SERVER-62941 Add oplog server status to FTDC

2 files changed, 30 insertions, 11 deletions

diff --git a/src/mongo/db/ftdc/ftdc_server.cpp b/src/mongo/db/ftdc/ftdc_server.cpp
index da7a6cbfcc5..c9bca99d8fd 100644
--- a/src/mongo/db/ftdc/ftdc_server.cpp
+++ b/src/mongo/db/ftdc/ftdc_server.cpp
@@ -210,6 +210,8 @@ public:
         // "defaultRWConcern" is excluded because it changes rarely and instead included in rotation
         // "mirroredReads" is included to append the number of mirror-able operations observed and
         // mirrored by this process in FTDC collections.
+        // "oplog" is included to append the earliest and latest optimes, which allow calculation of
+        // the oplog window.
 
         BSONObjBuilder commandBuilder;
         commandBuilder.append(kCommand, 1);
@@ -217,6 +219,7 @@ public:
         commandBuilder.append("timing", false);
         commandBuilder.append("defaultRWConcern", false);
         commandBuilder.append(MirrorMaestro::kServerStatusSectionName, true);
+        commandBuilder.append("oplog", true);
 
         // Exclude 'serverStatus.transactions.lastCommittedTransactions' because it triggers
         // frequent schema changes.
diff --git a/src/mongo/db/repl/replication_info.cpp b/src/mongo/db/repl/replication_info.cpp
index 3bb8c198deb..8d994dd93b2 100644
--- a/src/mongo/db/repl/replication_info.cpp
+++ b/src/mongo/db/repl/replication_info.cpp
@@ -273,25 +273,41 @@ public:
         }
 
         BSONObjBuilder result;
-        // TODO(siyuan) Output term of OpTime
         result.append("latestOptime", replCoord->getMyLastAppliedOpTime().getTimestamp());
 
-        auto earliestOplogTimestampFetch = [&] {
+        auto earliestOplogTimestampFetch = [&]() -> StatusWith<Timestamp> {
             AutoGetOplog oplogRead(opCtx, OplogAccessMode::kRead);
             if (!oplogRead.getCollection()) {
                 return StatusWith<Timestamp>(ErrorCodes::NamespaceNotFound, "oplog doesn't exist");
             }
-            return oplogRead.getCollection()->getRecordStore()->getEarliestOplogTimestamp(opCtx);
-        }();
 
-        if (earliestOplogTimestampFetch.getStatus() == ErrorCodes::OplogOperationUnsupported) {
-            // Falling back to use getSingleton if the storage engine does not support
-            // getEarliestOplogTimestamp.
-            BSONObj o;
-            if (Helpers::getSingleton(opCtx, NamespaceString::kRsOplogNamespace.ns().c_str(), o)) {
-                earliestOplogTimestampFetch = o["ts"].timestamp();
+            // Try to get the lock. If it's already locked, immediately return null timestamp.
+            Lock::GlobalLock lk(
+                opCtx, MODE_IS, Date_t::now(), Lock::InterruptBehavior::kLeaveUnlocked);
+            if (!lk.isLocked()) {
+                LOGV2_DEBUG(
+                    6294100, 2, "Failed to get global lock for oplog server status section");
+                return Timestamp();
             }
-        }
+
+            // Try getting earliest oplog timestamp using getEarliestOplogTimestamp
+            auto swEarliestOplogTimestamp =
+                oplogRead.getCollection()->getRecordStore()->getEarliestOplogTimestamp(opCtx);
+
+            if (swEarliestOplogTimestamp.getStatus() == ErrorCodes::OplogOperationUnsupported) {
+                // Falling back to use getSingleton if the storage engine does not support
+                // getEarliestOplogTimestamp.
+                // Note that getSingleton will take a global IS lock, but this won't block because
+                // we are already holding the global IS lock.
+                BSONObj o;
+                if (Helpers::getSingleton(
+                        opCtx, NamespaceString::kRsOplogNamespace.ns().c_str(), o)) {
+                    return o["ts"].timestamp();
+                }
+            }
+
+            return swEarliestOplogTimestamp;
+        }();
 
         uassert(
             17347, "Problem reading earliest entry from oplog", earliestOplogTimestampFetch.isOK());