Revert "SERVER-31174 Move the sessions collection to config.system.sessions"

This reverts commit ba1704f7cbc0b9a03a181df145f75f433a59b7df.

17 files changed, 101 insertions, 126 deletions

diff --git a/jstests/auth/lib/commands_lib.js b/jstests/auth/lib/commands_lib.js
index 6717e17e64d..90b8d1051f8 100644
--- a/jstests/auth/lib/commands_lib.js
+++ b/jstests/auth/lib/commands_lib.js
@@ -664,7 +664,7 @@ var authCommandsLib = {
           testname: "aggregate_listLocalSessions_allUsers_true",
           command: {aggregate: 1, pipeline: [{$listLocalSessions: {allUsers: true}}], cursor: {}},
           testcases: [{
-              runOnDb: "config",
+              runOnDb: adminDbName,
               roles:
                   {clusterAdmin: 1, clusterMonitor: 1, clusterManager: 1, root: 1, __system: 1}
           }],
@@ -684,7 +684,7 @@ var authCommandsLib = {
               cursor: {}
           },
           testcases: [{
-              runOnDb: "config",
+              runOnDb: adminDbName,
               roles:
                   {clusterAdmin: 1, clusterMonitor: 1, clusterManager: 1, root: 1, __system: 1}
           }]
@@ -696,7 +696,7 @@ var authCommandsLib = {
               pipeline: [{$listSessions: {allUsers: false}}],
               cursor: {}
           },
-          testcases: [{runOnDb: "config", roles: roles_all}]
+          testcases: [{runOnDb: adminDbName, roles: roles_all}]
         },
         {
           testname: "aggregate_lookup",
diff --git a/jstests/auth/list_all_sessions.js b/jstests/auth/list_all_sessions.js
index 2fd47476ee9..68053722323 100644
--- a/jstests/auth/list_all_sessions.js
+++ b/jstests/auth/list_all_sessions.js
@@ -7,11 +7,10 @@
     function runListAllSessionsTest(mongod) {
         assert(mongod);
         const admin = mongod.getDB("admin");
-        const config = mongod.getDB("config");
 
         const pipeline = [{'$listSessions': {allUsers: true}}];
         function listSessions() {
-            return config.system.sessions.aggregate(pipeline);
+            return admin.system.sessions.aggregate(pipeline);
         }
 
         admin.createUser({user: 'admin', pwd: 'pass', roles: jsTest.adminUserRoles});
@@ -20,7 +19,7 @@
         admin.logout();
 
         // Fail if we're not logged in.
-        assertErrorCode(config.system.sessions, pipeline, ErrorCodes.Unauthorized);
+        assertErrorCode(admin.system.sessions, pipeline, ErrorCodes.Unauthorized);
 
         // Start a new session and capture its sessionId.
         assert(admin.auth('user1', 'pass'));
@@ -29,11 +28,11 @@
         assert.commandWorked(admin.runCommand({refreshLogicalSessionCacheNow: 1}));
 
         // Ensure that a normal user can NOT listSessions{allUsers:true} to view their session.
-        assertErrorCode(config.system.sessions, pipeline, ErrorCodes.Unauthorized);
+        assertErrorCode(admin.system.sessions, pipeline, ErrorCodes.Unauthorized);
 
         // Ensure that a normal user can NOT listSessions to view others' sessions.
         const viewAdminPipeline = [{'$listSessions': {users: [{user: 'admin', db: 'admin'}]}}];
-        assertErrorCode(config.system.sessions, viewAdminPipeline, ErrorCodes.Unauthorized);
+        assertErrorCode(admin.system.sessions, viewAdminPipeline, ErrorCodes.Unauthorized);
 
