SERVER-57063 Ensure that config.collections exists upon configsvr startup

2 files changed, 32 insertions, 1 deletions

diff --git a/src/mongo/db/s/config/sharding_catalog_manager.cpp b/src/mongo/db/s/config/sharding_catalog_manager.cpp
index a13ddcdcabc..0272b7c82ce 100644
--- a/src/mongo/db/s/config/sharding_catalog_manager.cpp
+++ b/src/mongo/db/s/config/sharding_catalog_manager.cpp
@@ -370,7 +370,12 @@ Status ShardingCatalogManager::initializeConfigDatabaseIfNeeded(OperationContext
         }
     }
 
-    Status status = _initConfigIndexes(opCtx);
+    Status status = _initConfigCollections(opCtx);
+    if (!status.isOK()) {
+        return status;
+    }
+
+    status = _initConfigIndexes(opCtx);
     if (!status.isOK()) {
         return status;
     }
@@ -516,6 +521,27 @@ Status ShardingCatalogManager::_initConfigIndexes(OperationContext* opCtx) {
     return Status::OK();
 }
 
+/**
+ * Ensure that config.collections exists upon configsvr startup
+ */
+Status ShardingCatalogManager::_initConfigCollections(OperationContext* opCtx) {
+    // Ensure that config.collections exist so that snapshot reads on it don't fail with
+    // SnapshotUnavailable error when it is implicitly created (when sharding a
+    // collection for the first time) but not in yet in the committed snapshot).
+    DBDirectClient client(opCtx);
+
+    BSONObj cmd = BSON("create" << CollectionType::ConfigNS.coll());
+    BSONObj result;
+    const bool ok = client.runCommand(CollectionType::ConfigNS.db().toString(), cmd, result);
+    if (!ok) {  // create returns error NamespaceExists if collection already exists
+        Status status = getStatusFromCommandResult(result);
+        if (status != ErrorCodes::NamespaceExists) {
+            return status.withContext("Could not create config.collections");
+        }
+    }
+    return Status::OK();
+}
+
 Status ShardingCatalogManager::setFeatureCompatibilityVersionOnShards(OperationContext* opCtx,
                                                                       const BSONObj& cmdObj) {
 
diff --git a/src/mongo/db/s/config/sharding_catalog_manager.h b/src/mongo/db/s/config/sharding_catalog_manager.h
index e8a7da2b356..4e7f4f1ef35 100644
--- a/src/mongo/db/s/config/sharding_catalog_manager.h
+++ b/src/mongo/db/s/config/sharding_catalog_manager.h
@@ -467,6 +467,11 @@ private:
     Status _initConfigIndexes(OperationContext* opCtx);
 
     /**
+     * Ensure that config.collections exists upon configsvr startup
+     */
+    Status _initConfigCollections(OperationContext* opCtx);
+
+    /**
      * Used during addShard to determine if there is already an existing shard that matches the
      * shard that is currently being added.  An OK return with boost::none indicates that there
      * is no conflicting shard, and we can proceed trying to add the new shard.  An OK return