From f13d685ade22d662070bde942eb094790d4e7b8d Mon Sep 17 00:00:00 2001
From: Blake Oler <blake.oler@mongodb.com>
Date: Thu, 1 Nov 2018 12:14:56 -0400
Subject: SERVER-37624 Allow sessions collection TTL index expiration value to
 change upon node restart

---
 src/mongo/db/sessions_collection_standalone.cpp | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

(limited to 'src/mongo/db/sessions_collection_standalone.cpp')

diff --git a/src/mongo/db/sessions_collection_standalone.cpp b/src/mongo/db/sessions_collection_standalone.cpp
index 3a45269070e..a29323817bd 100644
--- a/src/mongo/db/sessions_collection_standalone.cpp
+++ b/src/mongo/db/sessions_collection_standalone.cpp
@@ -47,8 +47,20 @@ BSONObj lsidQuery(const LogicalSessionId& lsid) {
 }  // namespace
 
 Status SessionsCollectionStandalone::setupSessionsCollection(OperationContext* opCtx) {
+    auto existsStatus = checkSessionsCollectionExists(opCtx);
+    if (existsStatus.isOK()) {
+        return Status::OK();
+    }
+
     DBDirectClient client(opCtx);
-    auto cmd = generateCreateIndexesCmd();
+    BSONObj cmd;
+
+    if (existsStatus.code() == ErrorCodes::IndexOptionsConflict) {
+        cmd = generateCollModCmd();
+    } else {
+        cmd = generateCreateIndexesCmd();
+    }
+
     BSONObj info;
     if (!client.runCommand(NamespaceString::kLogicalSessionsNamespace.db().toString(), cmd, info)) {
         return getStatusFromCommandResult(info);
@@ -66,15 +78,22 @@ Status SessionsCollectionStandalone::checkSessionsCollectionExists(OperationCont
         return Status{ErrorCodes::NamespaceNotFound, "config.system.sessions does not exist"};
     }
 
-    auto indexExists = std::find_if(indexes.begin(), indexes.end(), [](const BSONObj& index) {
+    auto index = std::find_if(indexes.begin(), indexes.end(), [](const BSONObj& index) {
         return index.getField("name").String() == kSessionsTTLIndex;
     });
 
-    if (indexExists == indexes.end()) {
+    if (index == indexes.end()) {
         return Status{ErrorCodes::IndexNotFound,
                       "config.system.sessions does not have the required TTL index"};
     };
 
+    if (!index->hasField("expireAfterSeconds") ||
+        index->getField("expireAfterSeconds").Int() != (localLogicalSessionTimeoutMinutes * 60)) {
+        return Status{
+            ErrorCodes::IndexOptionsConflict,
+            "config.system.sessions currently has the incorrect timeout for the TTL index"};
+    }
+
     return Status::OK();
 }
 
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