         // Ensure that the cache now contains the session and is visible by admin
         assert(admin.auth('admin', 'pass'));
diff --git a/jstests/auth/list_sessions.js b/jstests/auth/list_sessions.js
index b130999a3ef..4647f6d75c7 100644
--- a/jstests/auth/list_sessions.js
+++ b/jstests/auth/list_sessions.js
@@ -7,11 +7,10 @@
     function runListSessionsTest(mongod) {
         assert(mongod);
         const admin = mongod.getDB('admin');
-        const config = mongod.getDB('config');
 
         const pipeline = [{'$listSessions': {}}];
         function listSessions() {
-            return config.system.sessions.aggregate(pipeline);
+            return admin.system.sessions.aggregate(pipeline);
         }
 
         admin.createUser({user: 'admin', pwd: 'pass', roles: jsTest.adminUserRoles});
@@ -22,7 +21,7 @@
         admin.logout();
 
         // Fail when not logged in.
-        assertErrorCode(config.system.sessions, pipeline, ErrorCodes.Unauthorized);
+        assertErrorCode(admin.system.sessions, pipeline, ErrorCodes.Unauthorized);
 
         // Start a new session and capture its sessionId.
         assert(admin.auth('user1', 'pass'));
@@ -40,7 +39,7 @@
         // Ask again using explicit UID.
         const user1Pipeline = [{'$listSessions': {users: [{user: "user1", db: "admin"}]}}];
         function listUser1Sessions() {
-            return config.system.sessions.aggregate(user1Pipeline);
+            return admin.system.sessions.aggregate(user1Pipeline);
         }
         const resultArrayMine = listUser1Sessions().toArray();
         assert.eq(bsonWoCompare(resultArray, resultArrayMine), 0);
@@ -53,14 +52,14 @@
         assert.eq(listSessions().toArray().length, 0);
 
         // Ensure users can't view either other's sessions.
-        assertErrorCode(config.system.sessions, user1Pipeline, ErrorCodes.Unauthorized);
+        assertErrorCode(admin.system.sessions, user1Pipeline, ErrorCodes.Unauthorized);
 
         if (true) {
             // TODO SERVER-29141: Support forcing pipelines to run on mongos
             return;
         }
         function listLocalSessions() {
-            return config.aggregate([{'$listLocalSessions': {}}]);
+            return admin.aggregate([{'$listLocalSessions': {}}]);
         }
         assert.eq(listLocalSessions().toArray().length, 0);
     }
diff --git a/jstests/core/list_all_sessions.js b/jstests/core/list_all_sessions.js
index cf36f1187dd..aef0ae33109 100644
--- a/jstests/core/list_all_sessions.js
+++ b/jstests/core/list_all_sessions.js
@@ -5,10 +5,9 @@
     load('jstests/aggregation/extras/utils.js');
 
     const admin = db.getSiblingDB("admin");
-    const config = db.getSiblingDB("config");
     const pipeline = [{'$listSessions': {allUsers: true}}];
     function listSessions() {
-        return config.system.sessions.aggregate(pipeline);
+        return admin.system.sessions.aggregate(pipeline);
     }
 
     // Start a new session and capture its sessionId.
diff --git a/jstests/core/list_sessions.js b/jstests/core/list_sessions.js
index e2b8adb5a78..0636377a3be 100644
--- a/jstests/core/list_sessions.js
+++ b/jstests/core/list_sessions.js
@@ -5,10 +5,9 @@
     load('jstests/aggregation/extras/utils.js');
 
     const admin = db.getSiblingDB('admin');
-    const config = db.getSiblingDB('config');
     const pipeline = [{'$listSessions': {}}];
     function listSessions() {
-        return config.system.sessions.aggregate(pipeline);
+        return admin.system.sessions.aggregate(pipeline);
     }
 
