// Change streams can only be run against collections;
                // AutoGetCollectionForReadCommand will raise an error if the given namespace is a
                // view. A change stream may be opened on a namespace before the associated
                // collection is created, but only if the database already exists. If the
                // $changeStream was sent from mongoS then the database exists at the cluster level
                // even if not yet present on this shard, so we allow the $changeStream to run.
                AutoGetCollectionForReadCommand origNssCtx(opCtx, origNss);

                // Resolve the collator to either the user-specified collation or the default
                // collation of the collection on which $changeStream was invoked, so that we do not
                // end up resolving the collation on the oplog.
                invariant(!collatorToUse);
                if (!origNssCtx.getDb() && !request.isFromMongos()) {
                    AutoGetOrCreateDb dbLock(opCtx, origNss.db(), MODE_X);
                    invariant(dbLock.getDb());
                }
                Collection* origColl = origNssCtx.getCollection();
                collatorToUse.emplace(resolveCollator(opCtx, request, origColl));