SERVER-41697 Remove the 'ns' field from any existing index spec catalog entries during upgrade

Author: GWlodarek

jstests/multiVersion/remove_ns_field_in_index_spec.js

@@ -0,0 +1,77 @@
+/**
+ * Tests that the 'ns' field in index specs is removed during metadata changes when in FCV 4.4.
+ *
+ * Starting in 4.4, the 'ns' field for index specs is no longer generated. We want to ensure that
+ * index specs created in prior server versions have their 'ns' field removed when running in FCV
+ * 4.4.
+ */
+(function() {
+'use strict';
+load('jstests/libs/feature_compatibility_version.js');
+
+const dbName = 'test';
+const collName = 'coll';
+
+const dbpath = MongoRunner.dataPath + 'remove_ns_field_in_index_spec';
+resetDbpath(dbpath);
+
+const mongodOptions42 =
+    Object.extend({binVersion: 'last-stable'}, {dbpath: dbpath, cleanData: false});
+const mongodOptions44 = Object.extend({binVersion: 'latest'}, {dbpath: dbpath, cleanData: false});
+
+/**
+ * Start up with the 4.2 binary and create a collection. The default '_id' index should have the
+ * 'ns' field present in its index spec.
+ */
+let conn = MongoRunner.runMongod(mongodOptions42);
+assert.neq(null, conn, 'mongod was unable to start with version ' + tojson(mongodOptions42));
+
+let testDb = conn.getDB(dbName);
+assert.commandWorked(testDb.adminCommand({setFeatureCompatibilityVersion: lastStableFCV}));
+assert.commandWorked(testDb.createCollection(collName));
+
+let coll = testDb.getCollection(collName);
+let indexes = coll.getIndexes();
+
+assert.eq(1, indexes.length);
+assert.eq(dbName + '.' + collName, indexes[0].ns);
+
+MongoRunner.stopMongod(conn);
+
+/**
+ * Restart with the 4.4 binary while in FCV 4.2. The index should not lose its 'ns' field when doing
+ * a disk modifying metadata change.
+ */
+let restartOpts44 = Object.extend(mongodOptions44, {restart: true});
+conn = MongoRunner.runMongod(restartOpts44);
+assert.neq(null, conn, 'mongod was unable to start with version ' + tojson(restartOpts44));
+
+testDb = conn.getDB(dbName);
+coll = testDb.getCollection(collName);
+
+// Run a metadata changing operation.
+assert.commandWorked(coll.createIndex({x: 1}));
+assert.commandWorked(coll.dropIndex({x: 1}));
+
+indexes = coll.getIndexes();
+
+assert.eq(1, indexes.length);
+assert.eq(dbName + '.' + collName, indexes[0].ns);
+
+/**
+ * Set the FCV to 4.4. The index should lose its 'ns' field when doing a disk modifying metadata
+ * change.
+ */
+assert.commandWorked(testDb.adminCommand({setFeatureCompatibilityVersion: latestFCV}));
+
+// Run a metadata changing operation.
+assert.commandWorked(coll.createIndex({x: 1}));
+assert.commandWorked(coll.dropIndex({x: 1}));
+
+indexes = coll.getIndexes();
+
+assert.eq(1, indexes.length);
+assert.eq(false, indexes[0].hasOwnProperty('ns'));
+
+MongoRunner.stopMongod(conn);
+})();

src/mongo/db/storage/SConscript

@@ -426,6 +426,7 @@ env.Library(
     ],
     LIBDEPS_PRIVATE=[
         '$BUILD_DIR/mongo/db/catalog/index_timestamp_helper',
+        '$BUILD_DIR/mongo/db/server_options_core',
     ],
 )
 

src/mongo/db/storage/durable_catalog_impl.cpp

@@ -42,6 +42,7 @@
 #include "mongo/db/index/index_descriptor.h"
 #include "mongo/db/namespace_string.h"
 #include "mongo/db/operation_context.h"
+#include "mongo/db/server_options.h"
 #include "mongo/db/storage/durable_catalog_feature_tracker.h"
 #include "mongo/db/storage/kv/kv_engine.h"
 #include "mongo/db/storage/record_store.h"
@@ -576,6 +577,17 @@ void DurableCatalogImpl::putMetaData(OperationContext* opCtx,
     BSONObj obj = _findEntry(opCtx, nss, &loc);
 
     {
+        // Remove the index spec 'ns' field if FCV is set to 4.4.
+        if (serverGlobalParams.featureCompatibility.isVersionInitialized() &&
+            serverGlobalParams.featureCompatibility.getVersion() ==
+                ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44) {
+            for (size_t i = 0; i < md.indexes.size(); i++) {
+                if (md.indexes[i].spec.hasField("ns")) {
+                    md.indexes[i].spec = md.indexes[i].spec.removeField("ns");
+                }
+            }
+        }
+
         // rebuilt doc
         BSONObjBuilder b;
         b.append("md", md.toBSON());