SERVER-76835 Avoid blocking on PBWM and admission control tickets on the sharding metadata refresh path

2 files changed, 18 insertions, 5 deletions

diff --git a/src/mongo/db/s/shard_filtering_metadata_refresh.cpp b/src/mongo/db/s/shard_filtering_metadata_refresh.cpp
index 52338889bf1..ba01b41f2e3 100644
--- a/src/mongo/db/s/shard_filtering_metadata_refresh.cpp
+++ b/src/mongo/db/s/shard_filtering_metadata_refresh.cpp
@@ -489,6 +489,13 @@ void onCollectionPlacementVersionMismatch(OperationContext* opCtx,
         boost::optional<SharedSemiFuture<void>> inRecoverOrRefresh;
 
         {
+            // The refresh threads do not perform any data reads themselves, therefore they don't
+            // need to synchronise with secondary oplog application or go through admission control.
+            ShouldNotConflictWithSecondaryBatchApplicationBlock skipParallelBatchWriterMutex(
+                opCtx->lockState());
+            ScopedAdmissionPriorityForLock skipAdmissionControl(
+                opCtx->lockState(), AdmissionContext::Priority::kImmediate);
+
             boost::optional<Lock::DBLock> dbLock;
             boost::optional<Lock::CollectionLock> collLock;
             dbLock.emplace(opCtx, nss.dbName(), MODE_IS);
diff --git a/src/mongo/db/s/shard_server_catalog_cache_loader.cpp b/src/mongo/db/s/shard_server_catalog_cache_loader.cpp
index fd654f84dee..c3f0ad9d603 100644
--- a/src/mongo/db/s/shard_server_catalog_cache_loader.cpp
+++ b/src/mongo/db/s/shard_server_catalog_cache_loader.cpp
@@ -696,11 +696,6 @@ StatusWith<CollectionAndChangedChunks> ShardServerCatalogCacheLoader::_runSecond
 
     // Read the local metadata.
 
-    // Disallow reading on an older snapshot because this relies on being able to read the
-    // side effects of writes during secondary replication after being signalled from the
-    // CollectionPlacementVersionLogOpHandler.
-    BlockSecondaryReadsDuringBatchApplication_DONT_USE secondaryReadsBlockBehindReplication(opCtx);
-
     return _getCompletePersistedMetadataForSecondarySinceVersion(
         opCtx, nss, catalogCacheSinceVersion);
 }
@@ -1336,6 +1331,17 @@ ShardServerCatalogCacheLoader::_getCompletePersistedMetadataForSecondarySinceVer
     // Keep trying to load the metadata until we get a complete view without updates being
     // concurrently applied.
     while (true) {
+        // Disallow reading on an older snapshot because this relies on being able to read the
+        // side effects of writes during secondary replication after being signalled from the
+        // CollectionPlacementVersionLogOpHandler.
+        BlockSecondaryReadsDuringBatchApplication_DONT_USE secondaryReadsBlockBehindReplication(
+            opCtx);
+
+        // Taking the PBWM and blocking on admission control can lead to deadlock with prepared
+        // transactions, so have internal refresh operations skip admission control
+        ScopedAdmissionPriorityForLock skipAdmissionControl(opCtx->lockState(),
+                                                            AdmissionContext::Priority::kImmediate);
+
         const auto beginRefreshState = [&]() {
             while (true) {
                 auto notif = _namespaceNotifications.createNotification(nss);