void writeDocumentValue(Document document, CompletionHandler completionHandler) throws IOException {
            writeDocument(myOut -> {
                try (JsonGenerator myJson = jsonFactory.createGenerator(myOut)) {
                    new JsonWriter(myJson, tensorShortForm(), tensorDirectValues()).write(document);
                }
            }, completionHandler);
        }
Writes documents to an internal queue, which is flushed regularly.
vespaclient-container-plugin/src/main/java/com/yahoo/document/restapi/resource/DocumentV1ApiHandler.java