     // Start a new session and capture its sessionId.
@@ -48,7 +47,7 @@
         return {user: authUsers[0].user, db: authUsers[0].db};
     })();
     function listMySessions() {
-        return config.system.sessions.aggregate([{'$listSessions': {users: [myusername]}}]);
+        return admin.system.sessions.aggregate([{'$listSessions': {users: [myusername]}}]);
     }
     const myArray = listMySessions().toArray();
     assert.eq(resultArray.length, myArray.length);
diff --git a/jstests/noPassthrough/refresh_logical_session_cache_now.js b/jstests/noPassthrough/refresh_logical_session_cache_now.js
index 6d10cbca451..e3fe583f074 100644
--- a/jstests/noPassthrough/refresh_logical_session_cache_now.js
+++ b/jstests/noPassthrough/refresh_logical_session_cache_now.js
@@ -8,7 +8,6 @@
     // Start up a standalone server.
     var conn = MongoRunner.runMongod({nojournal: ""});
     var admin = conn.getDB("admin");
-    var config = conn.getDB("config");
 
     // Trigger an initial refresh, as a sanity check.
     res = admin.runCommand(refresh);
@@ -18,13 +17,13 @@
     res = admin.runCommand(startSession);
     assert.commandWorked(res, "unable to start session");
 
-    assert.eq(config.system.sessions.count(), 0, "should not have session records yet");
+    assert.eq(admin.system.sessions.count(), 0, "should not have session records yet");
 
     // Trigger a refresh. Session should now be in the collection.
     res = admin.runCommand(refresh);
     assert.commandWorked(res, "failed to refresh");
 
-    assert.eq(config.system.sessions.count(), 1, "should have written session records");
+    assert.eq(admin.system.sessions.count(), 1, "should have written session records");
 
     // Start some new sessions. Should not be in the collection yet.
     var numSessions = 100;
@@ -33,13 +32,13 @@
         assert.commandWorked(res, "unable to start session");
     }
 
-    assert.eq(config.system.sessions.count(), 1, "should not have more session records yet");
+    assert.eq(admin.system.sessions.count(), 1, "should not have more session records yet");
 
     // Trigger another refresh. All sessions should now be in the collection.
     res = admin.runCommand(refresh);
     assert.commandWorked(res, "failed to refresh");
 
     assert.eq(
-        config.system.sessions.count(), numSessions + 1, "should have written session records");
+        admin.system.sessions.count(), numSessions + 1, "should have written session records");
 
 }());
diff --git a/jstests/noPassthrough/refresh_sessions_command.js b/jstests/noPassthrough/refresh_sessions_command.js
index 80b249faca7..0c08d0891ce 100644
--- a/jstests/noPassthrough/refresh_sessions_command.js
+++ b/jstests/noPassthrough/refresh_sessions_command.js
@@ -37,14 +37,13 @@
     admin.auth("admin", "admin");
 
     result = admin.runCommand({
-        createRole: 'readSessionsCollection',
-        privileges: [{resource: {db: 'config', collection: 'system.sessions'}, actions: ['find']}],
+        createRole: 'readAdmin',
+        privileges: [{resource: {db: 'admin', collection: 'system.sessions'}, actions: ['find']}],
         roles: []
     });
-    assert.commandWorked(result, "couldn't make readSessionsCollection role");
+    assert.commandWorked(result, "couldn't make readAdmin role");
 
-    admin.createUser(
-        {user: 'readSessionsCollection', pwd: 'pwd', roles: ['readSessionsCollection']});
+    admin.createUser({user: 'readAdmin', pwd: 'pwd', roles: ['readAdmin']});
     admin.logout();
 
     // Test that we cannot run refreshSessions unauthenticated if --auth is on.
@@ -76,12 +75,10 @@
 
     // Test that once we force a refresh, all of these sessions are in the sessions collection.
     admin.logout();
-    admin.auth("readSessionsCollection", "pwd");
+    admin.auth("readAdmin", "pwd");
     result = admin.runCommand({refreshLogicalSessionCacheNow: 1});
     assert.commandWorked(result, "could not force refresh");
-
-    var config = conn.getDB("config");
-    assert.eq(config.system.sessions.count(), 3, "should have refreshed all session records");
+    assert.eq(admin.system.sessions.count(), 3, "should have refreshed all session records");
 
