1 files changed, 12 insertions, 9 deletions

diff --git a/src/mongo/db/logical_session_cache.cpp b/src/mongo/db/logical_session_cache.cpp
index 9ab51495f52..1c94e019ac3 100644
--- a/src/mongo/db/logical_session_cache.cpp
+++ b/src/mongo/db/logical_session_cache.cpp
@@ -145,8 +145,8 @@ Status LogicalSessionCache::startSession(LogicalSessionRecord authoritativeRecor
 }
 
 void LogicalSessionCache::_refresh() {
-    SessionList activeSessions;
-    SessionList deadSessions;
+    LogicalSessionIdSet activeSessions;
+    LogicalSessionIdSet deadSessions;
 
     auto now = _service->now();
 
@@ -164,9 +164,9 @@ void LogicalSessionCache::_refresh() {
     for (auto& it : cacheCopy) {
         auto record = it.second;
         if (!_isDead(record, now)) {
-            activeSessions.push_back(record.getLsid());
+            activeSessions.insert(record.getLsid());
         } else {
-            deadSessions.push_back(record.getLsid());
+            deadSessions.insert(record.getLsid());
         }
     }
 
@@ -190,25 +190,28 @@ void LogicalSessionCache::_refresh() {
                 // by another thread.
                 it->second.setLastUse(now);
             }
+
+            activeSessions.insert(lsid);
         }
     }
 
-    activeSessions.splice(activeSessions.begin(), serviceSessions);
-
     // Query into the sessions collection to do the refresh. If any sessions have
     // failed to refresh, it means their authoritative records were removed, and
     // we should remove such records from our cache as well.
     auto failedToRefresh = _sessionsColl->refreshSessions(std::move(activeSessions));
-    deadSessions.splice(deadSessions.begin(), failedToRefresh);
 
     // Prune any dead records out of the cache. Dead records are ones that failed to
     // refresh, or ones that have expired locally. We don't make an effort to check
     // if the locally-expired records still have live authoritative records in the
     // sessions collection. We also don't attempt to resurrect our expired records.
+    // However, we *do* keep records alive if they are active on the service.
     {
         stdx::unique_lock<stdx::mutex> lk(_cacheMutex);
-        for (auto deadId : deadSessions) {
-            _cache.erase(deadId);
+        for (auto deadId : failedToRefresh) {
+            auto it = serviceSessions.find(deadId);
+            if (it == serviceSessions.end()) {
+                _cache.erase(deadId);
+            }
         }
     }
 }