SERVER-54064 Clear out the logical session cache on refresh in arbiters

3 files changed, 66 insertions, 7 deletions

diff --git a/jstests/noPassthrough/server54064.js b/jstests/noPassthrough/server54064.js
new file mode 100644
index 00000000000..e08449a79bf
--- /dev/null
+++ b/jstests/noPassthrough/server54064.js
@@ -0,0 +1,60 @@
+/**
+ * Assert that arbiters periodically clear out their logical session cache. Inability to do so
+ * prohibits new clients from connecting.
+ *
+ * @tags: [requires_replication]
+ */
+(function() {
+    const name = "server54064";
+    const replSet = new ReplSetTest({
+        name: name,
+        nodes: 2,
+        // `disableLogicalSessionCacheRefresh` is true by default, but is disabled for testing
+        // purposes
+        // in servers spawned from the shell.
+        nodeOptions: {
+            setParameter: {
+                // Each refresh on an arbiter will empty the cache.
+                logicalSessionRefreshMillis: 10000,
+                // The number of connections/sessions before the cache is full, prohibiting new
+                // clients
+                // from connecting.
+                maxSessions: 3,
+                disableLogicalSessionCacheRefresh: false
+            }
+        }
+    });
+    const nodes = replSet.nodeList();
+
+    replSet.startSet();
+    replSet.initiate({
+        _id: name,
+        members: [{_id: 0, host: nodes[0]}, {_id: 1, host: nodes[1], arbiterOnly: true}],
+    });
+
+    let arbConn = replSet.getArbiter();
+    assert.soon(() => {
+        // Connect to mongo in a tight loop to exhaust the number of available logical sessions in
+        // the
+        // cache.
+        const result = new Mongo(arbConn.host).adminCommand({hello: 1});
+        if (result['ok'] === 0) {
+            assert.commandFailedWithCode(result, ErrorCodes.TooManyLogicalSessions);
+            return true;
+        }
+        return false;
+    });
+
+    assert.soon(() => {
+        // Once we observe that the number of sessions is maxed out, loop again to confirm that the
+        // cache eventually does get cleared.
+        const result = new Mongo(arbConn.host).adminCommand({hello: 1});
+        if (result['ok'] === 0) {
+            assert.commandFailedWithCode(result, ErrorCodes.TooManyLogicalSessions);
+            return false;
+        }
+        return true;
+    });
+
+    replSet.stopSet();
+})();
diff --git a/src/mongo/db/logical_session_cache_impl.cpp b/src/mongo/db/logical_session_cache_impl.cpp
index f59be6f4bef..40f015940f8 100644
--- a/src/mongo/db/logical_session_cache_impl.cpp
+++ b/src/mongo/db/logical_session_cache_impl.cpp
@@ -250,12 +250,7 @@ Status LogicalSessionCacheImpl::_reap(Client* client) {
             StringData notSetUpWarning =
                 "Sessions collection is not set up; "
                 "waiting until next sessions reap interval";
-            if (existsStatus.code() != ErrorCodes::NamespaceNotFound ||
-                existsStatus.code() != ErrorCodes::NamespaceNotSharded) {
-                log() << notSetUpWarning << ": " << existsStatus.reason();
-            } else {
-                log() << notSetUpWarning;
-            }
+            log() << notSetUpWarning << ": " << existsStatus.reason();
 
             return Status::OK();
         }
@@ -299,6 +294,8 @@ void LogicalSessionCacheImpl::_refresh(Client* client) {
 
     const auto replCoord = repl::ReplicationCoordinator::get(opCtx);
     if (replCoord && replCoord->isReplEnabled() && replCoord->getMemberState().arbiter()) {
+        stdx::lock_guard<stdx::mutex> lk(_mutex);
+        _activeSessions.clear();
         return;
     }
 
diff --git a/src/mongo/shell/servers.js b/src/mongo/shell/servers.js
index 51c016b146d..7c873be9f0c 100644
--- a/src/mongo/shell/servers.js
+++ b/src/mongo/shell/servers.js
@@ -1106,7 +1106,9 @@ var MongoRunner, _startMongod, startMongoProgram, runMongoProgram, startMongoPro
                 }
 
                 // Disable background cache refreshing to avoid races in tests
-                argArray.push(...['--setParameter', "disableLogicalSessionCacheRefresh=true"]);
+                if (!argArrayContainsSetParameterValue('disableLogicalSessionCacheRefresh=')) {
+                    argArray.push(...['--setParameter', "disableLogicalSessionCacheRefresh=true"]);
+                }
             }
 
             // Since options may not be backward compatible, mongos options are not