SERVER-39420 Remove in-memory boolean to indicate config.server.sessions collection set up

(cherry picked from commit 2c20db31fcd6a2a9ac02506d55794f9b234af0a6)

3 files changed, 19 insertions, 12 deletions

diff --git a/jstests/sharding/sessions_collection_auto_healing.js b/jstests/sharding/sessions_collection_auto_healing.js
index 61271bd8dc5..a9526628ee0 100644
--- a/jstests/sharding/sessions_collection_auto_healing.js
+++ b/jstests/sharding/sessions_collection_auto_healing.js
@@ -3,6 +3,8 @@ load('jstests/libs/sessions_collection.js');
 (function() {
     "use strict";
 
+    load("jstests/libs/collection_drop_recreate.js");  // For assert[Drop|Create]Collection.
+
     // This test makes assertions about the number of sessions, which are not compatible with
     // implicit sessions.
     TestData.disableImplicitSessions = true;
@@ -125,20 +127,34 @@ load('jstests/libs/sessions_collection.js');
         assert.eq(shardConfig.system.sessions.count(), 4, "did not flush mongos' sessions");
     }
 
-    // Test that if we drop the index on the sessions collection,
-    // refresh on neither the shard nor the config db heals it.
+    // Test that if we drop the index on the sessions collection, only a refresh on the config
+    // server heals it.
     {
         assert.commandWorked(shardConfig.system.sessions.dropIndex({lastUse: 1}));
 
         validateSessionsCollection(shard, true, false);
 
         assert.commandWorked(configAdmin.runCommand({refreshLogicalSessionCacheNow: 1}));
-        validateSessionsCollection(shard, true, false);
+        validateSessionsCollection(shard, true, true);
+
+        assert.commandWorked(shardConfig.system.sessions.dropIndex({lastUse: 1}));
 
         assert.commandWorked(shardAdmin.runCommand({refreshLogicalSessionCacheNow: 1}));
         validateSessionsCollection(shard, true, false);
     }
 
+    // Test that if we drop the collection, it will be recreated only by the config server.
+    {
+        assertDropCollection(mongosConfig, "system.sessions");
+        validateSessionsCollection(shard, false, false);
+
+        assert.commandWorked(shardAdmin.runCommand({refreshLogicalSessionCacheNow: 1}));
+        validateSessionsCollection(shard, false, false);
+
+        assert.commandWorked(configAdmin.runCommand({refreshLogicalSessionCacheNow: 1}));
+        validateSessionsCollection(shard, true, true);
+    }
+
     st.stop();
     rs.stopSet();
 
diff --git a/src/mongo/db/sessions_collection_config_server.cpp b/src/mongo/db/sessions_collection_config_server.cpp
index 8ae627f1b90..e1409361931 100644
--- a/src/mongo/db/sessions_collection_config_server.cpp
+++ b/src/mongo/db/sessions_collection_config_server.cpp
@@ -99,13 +99,6 @@ Status SessionsCollectionConfigServer::setupSessionsCollection(OperationContext*
 
     stdx::lock_guard<stdx::mutex> lk(_mutex);
     {
-        // Only try to set up this collection until we have done so successfully once.
-        // Note: if there is a config server election, it's possible that two different
-        // primaries could both run the createIndexes scatter-gather query; this is ok.
-        if (_collectionSetUp) {
-            return Status::OK();
-        }
-
         auto res = _shardCollectionIfNeeded(opCtx);
         if (!res.isOK()) {
             log() << "Failed to create config.system.sessions: " << res.reason()
@@ -119,7 +112,6 @@ Status SessionsCollectionConfigServer::setupSessionsCollection(OperationContext*
                   << "will try again on the next refresh interval";
         }
 
-        _collectionSetUp = true;
         return res;
     }
 }
diff --git a/src/mongo/db/sessions_collection_config_server.h b/src/mongo/db/sessions_collection_config_server.h
index 2e80ca90fca..9e687f9798f 100644
--- a/src/mongo/db/sessions_collection_config_server.h
+++ b/src/mongo/db/sessions_collection_config_server.h
@@ -66,7 +66,6 @@ private:
     Status _generateIndexesIfNeeded(OperationContext* opCtx);
 
     stdx::mutex _mutex;
-    bool _collectionSetUp{false};
 };
 
 }  // namespace mongo