     MongoRunner.stopMongod(conn);
 })();
diff --git a/jstests/noPassthrough/system_indexes.js b/jstests/noPassthrough/system_indexes.js
index 95f9d90c4a2..dd27ea4a92d 100644
--- a/jstests/noPassthrough/system_indexes.js
+++ b/jstests/noPassthrough/system_indexes.js
@@ -6,7 +6,6 @@
 
 (function() {
     let conn = MongoRunner.runMongod({smallfiles: ""});
-    let config = conn.getDB("config");
     let db = conn.getDB("admin");
 
     // TEST: User and role collections start off with no indexes
@@ -66,16 +65,15 @@
     assert.eq(2, db.system.roles.getIndexes().length);
 
     // TEST: Inserting to the sessions collection creates indexes
-    config = conn.getDB("config");
-    assert.eq(0, config.system.sessions.getIndexes().length);
-    config.system.sessions.insert({lastUse: new Date()});
-    assert.eq(2, config.system.sessions.getIndexes().length);
+    assert.eq(0, db.system.sessions.getIndexes().length);
+    db.system.sessions.insert({lastUse: new Date()});
+    assert.eq(2, db.system.sessions.getIndexes().length);
 
-    // TEST: Destroying config.system.sessions index and restarting will recreate it
-    assert.commandWorked(config.system.sessions.dropIndexes());
+    // TEST: Destroying admin.system.sessions index and restarting will recreate it
+    assert.commandWorked(db.system.sessions.dropIndexes());
     MongoRunner.stopMongod(conn);
     conn = MongoRunner.runMongod({restart: conn, cleanData: false});
-    config = conn.getDB("config");
-    assert.eq(2, config.system.sessions.getIndexes().length);
+    db = conn.getDB("admin");
+    assert.eq(2, db.system.sessions.getIndexes().length);
 
 })();
diff --git a/jstests/noPassthrough/verify_session_cache_updates.js b/jstests/noPassthrough/verify_session_cache_updates.js
index e2d51bd27e5..e9912144e6f 100644
--- a/jstests/noPassthrough/verify_session_cache_updates.js
+++ b/jstests/noPassthrough/verify_session_cache_updates.js
@@ -8,12 +8,12 @@
 
         function verify(conn, nRecords) {
             conn.getDB("admin").runCommand({refreshLogicalSessionCacheNow: 1});
-            assert.eq(nRecords, conn.getDB("config").system.sessions.find({}).count());
+            assert.eq(nRecords, conn.getDB("admin").system.sessions.find({}).count());
         }
 
         function getLastUse(conn) {
             conn.getDB("admin").runCommand({refreshLogicalSessionCacheNow: 1});
-            return conn.getDB("config").system.sessions.findOne({}).lastUse;
+            return conn.getDB("admin").system.sessions.findOne({}).lastUse;
         }
 
         // initially we have no sessions
diff --git a/jstests/replsets/refresh_sessions_rs.js b/jstests/replsets/refresh_sessions_rs.js
index cc44affe6a2..abb71e22534 100644
--- a/jstests/replsets/refresh_sessions_rs.js
+++ b/jstests/replsets/refresh_sessions_rs.js
@@ -5,7 +5,7 @@
     var startSession = {startSession: 1};
 
     // Start up a replica set.
-    var dbName = "config";
+    var dbName = "admin";
 
     var replTest = new ReplSetTest({name: 'refresh', nodes: 3});
     var nodes = replTest.startSet();
diff --git a/jstests/sharding/refresh_sessions.js b/jstests/sharding/refresh_sessions.js
index 1e2bac22c8e..0e575fe6a69 100644
--- a/jstests/sharding/refresh_sessions.js
+++ b/jstests/sharding/refresh_sessions.js
@@ -1,7 +1,7 @@
 (function() {
     "use strict";
 
