine. The indexes contained in these collections are not subject to the same
+    // namespace length constraints as the ones in created by users.
+    if (!nss.isDropPendingNamespace()) {
+        auto indexNamespace = IndexDescriptor::makeIndexNamespace(nss.ns(), name);
+        if (indexNamespace.length() > NamespaceString::MaxNsLen)
+            return Status(ErrorCodes::CannotCreateIndex,
+                          str::stream() << "namespace name generated from index name \""
+                                        << indexNamespace
+                                        << "\" is too long (127 byte max)");
+    }
 
     const BSONObj key = spec.getObjectField("key");
     const Status keyStatus = index_key_validate::validateKeyPattern(key, indexVersion);