SERVER-56763 Move $merge target collection epoch validation outside of

parsing

This allows us to consult and refresh the catalog cache without holding locks

3 files changed, 17 insertions, 10 deletions

diff --git a/src/mongo/db/pipeline/document_source_merge.h b/src/mongo/db/pipeline/document_source_merge.h
index 54e9620793f..a3623fca678 100644
--- a/src/mongo/db/pipeline/document_source_merge.h
+++ b/src/mongo/db/pipeline/document_source_merge.h
@@ -140,6 +140,18 @@ public:
         return _pipeline;
     }
 
+    void initialize() override {
+        // This implies that the stage will soon start to write, so it's safe to verify the target
+        // collection version. This is done here instead of parse time since it requires that locks
+        // are not held.
+        if (!pExpCtx->inMongos && _targetCollectionVersion) {
+            // If mongos has sent us a target shard version, we need to be sure we are prepared to
+            // act as a router which is at least as recent as that mongos.
+            pExpCtx->mongoProcessInterface->checkRoutingInfoEpochOrThrow(
+                pExpCtx, getOutputNs(), *_targetCollectionVersion);
+        }
+    }
+
 private:
     /**
      * Builds a new $merge stage which will merge all documents into 'outputNs'. If
diff --git a/src/mongo/db/pipeline/process_interface/common_mongod_process_interface.cpp b/src/mongo/db/pipeline/process_interface/common_mongod_process_interface.cpp
index 9ca6c92a5c5..c684ea98e33 100644
--- a/src/mongo/db/pipeline/process_interface/common_mongod_process_interface.cpp
+++ b/src/mongo/db/pipeline/process_interface/common_mongod_process_interface.cpp
@@ -546,12 +546,9 @@ CommonMongodProcessInterface::ensureFieldsUniqueOrResolveDocumentKey(
     boost::optional<std::set<FieldPath>> fieldPaths,
     boost::optional<ChunkVersion> targetCollectionVersion,
     const NamespaceString& outputNs) const {
-    if (targetCollectionVersion) {
-        uassert(51123, "Unexpected target chunk version specified", expCtx->fromMongos);
-        // If mongos has sent us a target shard version, we need to be sure we are prepared to
-        // act as a router which is at least as recent as that mongos.
-        checkRoutingInfoEpochOrThrow(expCtx, outputNs, *targetCollectionVersion);
-    }
+    uassert(51123,
+            "Unexpected target chunk version specified",
+            !targetCollectionVersion || expCtx->fromMongos);
 
     if (!fieldPaths) {
         uassert(51124, "Expected fields to be provided from mongos", !expCtx->fromMongos);
diff --git a/src/mongo/db/pipeline/process_interface/shardsvr_process_interface.cpp b/src/mongo/db/pipeline/process_interface/shardsvr_process_interface.cpp
index 8eccb087f88..1fc0dc6b80d 100644
--- a/src/mongo/db/pipeline/process_interface/shardsvr_process_interface.cpp
+++ b/src/mongo/db/pipeline/process_interface/shardsvr_process_interface.cpp
@@ -73,6 +73,7 @@ void ShardServerProcessInterface::checkRoutingInfoEpochOrThrow(
     const boost::intrusive_ptr<ExpressionContext>& expCtx,
     const NamespaceString& nss,
     ChunkVersion targetCollectionVersion) const {
+
     auto const shardId = ShardingState::get(expCtx->opCtx)->shardId();
     auto* catalogCache = Grid::get(expCtx->opCtx)->catalogCache();
 
@@ -81,11 +82,8 @@ void ShardServerProcessInterface::checkRoutingInfoEpochOrThrow(
     catalogCache->invalidateShardOrEntireCollectionEntryForShardedCollection(
         nss, targetCollectionVersion, shardId);
 
-    // This will throw a 'ShardCannotRefreshDueToLocksHeldInfo' exception if the cache entry is
-    // staler than 'targetCollectionVersion' and 'checkRoutingInfoEpochOrThrow' is called under a DB
-    // lock.
     const auto routingInfo =
-        uassertStatusOK(catalogCache->getCollectionRoutingInfo(expCtx->opCtx, nss, true));
+        uassertStatusOK(catalogCache->getCollectionRoutingInfo(expCtx->opCtx, nss));
 
     auto foundVersion = routingInfo.getVersion(shardId);
     uassert(StaleEpochInfo(nss),