-    var sessionsDb = "config";
+    var sessionsDb = "admin";
     var refresh = {refreshLogicalSessionCacheNow: 1};
     var startSession = {startSession: 1};
 
diff --git a/src/mongo/db/namespace_string.cpp b/src/mongo/db/namespace_string.cpp
index 035228b65ad..35fbde965dd 100644
--- a/src/mongo/db/namespace_string.cpp
+++ b/src/mongo/db/namespace_string.cpp
@@ -115,8 +115,7 @@ bool NamespaceString::isLegalClientSystemNS() const {
             return true;
         if (ns() == "admin.system.backup_users")
             return true;
-    } else if (db() == "config") {
-        if (ns() == "config.system.sessions")
+        if (ns() == "admin.system.sessions")
             return true;
     }
     if (ns() == "local.system.replset")
diff --git a/src/mongo/db/ops/insert.cpp b/src/mongo/db/ops/insert.cpp
index de02fda5642..0b422f8882c 100644
--- a/src/mongo/db/ops/insert.cpp
+++ b/src/mongo/db/ops/insert.cpp
@@ -235,6 +235,8 @@ Status userAllowedCreateNS(StringData db, StringData coll) {
         if (db == "admin") {
             if (coll == "system.version")
                 return Status::OK();
+            if (coll == "system.sessions")
+                return Status::OK();
             if (coll == "system.roles")
                 return Status::OK();
             if (coll == "system.new_users")
@@ -244,10 +246,6 @@ Status userAllowedCreateNS(StringData db, StringData coll) {
             if (coll == "system.keys")
                 return Status::OK();
         }
-        if (db == "config") {
-            if (coll == "system.sessions")
-                return Status::OK();
-        }
         if (db == "local") {
             if (coll == "system.replset")
                 return Status::OK();
diff --git a/src/mongo/db/pipeline/document_source_list_sessions.h b/src/mongo/db/pipeline/document_source_list_sessions.h
index 47c08af9d73..38ba2b21b67 100644
--- a/src/mongo/db/pipeline/document_source_list_sessions.h
+++ b/src/mongo/db/pipeline/document_source_list_sessions.h
@@ -37,7 +37,7 @@ namespace mongo {
 
 /**
  * $listSessions: { allUsers: true/false, users: [ {user:"jsmith", db:"test"}, ... ] }
- * Return all sessions in the config.system.sessions collection
+ * Return all sessions in the admin.system.sessions collection
  * or just sessions for the currently logged in user. (Default: false)
  *
  * This is essentially an alias for {$match:{"_id.uid": myid}} or {$match:{}}
diff --git a/src/mongo/db/sessions_collection.h b/src/mongo/db/sessions_collection.h
index 63fd34667cf..9d29924069c 100644
--- a/src/mongo/db/sessions_collection.h
+++ b/src/mongo/db/sessions_collection.h
@@ -49,9 +49,9 @@ class SessionsCollection {
 public:
     virtual ~SessionsCollection();
 
-    static constexpr StringData kSessionsDb = "config"_sd;
+    static constexpr StringData kSessionsDb = "admin"_sd;
     static constexpr StringData kSessionsCollection = "system.sessions"_sd;
-    static constexpr StringData kSessionsFullNS = "config.system.sessions"_sd;
+    static constexpr StringData kSessionsFullNS = "admin.system.sessions"_sd;
 
     static const NamespaceString kSessionsNamespaceString;
 
diff --git a/src/mongo/db/system_index.cpp b/src/mongo/db/system_index.cpp
index be95f1d0758..0c07a4e46ad 100644
--- a/src/mongo/db/system_index.cpp
+++ b/src/mongo/db/system_index.cpp
@@ -67,7 +67,7 @@ IndexSpec v3SystemUsersIndexSpec;
 IndexSpec v3SystemRolesIndexSpec;
 IndexSpec v1SystemSessionsIndexSpec;
 
