SERVER-38588 block application of prepare oplog entry on secondaries when a concurrent background index build is running

This will prevent hybrid index builds from corrupting an index on secondary nodes if a prepared transaction becomes prepared during a build but commits after the index build commits.

1 files changed, 13 insertions, 0 deletions

diff --git a/src/mongo/db/repl/apply_ops.cpp b/src/mongo/db/repl/apply_ops.cpp
index 8c3bea492b3..82c5717eb8a 100644
--- a/src/mongo/db/repl/apply_ops.cpp
+++ b/src/mongo/db/repl/apply_ops.cpp
@@ -34,6 +34,7 @@
 #include "mongo/db/repl/apply_ops.h"
 
 #include "mongo/bson/util/bson_extract.h"
+#include "mongo/db/background.h"
 #include "mongo/db/catalog/collection.h"
 #include "mongo/db/catalog/database.h"
 #include "mongo/db/catalog/database_holder.h"
@@ -290,6 +291,18 @@ Status _applyPrepareTransaction(OperationContext* opCtx,
         "applyOps with prepared must only include CRUD operations and cannot have precondition.",
         !info.getPreCondition() && info.areOpsCrudOnly());
 
+    // Block application of prepare oplog entry on secondaries when a concurrent background index
+    // build is running.
+    // This will prevent hybrid index builds from corrupting an index on secondary nodes if a
+    // prepared transaction becomes prepared during a build but commits after the index build
+    // commits.
+    for (const auto& opObj : info.getOperations()) {
+        auto ns = opObj.getField("ns").checkAndGetStringData();
+        if (BackgroundOperation::inProgForNs(ns)) {
+            BackgroundOperation::awaitNoBgOpInProgForNs(ns);
+        }
+    }
+
     // Transaction operations are in its own batch, so we can modify their opCtx.
     invariant(entry.getSessionId());
     invariant(entry.getTxnNumber());