-const NamespaceString sessionCollectionNamespace("config.system.sessions");
+const NamespaceString sessionCollectionNamespace("admin.system.sessions");
 
 MONGO_INITIALIZER(AuthIndexKeyPatterns)(InitializerContext*) {
     v1SystemUsersKeyPattern = BSON("user" << 1 << "userSource" << 1);
@@ -145,84 +145,72 @@ Status verifySystemIndexes(OperationContext* opCtx) {
     const NamespaceString& systemUsers = AuthorizationManager::usersCollectionNamespace;
     const NamespaceString& systemRoles = AuthorizationManager::rolesCollectionNamespace;
 
-    // Create indexes for collections on the admin db
-    {
-        AutoGetDb autoDb(opCtx, systemUsers.db(), MODE_X);
-        if (!autoDb.getDb()) {
-            return Status::OK();
-        }
-
-        Collection* collection = autoDb.getDb()->getCollection(opCtx, systemUsers);
-        if (collection) {
-            IndexCatalog* indexCatalog = collection->getIndexCatalog();
-            invariant(indexCatalog);
-
-            // Make sure the old unique index from v2.4 on system.users doesn't exist.
-            std::vector<IndexDescriptor*> indexes;
-            indexCatalog->findIndexesByKeyPattern(opCtx, v1SystemUsersKeyPattern, false, &indexes);
-
-            if (!indexes.empty()) {
-                fassert(ErrorCodes::AmbiguousIndexKeyPattern, indexes.size() == 1);
-                return Status(ErrorCodes::AuthSchemaIncompatible,
-                              "Old 2.4 style user index identified. "
-                              "The authentication schema needs to be updated by "
-                              "running authSchemaUpgrade on a 2.6 server.");
-            }
+    AutoGetDb autoDb(opCtx, systemUsers.db(), MODE_X);
+    if (!autoDb.getDb()) {
+        return Status::OK();
+    }
 
-            // Ensure that system indexes exist for the user collection
-            indexCatalog->findIndexesByKeyPattern(opCtx, v3SystemUsersKeyPattern, false, &indexes);
-            if (indexes.empty()) {
-                try {
-                    generateSystemIndexForExistingCollection(
-                        opCtx, collection, systemUsers, v3SystemUsersIndexSpec);
-                } catch (...) {
-                    return exceptionToStatus();
-                }
-            }
+    Collection* collection = autoDb.getDb()->getCollection(opCtx, systemUsers);
+    if (collection) {
+        IndexCatalog* indexCatalog = collection->getIndexCatalog();
+        invariant(indexCatalog);
+
+        // Make sure the old unique index from v2.4 on system.users doesn't exist.
+        std::vector<IndexDescriptor*> indexes;
+        indexCatalog->findIndexesByKeyPattern(opCtx, v1SystemUsersKeyPattern, false, &indexes);
+
+        if (!indexes.empty()) {
+            fassert(ErrorCodes::AmbiguousIndexKeyPattern, indexes.size() == 1);
+            return Status(ErrorCodes::AuthSchemaIncompatible,
+                          "Old 2.4 style user index identified. "
+                          "The authentication schema needs to be updated by "
+                          "running authSchemaUpgrade on a 2.6 server.");
         }
 
-        // Ensure that system indexes exist for the roles collection, if it exists.
-        collection = autoDb.getDb()->getCollection(opCtx, systemRoles);
-        if (collection) {
-            IndexCatalog* indexCatalog = collection->getIndexCatalog();
-            invariant(indexCatalog);
-
-            std::vector<IndexDescriptor*> indexes;
-            indexCatalog->findIndexesByKeyPattern(opCtx, v3SystemRolesKeyPattern, false, &indexes);
-            if (indexes.empty()) {
-                try {
-                    generateSystemIndexForExistingCollection(
-                        opCtx, collection, systemRoles, v3SystemRolesIndexSpec);
-                } catch (...) {
-                    return exceptionToStatus();
-                }
+        // Ensure that system indexes exist for the user collection
+        indexCatalog->findIndexesByKeyPattern(opCtx, v3SystemUsersKeyPattern, false, &indexes);
+        if (indexes.empty()) {
+            try {
+                generateSystemIndexForExistingCollection(
+                    opCtx, collection, systemUsers, v3SystemUsersIndexSpec);
+            } catch (...) {
+                return exceptionToStatus();
             }
         }
     }
 
-    // Create indexes for system collections in the config db.
-    {
-        AutoGetDb autoDb(opCtx, sessionCollectionNamespace.db(), MODE_X);
-        if (!autoDb.getDb()) {
-            return Status::OK();
+    // Ensure that system indexes exist for the roles collection, if it exists.
+    collection = autoDb.getDb()->getCollection(opCtx, systemRoles);
+    if (collection) {
+        IndexCatalog* indexCatalog = collection->getIndexCatalog();
+        invariant(indexCatalog);
+
+        std::vector<IndexDescriptor*> indexes;
+        indexCatalog->findIndexesByKeyPattern(opCtx, v3SystemRolesKeyPattern, false, &indexes);
+        if (indexes.empty()) {
+            try {
+                generateSystemIndexForExistingCollection(
+                    opCtx, collection, systemRoles, v3SystemRolesIndexSpec);
+            } catch (...) {
+                return exceptionToStatus();
+            }
         }
+    }
 
-        // Ensure that system indexes exist for the sessions collection, if it exists.
-        auto collection = autoDb.getDb()->getCollection(opCtx, sessionCollectionNamespace);
-        if (collection) {
-            IndexCatalog* indexCatalog = collection->getIndexCatalog();
-            invariant(indexCatalog);
-
-            std::vector<IndexDescriptor*> indexes;
-            indexCatalog->findIndexesByKeyPattern(
-                opCtx, v1SystemSessionsKeyPattern, false, &indexes);
-            if (indexes.empty()) {
-                try {
-                    generateSystemIndexForExistingCollection(
-                        opCtx, collection, sessionCollectionNamespace, v1SystemSessionsIndexSpec);
-                } catch (...) {
-                    return exceptionToStatus();
-                }
+    // Ensure that system indexes exist for the sessions collection, if it exists.
+    collection = autoDb.getDb()->getCollection(opCtx, sessionCollectionNamespace);
+    if (collection) {
+        IndexCatalog* indexCatalog = collection->getIndexCatalog();
+        invariant(indexCatalog);
+
+        std::vector<IndexDescriptor*> indexes;
+        indexCatalog->findIndexesByKeyPattern(opCtx, v1SystemSessionsKeyPattern, false, &indexes);
+        if (indexes.empty()) {
+            try {
+                generateSystemIndexForExistingCollection(
+                    opCtx, collection, sessionCollectionNamespace, v1SystemSessionsIndexSpec);
+            } catch (...) {
+                return exceptionToStatus();
             }
         }
     }
diff --git a/src/mongo/dbtests/logical_sessions_tests.cpp b/src/mongo/dbtests/logical_sessions_tests.cpp
index 0b1b42df660..13ca0c434c8 100644
--- a/src/mongo/dbtests/logical_sessions_tests.cpp
+++ b/src/mongo/dbtests/logical_sessions_tests.cpp
@@ -45,7 +45,7 @@
 namespace LogicalSessionTests {
 
 namespace {
-constexpr StringData kTestNS = "config.system.sessions"_sd;
+constexpr StringData kTestNS = "admin.system.sessions"_sd;
 
 LogicalSessionRecord makeRecord(Date_t time = Date_t::now()) {
     auto record = makeLogicalSessionRecordForTest();